immune system | Description, Function, & Facts | elecciones2013.info
Demystified · Quizzes · Galleries · Lists · On This Day · Biographies The innate immune system provides this kind of nonspecific .. These molecules also are secreted into the mother's milk and, once they have been ingested by an infant, When this IgM attachment occurs, it causes microorganisms to. Innate Defense – first line of defense; Non-specific responses to infection - 2nd line The immune system is closely tied to the lymphatic system, with B and T .. Hemolytic Disease of the Newborn (HDN) is due to maternal antibodies to the surface of microbes and prevent their attachment to the body's cells (thus . lymphoid system quiz 5 study guide by maynard31 includes 13 questions acquired immunity, active immunity, naturally acquired active immunity, acquired passive immunity, induced passive immunity, innate immunity where a mothers antibodies protect her baby against infections during gestation or in early infancy.
These granulocytes ingest and destroy microorganisms, especially bacteria. Less common are the eosinophils, which are particularly effective at damaging the cells that make up the cuticle body wall of larger parasites. Fewer still are the basophils, which release heparin a substance that inhibits blood coagulationhistamineand other substances that play a role in some allergic reactions see immune system disorder: Very similar in structure and function to basophils are the tissue cells called mast cellswhich also contribute to immune responses.
Granulocytes, which have a life span of only a few days, are continuously produced from stem i.Double-Edged Sword: A Protein with the Power to Heal or Hurt
They enter the bloodstream and circulate for a few hours, after which they leave the circulation and die. Granulocytes are mobile and are attracted to foreign materials by chemical signals, some of which are produced by the invading microorganisms themselves, others by damaged tissues, and still others by the interaction between microbes and proteins in the blood plasma. Some microorganisms produce toxins that poison granulocytes and thus escape phagocytosis; other microbes are indigestible and are not killed when ingested.
By themselves, then, granulocytes are of limited effectiveness and require reinforcement by the mechanisms of specific immunity. Macrophages The other main type of scavenger cell is the macrophage, the mature form of the monocyte. Like granulocytes, monocytes are produced by stem cells in the bone marrow and circulate through the blood, though in lesser numbers.
But, unlike granulocytes, monocytes undergo differentiation, becoming macrophages that settle in many tissues, especially the lymphoid tissues e. Macrophages live longer than granulocytes and, although effective as scavengers, basically provide a different function. Compared with granulocytes, macrophages move relatively sluggishly.
They are attracted by different stimuli and usually arrive at sites of invasion later than granulocytes. Macrophages recognize and ingest foreign particles by mechanisms that are basically similar to those of granulocytes, although the digestive process is slower and not as complete.
This aspect is of great importance for the role that macrophages play in stimulating specific immune responses—something in which granulocytes play no part. Scanning electron micrograph of a macrophage purple attacking a cancer cell yellow. NK cells were first recognized inwhen researchers observed cells in the blood and lymphoid tissues that were neither the scavengers described above nor ordinary lymphocytes but which nevertheless were capable of killing cells.
Although similar in outward appearance to lymphocytes, NK cells contain granules that harbour cytotoxic chemicals. NK cells recognize dividing cells by a mechanism that does not depend on specific immunity. They then bind to these dividing cells and insert their granules through the outer membrane and into the cytoplasm. This causes the dividing cells to leak and die.
NK cells are the third most abundant type of lymphocyte in the body B and T lymphocytes being present in the greatest numbers. They develop from hematopoietic stem cells and mature in the bone marrow and the liver. Nonspecific responses to infection The body has a number of nonspecific methods of fighting infection that are called early induced responses.
They include the acute-phase response and the inflammation response, which can eliminate infection or hold it in check until specific, acquired immune responses have time to develop.
Nonspecific immune responses occur more rapidly than acquired immune responses do, but they do not provide lasting immunity to specific pathogens. Created and produced by QA International. These cytokines include members of the family of proteins called interleukinswhich induce fever and the acute-phase response, and tumour necrosis factor -alpha, which initiates the inflammatory response. Acute-phase response When the body is invaded by a pathogen, macrophages release the protein signals interleukin-1 IL-1 and interleukin-6 IL-6 to help fight the infection.
One of their effects is to raise the temperature of the body, causing the fever that often accompanies infection.
The interleukins increase body temperature by acting on the temperature-regulating hypothalamus in the brain and by affecting energy mobilization by fat and muscle cells. Fever is believed to be helpful in eliminating infections because most bacteria grow optimally at temperatures lower than normal body temperature. But fever is only part of the more general innate defense mechanism called the acute-phase response.
In addition to raising body temperature, the interleukins stimulate liver cells to secrete increased amounts of several different proteins into the bloodstream. These proteins, collectively called acute-phase proteins, bind to bacteria and, by doing so, activate complement proteins that destroy the pathogen. The acute-phase proteins act similarly to antibodies but are more democratic—that is, they do not distinguish between pathogens as antibodies do but instead attack a wide range of microorganisms equally.
