patho immune and abnormal responses

antigens (or immunogens) are either foreign substances or human cell surface antigens that are unique (except in identical pairs) in each individual. They are usually composed of complex proteins or polysaccharides, or a combo of molecules such as glycoproteins. Antigens activate the immune system to produce specific antibodies. The antigens representing self are present on an individual's plasma membranes. These antigen molecules are coded by a group of genes inherited from the parents, called major histocompatability complex (MHC) located on chromosome 6. Owing to the large number of possible combos of genes that may be inherited from the parents, it is unlikely that two individuals would ever have the same antigens, with the exception of identical twins. Major histocompatability complex molecules are useful in detecting changes in cell membranes altered by viruses or cancerous changes and alerting the immune system of their presence. Human MHC is also known as human leukocyte antigen (HLA), because it was first detected on the cell membranes of leukocyes. These antigens are also used to provide the close match for a tissue transplant; the immune system will be activated by the presence of cells with different MHC molecules. The immune system generally tolerates self-antigens on its cells, thus no immune response is initiated against its own cells. Autoimmune diseases are an exception in which the immune system no longer recognizes self from non-self and begins to attack its own cells/structures or organs

Antigens

source of stem cells, leukocytes, and maturation of B lymphocytes

Bone marrow

two subgroups of t cells have gained prominence as markers in patients with acquired immunodeficiency syndrome (AIDS). t helper cells have CD4 molecules as receptors on the cell membrane, and the killer t cells have CD8 molecules. These receptors are important in t cell activation. Although the CD8+ killer cells are primarily cytotoxic, CD4+t cells regulate all the cells in the immune system, the b and t lymphocytes, macrophages, and NK cells, by secreting the messenger cytokines. The human immunodeficiency virus (HIV) destroys the CD4 cells, thus crippling the entire immune system. The ratio of CD4 to CD8 t cells (2:1) is closely monitored in people infected with HIV as a reflection of the progress of the infection.

CD4 and CD8

The macrophage is critical in the initiation of the immune response. Macrophages develop from monocytes, part of the mononuclear phagocytic system that was formerly known as the reticuloendothelial system. Macrophages occur throughout the body in such tissues as the liver, lungs, and lymph nodes. They are large phagocytic cells that intercept and engulf foreign material and then process and display the antigens from the foreign material on their cell membranes; the lymphocytes respond to this display, thus initiating the immune response. Macrophages also secrete chemicals such as monokins and interleukins that play a role in the activation of additional lymphocytes and in the inflammatory response, which accompanies a secondary immune response.

Cells

the immune system consists of lymphoid structures, immune cells, tissues concerned with immune cell development, and chemical mediators. The lymphoid structures, including the lymph nodes, the spleen and tonsils, the intestinal lymphoid tissue, and the lymphatic circulation, form the basic structure within which the immune response can function. The immune cells, or lymphocytes, as well as macrophages provide the specific mechanism for the identification and removal of foreign material. All immune cells originate in the bone marrow, and the bone marrow and thymus have roles in the maturation of the cells. The thymus is significant during fetal development in that it programs the immune system to ignore self-antigens. When this process is faulty, the body may attack its own tissues as non-self. The blood and circulatory system provide a major transportation and communication network for the immune system.

Components of the immune system

one type of rejection occurs when the host, or recipient's, immune system rejects the graft (host-versus-graft disease [HVGD], a possibility with kidney transplants. The other type of rejection that occurs is when the graft tissue contains t cells that attack the host cells (graft-versus-host disease [GVHD]0, as may occur in bone marow transplants.

HVGD and GVHD

found in secretions such as tears and saliva, in mucous membranes, and in colostrum to provide protection for newborn child

IgA- monomer, dimer

attached to b cells; activates b cells

IgD- monomer

binds to mast cells in skin and mucous membranes; when linked to allergen, causes release of histamine and other chemicals, resulting in inflammation

IgE- monomer

most common antibody in the blood; produced in both primary and secondary responses; activates complement, includes antibacterial, antiviral, and antitoxin antibodies. Crosses placenta, creates passive immunity in newborn

IgG-monomer

bound to b cells in circulation and is usually the first to increase in the immune response; activates complement; forms natural antibodies; is involved in blood ABO type incompatibility reaction

IgM-pentamer

contain many lymphocytes. Filter body fluids, remove foreign matter, immune response

Lymphatic tissue and organs

-hyperacute rejection occurs immediately after transplantation as circulation to the site is re-established. This is a greater risk in patients who have pre-existing antibodies, perhaps from prior blood transfusions. The blood vessels are affected, resulting in lack of blood flow to the transplanted tissue. -Acute rejection develops after several weeks when unmatched antigens cause a reaction. -chronic or late rejection occurs after months or yrs, w/gradual degeneration of the blood vessels.

Rejection may occur at any time:

the immune system is responsible for the body's defenses. The system has a nonspecific response and a specific response mechanism. In specific defense the immune system is responding to particular substances, cells, toxins, or proteins, which are perceived as foreign to the body and therefore unwanted or potentially dangerous. The specific immune response is intended to recognize and remove undesirable material from cells, tissues, and organs.

Review of the Immune System

gland located in the mediastinum, large in children, decreasing size in adults. Site of maturation and proliferation of T lymphocytes

Thymus

1. first exposure to allergen--> immune system--> 2. IgE forms on mast cells and basophils in tissues. 3. Sensitized mast cells and basophils for second exposure. 4. Release of mediators (histamine). 5. Inflammation- vasodilation and increased permeability