Another effect the interleukins have is to increase the number of circulating neutrophils and eosinophils, which help fight infection. Inflammatory response Infection often results in tissue damage, which may trigger an inflammatory response. The signs of inflammation include painswelling, redness, and fever, which are induced by chemicals released by macrophages. These substances promote blood flow to the area, increase the permeability of capillariesand induce coagulation.
The increased blood flow is responsible for redness, and the leakiness of the capillaries allows cells and fluids to enter tissues, causing pain and swelling. These effects bring more phagocytic cells to the area to help eliminate the pathogens. The first cells to arrive, usually within an hour, are neutrophils and eosinophils, followed a few hours later by macrophages.
Macrophages not only engulf pathogens but also help the healing process by disposing of cellular debris which accumulates from destroyed tissue cells and neutrophils that self-destruct after ingesting microorganisms. If infection persists, components of specific immunity—antibodies and T cells —arrive at the site to fight the infection. Specific, acquired immunity It has been known for centuries that persons who contract certain diseases and survive generally do not catch those illnesses again.
Greek historian Thucydides recorded that, when the plague was raging in Athens during the 5th century bce, the sick and dying would have received no nursing at all had it not been for the devotion of those who had already recovered from the disease; it was known that no one ever caught the plague a second time. The same applies, with rare exceptions, to many other diseases, such as smallpoxchicken poxmeaslesand mumps.
Yet having had measles does not prevent a child from contracting chicken pox or vice versa. The protection acquired by experiencing one of these infections is specific to that infection; in other words, it is due to specific, acquired immunity, also called adaptive immunity. Acquired immunity depends on the activities of T and B lymphocytes T and B cells. One part of acquired immunity, humoral immunity, involves the production of antibodies by B cells. The other part, cell-mediated immunity, involves the actions of T cells.
When an antigen such as a bacterium enters the body, it is attacked and engulfed by macrophages, which process and display parts of it on their cell surface. A helper T cell, recognizing the antigen displayed, initiates maturation and proliferation of other T cells. Cytotoxic killer T cells develop and attack foreign and infected cells. B cells stimulated by the presence of antigen are activated by helper T cells to divide and form antibody-producing cells plasma cells.
Released antibody binds to antigen, marking the cell for destruction. Helper T cells also induce the development of memory T and B cells needed to mount future immune responses on reinfection with the same pathogen. There are other infectious conditions, such as the common coldinfluenzapneumoniaand diarrheal diseases, that can be caught again and again; these seem to contradict the notion of specific immunity. But the reason such illnesses can recur is that many different infectious agents produce similar symptoms and thus the same disease.
For example, more than viruses can cause the cluster of symptoms known as the common cold. Consequently, even though infection with a particular agent does protect against reinfection by that same pathogen, it does not confer protection from other pathogens that have not been encountered. Acquired immunity is dependent on the specialized white blood cells known as lymphocytes.
This section describes the various ways in which lymphocytes operate to confer specific immunity. Although pioneer studies were begun in the late 19th century, most of the knowledge of specific immunity has been gained since the s, and new insights are continually being obtained. Lymphocytes are mainly a dormant population, awaiting the appropriate signals to be stirred to action.
The inactive lymphocytes are small, round cells filled largely by a nucleus. Although they have only a small amount of cytoplasm compared with other cells, each lymphocyte has sufficient cytoplasmic organelles small functional units such as mitochondriathe endoplasmic reticulumand a Golgi apparatus to keep the cell alive.
Lymphocytes move only sluggishly on their own, but they can travel swiftly around the body when carried along in the blood or lymph. The majority are concentrated in various tissues scattered throughout the body, particularly the bone marrowspleenthymuslymph nodestonsilsand lining of the intestines, which make up the lymphatic system. Organs or tissues containing such concentrations of lymphocytes are described as lymphoid. The lymphocytes in lymphoid structures are free to move, although they are not lying loose; rather, they are confined within a delicate network of lymph capillaries located in connective tissues that channel the lymphocytes so that they come into contact with other cells, especially macrophages, that line the meshes of the network.
This ensures that the lymphocytes interact with each other and with foreign materials trapped by the macrophages in an ordered manner. The human lymphatic system, showing the lymphatic vessels and lymphoid organs. T and B cells Lymphocytes originate from stem cells in the bone marrow ; these stem cells divide continuously, releasing immature lymphocytes into the bloodstream. Some of these cells travel to the thymuswhere they multiply and differentiate into T lymphocytes, or T cells.
The T stands for thymus-derived, referring to the fact that these cells mature in the thymus. Once they have left the thymus, T cells enter the bloodstream and circulate to and within the rest of the lymphoid organs, where they can multiply further in response to appropriate stimulation.
About half of all lymphocytes are T cells. NIAID Some lymphocytes remain in the bone marrow, where they differentiate and then pass directly to the lymphoid organs. They are termed B lymphocytes, or B cellsand they, like T cells, can mature and multiply further in the lymphoid organs when suitably stimulated. Although it is appropriate to refer to them as B cells in humans and other mammals, because they are bone-marrow derived, the B actually stands for the bursa of Fabriciusa lymphoid organ found only in birds, the organisms in which B cells were first discovered.
B and T cells both recognize and help eliminate foreign molecules antigenssuch as those that are part of invading organisms, but they do so in different ways.
B cells secrete antibodiesproteins that bind to antigens. Since antibodies circulate through the humours i. T cells, in contrast, do not produce antibodies but instead directly attack invaders. Because this second type of acquired immunity depends on the direct involvement of cells rather than antibodies, it is called cell-mediated immunity.
These two types of specific, acquired immunity, however, are not as distinct as might be inferred from this description, since T cells also play a major role in regulating the function of B cells. In many cases an immune response involves both humoral and cell-mediated assaults on the foreign substance.
Furthermore, both classes of lymphocytes can activate or enhance a variety of nonspecific immune responses. Ability to recognize foreign molecules Receptor molecules Lymphocytes are distinguished from other cells by their capacity to recognize foreign molecules. Recognition is accomplished by means of receptor molecules. A receptor molecule is a special protein whose shape is complementary to a portion of a foreign molecule.
This complementarity of shape allows the receptor and the foreign molecule to conform to each other in a fashion roughly analogous to the way a key fits into a lock. Receptor molecules are either attached to the surface of the lymphocyte or secreted into fluids of the body.
B and T lymphocytes both have receptor molecules on their cell surfaces, but only B cells manufacture and secrete large numbers of unattached receptor molecules, called antibodies. Antibodies correspond in structure to the receptor molecules on the surface of the B cell. Antigens Any foreign material—usually of a complex nature and often a protein—that binds specifically to a receptor molecule made by lymphocytes is called an antigen.
Antigens include molecules found on invading microorganisms, such as virusesbacteriaprotozoansand fungias well as molecules located on the surface of foreign substances, such as pollendust, or transplanted tissue. When an antigen binds to a receptor molecule, it may or may not evoke an immune response. Antigens that induce such a response are called immunogens. Thus, it can be said that all immunogens are antigens, but not all antigens are immunogens.
For example, a simple chemical group that can combine with a lymphocyte receptor i. Although haptens cannot evoke an immune response by themselves, they can become immunogenic when joined to a larger, more complex molecule such as a protein, a feature that is useful in the study of immune responses.
Many antigens have a variety of distinct three-dimensional patterns on different areas of their surfaces. Each pattern is called an antigenic determinant, or epitopeand each epitope is capable of reacting with a different lymphocyte receptor.
Some antigenic determinants are better than others at effecting an immune response, presumably because a greater number of responsive lymphocytes are present. It is possible for two or more different substances to have an epitope in common. In these cases, immune components induced by one antigen are able to react with all other antigens carrying the same epitope.
Such antigens are known as cross-reacting antigens. T cells and B cells differ in the form of the antigen they recognize, and this affects which antigens they can detect. B cells bind to antigen on invaders that are found in circulation outside the cells of the body, while T cells detect only invaders that have somehow entered the cells of the body.
Thus foreign materials that have been ingested by cells of the body or microorganisms such as viruses that penetrate cells and multiply within them are out of reach of antibodies but can be eliminated by T cells. Diversity of lymphocytes The specific immune system in other words, the sum total of all the lymphocytes can recognize virtually any complex molecule that nature or science has devised.
This remarkable ability results from the trillions of different antigen receptors that are produced by the B and T lymphocytes. Each lymphocyte produces its own specific receptor, which is structurally organized so that it responds to a different antigen. After a cell encounters an antigen that it recognizes, it is stimulated to multiply, and the population of lymphocytes bearing that particular receptor increases.
How is it that the body has such an incredible diversity of receptors that are always ready to respond to invading molecules? To understand this, a quick review of genes and proteins will be helpful. Antigen receptor molecules are proteinswhich are composed of a few polypeptide chains i. The sequence in which the amino acids are assembled to form a particular polypeptide chain is specified by a discrete region of DNAcalled a gene.
But if every polypeptide region of every antigen receptor were encoded by a different gene, the human genome all the genetic information encoded in the DNA that is carried on the chromosomes of cells would need to devote trillions of genes to code just for these immune system proteins.
Since the entire human genome contains approximately 25, genes, individuals cannot inherit a gene for each particular antigen receptor component. Instead, a mechanism exists that generates an enormous variety of receptors from a limited number of genes. What is inherited is a pool of gene segments for each type of polypeptide chain. As each lymphocyte matures, these gene segments are pieced together to form one gene for each polypeptide that makes up a specific antigen receptor.
This rearrangement of alternative gene segments occurs predominantly, though not entirely, at random, so that an enormous number of combinations can result. Additional diversity is generated from the imprecise recombination of gene segments—a process called junctional diversification—through which the ends of the gene segments can be shortened or lengthened. The genetic rearrangement takes place at the stage when the lymphocytes generated from stem cells first become functional, so that each mature lymphocyte is able to make only one type of receptor.
Thus, from a pool of only hundreds of genes, an unlimited variety of diverse antigen receptors can be created. Still other mechanisms contribute to receptor diversity. Superimposed on the mechanism outlined in simplified terms above is another process, called somatic mutation.
Mutation is the spontaneous occurrence of small changes in the DNA during the process of cell division. Although somatic mutation can be a chance event in any body cell, it occurs regularly in the DNA that codes for antigen receptors in lymphocytes.
Thus, when a lymphocyte is stimulated by an antigen to divide, new variants of its antigen receptor can be present on its descendant cells, and some of these variants may provide an even better fit for the antigen that was responsible for the original stimulation.
B-cell antigen receptors and antibodies The antigen receptors on B lymphocytes are identical to the binding sites of antibodies that these lymphocytes manufacture once stimulated, except that the receptor molecules have an extra tail that penetrates the cell membrane and anchors them to the cell surface.
Thus, a description of the structure and properties of antibodies, which are well studied, will suffice for both. Basic structure of the immunoglobulin molecule Antibodies belong to the class of proteins called globulins, so named for their globular structure.
Collectively, antibodies are known as immunoglobulins abbreviated Ig. All immunoglobulins have the same basic molecular structure, consisting of four polypeptide chains. Two of the chains, which are identical in any given immunoglobulin molecule, are heavy H chains; the other two are identical light L chains. The terms heavy and light simply mean larger and smaller.
Each chain is manufactured separately and is encoded by different genes. The four chains are joined in the final immunoglobulin molecule to form a flexible Y shape, which is the simplest form an antibody can take. The four-chain structure of an antibody, or immunoglobulin, moleculeThe basic unit is composed of two identical light L chains and two identical heavy H chains, which are held together by disulfide bonds to form a flexible Y shape.
Each chain is composed of a variable V region and a constant C region. At the tip of each arm of the Y-shaped molecule is an area called the antigen-bindingor antibody-combining, site, which is formed by a portion of the heavy and light chains.
Every immunoglobulin molecule has at least two of these sites, which are identical to one another. The antigen-binding site is what allows the antibody to recognize a specific part of the antigen the epitopeor antigenic determinant. Chemical bonds called weak bonds then form to hold the antigen within the binding site. The heavy and light chains that make up each arm of the antibody are composed of two regions, called constant C and variable V.
These regions are distinguished on the basis of amino acid similarity—that is, constant regions have essentially the same amino acid sequence in all antibody molecules of the same class IgG, IgM, IgA, IgD, or IgEbut the amino acid sequences of the variable regions differ quite a lot from antibody to antibody. This makes sense, because the variable regions determine the unique shape of the antibody-binding site. The tail of the molecule, which does not bind to antigens, is composed entirely of the constant regions of heavy chains.
The variable and constant regions of both the light and the heavy chains are structurally folded into functional units called domains. Each light chain consists of one variable domain VL and one constant domain CL.
The tail of the antibody determines the fate of the antigen once it becomes bound to the antibody. Variable V and constant C domains within the light L and heavy H chains of an antibody, or immunoglobulin, molecule. It provides the molecule with flexibility, which is very useful in binding antigens. This flexibility can actually improve the efficiency with which an antigen binds to the antibody.
It can also help in cross-linking antigens into a large lattice of antigen-antibody complexes, which are easily identified and destroyed by macrophages. A The hinge region of an antibody molecule opens and closes to allow better binding between the antibody and antigenic determinants on the surface of an antigen. B Hinge flexibility also facilitates the cross-linking of antigens into large antigen-antibody complexes. Classes of immunoglobulins The term constant region is a bit misleading in that these segments are not identical in all immunoglobulins.
Rather, they are basically similar among broad groups. All immunoglobulins that have the same basic kinds of constant domains in their H chains are said to belong to the same class. Each class has its own properties and functions determined by the structural variations of the H chains. In addition, there are two basic kinds of L chains, called lambda and kappa chains, either of which can be associated with any of the H chain classes, thereby increasing still further the enormous diversity of immunoglobulins.
The five main classes of antibodies immunoglobulins: When an injury occurs, a capillary and several tissue cells are apt to rupture, releasing histamine and kinins. These cause the capillaries to dilate, become more permeable, and leak fluid into these tissues. Dilation and fluid leaking into the tissues causes swelling, redness, and heat. The swelling and kinins stimulate nerve endings, causing pain.
If there has been a break in the skin due to the injury, invading microbes may enter. A common cause of inflammation after surgery is serous fluid. This is a mixture of plasma, lymph and interstitial fluids seeping from the damaged cells and vessels. If enough serous fluid accumulates a mass called a seroma may form. Treatment of a seroma may involve the removal of the fluid with a needle into a syringe, a process called aspiration.
Phagocytosis by neutrophils and macrophages In the event of a break in the skin, neutrophils, monocytes and macrophages arrive and attempt to engulf and destroy the invaders. Phagocytosis is receptor-mediated event, which ensures that only unwanted particles are ingested. Stimulated macrophages can bring about an explosive increase in the number of leukocytes by producing Colony Stimulating Factors CSFs.
The CSFs pass by way of the blood to the bone marrow, where they stimulate the production and the release of white blood cells WBCsprimarily neutrophils. Lymphocytes in nearby lymph nodes produce specific antibodies to attack the microbes. During the conflict, some neutrophils die and become mixed with dead tissue, bacteria, living white cells, etc.
This thick yellow-white fluid is called pus. When a person has an illness, an examination of the numbers and types of WBC's in their blood can be very useful. Complement System[ edit ] Complement protein attacking a cell membrane. The complement system is a biochemical cascade of the immune system that helps clear pathogens from an organism, and promote healing. It is derived from many small plasma proteins that work together to form the primary end result of cytolysis by disrupting the target cell's plasma membrane.
Complement is activated by antigen-antibody complexes and causes holes to form in the plasma membrane of foreign microbes or cells lysis. The complement system is considered a nonspecific defense, but it can be activated against specific microbes that have been marked with antibodies. Hemolytic transfusion reactions are caused by complement activation after a person expresses antibodies against the antigens found on the inappropriately donated blood.
Hemolytic Disease of the Newborn HDN is due to maternal antibodies against the Rh factor crossing the placenta, binding to the baby's red blood cells, and stimulating the baby's own complement system to lyse its red blood cells.
Interferon in response to viral infection[ edit ] Interferon IFNs are naturally occurring glycoproteins involved in non-specific immune responses. Interferons do just as their name states they "interfere" with viral growth. Interferons are initiated from a cell that has been infected by a virus. When a cell has been infected by a virus the virus will then cause the cell to make viral nucleic acid.
This nucleic acid acts as a signal and it causes the cell to realize that it has been infected with a virus. So the cell will start making and sending out interferons. The IFN's that the cell sends out go to nearby healthy cells and warns them of a virus. The healthy cells then start intracellular changes that help the cells to be more resistant to the virus. Adaptive Defense Specific Defense--third line of defense [ edit ] This part of the immune system directly targets invading microbes.
Our specific immune defenses respond to antigens. An antigen is a protein or polysaccharide molecule, typically on the cell membrane, that the body recognizes as nonself. They are found on microbes, foreign cells, or on cancer cells.
Normally our immune system does not respond to our own antigens if it does, then this is an autoimmune disease. Sometimes we develop an immune response to a harmless antigen, such as pollen or cat dander this is an allergic response. Lymphocytes[ edit ] Specific immunity is dependent upon two types of lymphocytes, the B cells and the T cells.
Their names are based on where in the body they mature. B cells mature in the bone marrow, and T cells mature in the thymus gland. In comparison, both B and T cells can recognize and target antigen-bearing cells, although they go about this in different ways. B and T cell lymphocytes are capable of recognizing an antigen because they have specific receptor molecules on their surface which exactly fit individual antigens like a lock and a key.
Any B or T cell can only respond to one type of antigen. The body does not know ahead of time which antigens it will encounter, but rather makes receptor sites for a huge number of possible antigens.
It is estimated that for the million or so antigens we encounter in our lifetime we have an equal number of specific lymphocytes for each possible antigen. B Cells Produce Antibodies[ edit ] B cell lymphocytes are responsible for antibody-mediated immunity humoral immunity.
They produce antibodies, which are proteins that bind with and neutralize specific antigens. Antibodies do not directly kill bacteria, but mark them for destruction. When antibodies bind to viruses they can prevent the viruses from infecting cells. When antibodies bind to toxins they can neutralize the toxin why we get immunized against the tetanus toxin.
Humoral immunity works best fighting against target viruses, bacteria, and foreign molecules that are soluble in blood and lymph before the bacteria or viruses have entered into cells extracellular bacteria and extracellular viruses.
B cells produce two different types of cells: Then they travel in the bloodstream, distributing throughout the lymph nodes, spleen, and tonsils. Once B cells reach their destination, they remain inactive until they encounter a foreign cell with an antigen that matches their particular receptor site most B cells remain inactive for your entire life.
The foreign antigen can be presented to the B cell directly, but usually macrophages and T cell lymphocytes helper T cells interact with B cells as Antigen Presenting Cells to bring about antibody production. Upon such an encounter, the B cell's receptors will bind to the antigen.
The appropriate B cell is turned on or stimulated. It then grows bigger, and rapidly multiplies into a large homogenous group clone. Most of these cells are plasma cells, which actively secrete antibody that will bind with the original stimulating antigen. While most of the B cells remain in the lymphatic system, the antibodies are secreted into the lymph fluid which then enters into the blood plasma to circulate throughout the body.
Although the clone cells only live a few days, their antibodies remain and circulate in the blood and lymph, gradually decreasing in number. They can attach to the surface of a microbe and make it more easily phagocytized by neutrophils, monocytes and macrophages.
Anything that simplifies phagocytosis is called an opsonin. The process of antibodies attaching to invaders can be termed 'opsonization. Still other antibodies can bind to the surface of microbes and prevent their attachment to the body's cells thus preventing viruses from entering host cells. Also, some of them can stimulate nine proteins found in plasma, called complement.
Memory B cells At the time of activation some of the clones become memory B cells.
These cells are long lived and have recorded the information about the foreign antigen so antibodies can be made more quickly, and in greater amount, in case a second exposure should occur.
Since the second response is much stronger than the first and puts more antibodies into circulation, we often receive "booster shots" for immunizations. Macrophages phagocytize invading microbes and present parts of the microbe antigens to the T cell lymphocytes. The appropriate T cell is turned on or stimulated. The activated T cell rapidly multiplies into a large homogenous group clone of cytotoxic T cells Tc cells.
These cells record the information about the foreign antigen so T cells can respond more quickly, and more strongly, if a second exposure occurs. TH cell stimulate other T cells and B cells by releasing cytokines and other stimulatory chemicals. Ts cells suppress the immune response. Experience has shown that cell mediated immunity is most useful to the body by: Protecting against microbes which exist inside of our body's cells intracellular bacteria and intracellular viruses.
Protecting against fungal infections. Protecting against protozoan parasites. Protecting against cancer cells. Immune Response Pathways[ edit ] The innate response starts first, and it is reinforced by the more specific acquired response. The two pathways are interconnected, so cooperation and communication is essential. Inflammation[ edit ] What happens when bacteria invade? If the first line of defense fails, bacteria can reach the extracellular fluid.
There they usually cause an inflammatory response. This response coats antigens on the bacterial surface, with antibodies. Then in return the antibodies will ingest the antigens with phagocytic cells.
This is characterized by a red, swollen warm area that is tender or painful. In addition to the nonspecific inflammatory response, lymphocytes attracted to the area produce antibodies keyed to the specific type of bacteria. If the infection continues it will produce a fever.
What causes a fever? During an infection macrophages may release cytokines see glossarysuch as interleukin-1, that travel to the hypothalamus and induce a change in the thermostat setting. When the thermostat is raised to a new normal temperature, the previous body temperature now registers as too cold. To increase the temperature to the new level, our body shunts blood away from the skin leaving it feeling cold and clammythe heart rate increases, and we shiver to generate heat until we reach the new set point.
The hypothalamus may subsequently lower the thermostat, in which case we suddenly feel hot and start to sweat as our body attempts to cool off.
Evolution of the immune system in humans from infancy to old age
A person may cycle between chills and sweats during the course of an infection. While a fever can be dangerous if it gets too high, or if a patient is weak or has heart trouble, there is some evidence suggesting that the body may overcome an infection faster if a fever is allowed to run its course. Intracellular Defense[ edit ] What happens when virus's invade the body?
First they encounter an extracellular phase just like the bacteria did. In the early stages of a viral infection, innate immune responses and antibodies can help control the invasion of the virus. Once the virus enters the body's host cells cytotoxic T lymphocytes are the main defense against intracellular viruses. These cells look for infected host cells, then destroy them. Antigen-specific Responses[ edit ] Acquired immunity responses are antigen-specific responses in which the body recognizes a foreign substance and selectively reacts to it.
This is mediated primarily by lymphocytes. Acquired immunity overlaps with the process of innate immunity. Acquired immunity can be subdivided into active immunity and passive immunity.
Active Immunity occurs when the body is exposed to a pathogen and produces its own antibodies. Active immunity is active because it is the "activation" of your immune system. Active immunity can occur naturally, when a pathogen invades the body, or artificially, like when we are given vaccinations containing disabled or killed pathogens. The body does require prior exposure to an antigen to develop an active immunity. Some parents expose their children to some antigens so they will have immunity to these diseases later in life.
Passive Immunity occurs when we acquire antibodies made by another human or animal. Passive immunity is passive because it requires no response from the person's immune system. In passive immunity you are not presenting the body with foreign antigens. Therefore your immune system will not need to use B cells, and we know that if the B cells are never introduced your body isn't making antibodies and it isn't making memory B cells.
The transfer of antibodies from mother to fetus across the placenta is one example. Injections containing antibodies are another. Sometimes travelers going abroad may be injected with gamma globulin, but this passive immunity last only about three months. Passive immunizations are used to protect people who have been exposed to infections or toxins, like snake venom or tetanus. Left alone, the antigen is not harmful to the body, but if someone is sensitive to the antigen, the body produces an inflammatory response designed to get rid of it.
Allergic inflammatory responses can range from mild tissue damage to fatal reactions. The immune response in allergies is called sensitivity or hypersensitivity to the antigen. Immediate hypersensitivity reactions are mediated immune destruction by antibodies and occur within minutes of exposure to antigens, which are called allergens. Delayed hypersensitivity reactions are mediated by helper T cells and macrophages and may take several days to develop. What happens during a immediate hypersensitivity reaction?
Upon reexposure, the body reacts more strongly and rapidly. The allergen binds to IgE already present on mast cells, triggering the immediate release of histamine, cytokines, and other mediators that cause allergic symptoms.
The severity of the reaction varies, ranging from localized reactions near the site of where the allergen entered, such as a rash. To the most severe allergic reaction called anaphylaxis. In an anaphylactic reaction, massive release of histamine and other cytokines cause widespread vasodilation, circulatory collapse, and severe bronchoconstriction.
Unless treated promptly, anaphylaxis can result in death. Skin tests for allergies of certain allergens can be injected into the skin. This is a good way to find out what one might be allergic to so they can eliminate further exposure.
Allergens that can cause immediate hypersensitivity include bee stings, pollen and certain foods. Allergies that cause chronic allergic rhinitis and asthma are highly due to dust mites dermatophgoides. It is not their bodies that cause the reaction, but rather it's feces. Allergic attacks usually stop when the histamine has been depleted. This can be stopped faster with an antihistamine drug or nasal spray.
What happens in a delayed hypersensitivity? It could take hours or days for symptoms to occur in a delayed hypersensitivity. Delayed hypersensitivity is cell mediated with a T lymphocyte response. Secretion of lymphokines, instead of histamine, happens in a delayed hypersensitivity. So, the treatment would be a corticosteroid instead of an antihistamine. Examples of a delayed hypersensitivity would be, poison sumac, poison oak and poison ivy.
Skin tests for certain diseases are also considered examples like TB test and the Mantoux test. Infectious Organisms and Immunization[ edit ] Beneficial Organisms Intestinal bacteria Bacteria are prokaryotic before nucleus cells that we see usually as bacilli rods or cocci spheres.
While they are the major cause of many diseases both fatal and mild, bacteria are also our friends and can be of great service to us. Many bacteria in our bodies help prevent pathogens from becoming established.
The large intestine is packed with normal microflora that digest substances otherwise indigestible. This process provides our bodies with additional vitamins, fatty acids and nutrients. Another example is the microflora that is in the vagina that helps maintain an acidic pH, which discourages the growth of infectious organisms. These are examples of our immune system's first line of defense.
Harmful Organisms Viruses Viruses are non-living particles consisting of protein and nucleic acid that infect cells in biological organisms. They can reproduce only by invading and taking over other cells as they lack the cellular machinery for self reproduction. A virus is about ten times smaller than a bacteria. Some viruses you will recognize are: Some viruses are particularly dangerous because they can undergo a period of latency, during which they are hidden in the cell and do not reproduce.
Influenza and HIV are examples of viruses that frequently mutate, thus making it nearly impossible to achieve a long-lasting immunity. Bacteria Bacteria can be deadly. They are the major cause of preventable infections and death. Some well known illnesses are caused by bacteria: Because bacterial cells are different from human cells, compounds can be found that can kill specific bacterial targets while leaving the human patient unharmed.
Antibacterial agents can be successful in wiping out a bacterial infection. The problem with antibiotics is that many strains of bacteria are growing resistant to them.
Plus, our bodies are not getting the chance to develop immunity to certain bacteria. It may be better to use probiotics new supplements that promote the growth of healthy and helpful bacteria rather than depend on antibiotics so much. Protozoans The protozoans are mostly eukaryotic unicellular organisms with organelles and a nucleus. Two to four million people die each year from malaria, a million of these are under the age of five.
Fungi Fungi are more like animals and humans than they are like bacteria because of their eukaryotic cells. Though they produce large, visible colonies on old bread, molds and yeasts are in the category of microscopic fungi. Yeasts are one-celled and reproduce by budding. Molds exist as cell chains, called hyphae.
Mycoses are diseases caused by fungi. Because of the similarity between human cells and fungal cells, it has been difficult for scientists to design antibiotics that are effective against fungi and do not harm humans. Some of the diseases caused by fungi are: Diagnosis Infectious diseases are diagnosed by laboratory techniques such as microscopy and culture. Since many bacteria have no color, scientists have developed special staining procedures to more accurately diagnose.
Culture Bacteria and fungi can be identified by growing them on plates until colonies are visible. Viruses are cultured on eggs or live cells. Antibiotic sensitivity After colonies of bacteria are grown on plates, discs are placed on the plates that contain different antibiotics. Bacteria will not grow around the most effective antibiotic. Tests for viruses Since viruses are too small to be seen with a light microscope, viral infections can be diagnosed indirectly by their effects on cells.
Some viruses cause changes to the surface of cultured cells, causing them to stick together. Immunization While some infectious diseases are common and can occur many times in the same person, others can only occur once in a lifetime thanks to the immune system and it's ability to remember the organism and prevent following infections. To avoid an epidemic of a grave disease such as polio, before the disease can be acquired, an immunization can create a man-made "memory". Active immunization A person receives an injection vaccine that contains dead or harmless living forms of an organism.
The vaccine stimulates the immune system to produce antibodies and memorize the organism. If there is a later exposure to this organism and subsequent infection, the antibodies will stop the infection. Passive immunization Blood containing antibodies is taken from animals or humans who have recently had an infection.
Blood serum is made that contains the antibodies, and then injected into the person. The antibodies either attack an infection that is present or provide short-term protection.
Genetically engineered viruses Genetic engineering is a technique that alters or changes the DNA of a plant or animal by inserting new genetic information from another organism. After these organisms replicate, vaccines and hormones are made that can help fight disease.
The bacteria produces viral antigens which are then implanted to stimulate the immune system. Immune System Disorders[ edit ] The immune system is a very complex and highly developed system, yet it has a very simple mission, seek and destroy invaders. When the immune system does not function properly it leaves the body open for attacks from an array of diseases. We classify these into three broad categories; autoimmunity, immunodeficiencies, and hypersensitivities.
Anything that can trigger the immune response is called an antigen. An antigen can be a microbe such as a virus, or even a part of a microbe. Tissues of cells from another person also carry nonself markers and act as antigens. This explains why tissue transplants can be rejected. In abnormal situations, the immune system can mistake self for nonself and launch an attack against the body's own cells or tissues. The result is called an autoimmune disease. Some forms of arthritis and diabetes are autoimmune diseases.
In other cases, the immune system responds to a seemingly harmless foreign substance such as a dust mite. The result is allergy, and this kind of antigen is called an allergen. The Allergic response[ edit ] Type 1 hypersensitivity is an allergic reaction provoked by reexposure to a specific antigen. Exposure may be by ingestion, inhalation, injection, or direct contact. The reaction is mediated by IgE antibodies and produced by the immediate release of histamine, tryptase, arachidonate and derivatives by basophils and mast cells.
This causes an inflammatory response leading to an immediate within seconds to minutes reaction. The reaction may be either local or systemic. Symptoms vary from mild irritation to sudden death from anaphylactic shock. Treatment usually involves epinephrine, antihistamines, and corticosteroids. Hay Fever Hay fever involves an allergic reaction to pollen and results in allergic rhinitis inflammation of the nasal mucosa. It is most common in the haying season, which is why the ailment was named hay fever.
A virtually identical reaction occurs with allergy to mold, animal dander, dust, and similar inhaled allergens. Particulate matter in polluted air and chemicals such as chlorine and detergents, which can normally be tolerated, can greatly aggravate the condition. The pollens that cause hay fever vary from person to person and from region to region; generally speaking, the tiny, hardly visible pollens of wind-pollinated plants are the predominant culprits.
Autoimmune Disorders[ edit ] For reasons we do not fully understand, sometimes the immune system attacks the body the way it normally would attack a germ or foreign substance. The genes some people inherit can contribute to their susceptibility to develop an autoimmune disease. Most autoimmune diseases affect woman more than men. In Juvenile-onset diabetes the immune system starts attacking and eliminating the cells in the pancreas that make insulin.
Multiple Sclerosis is a chronic degenerative disorder of the central nervous system where the immune system starts attacking and destroying vital myelin in the brain and spinal cord. This causes multiple sclerosis scars on the myelin sheath resulting in loss of nerve function. Another fairly known disorder is Rheumatoid Arthritis this is when the immune system starts attacking the tissue inside your joints.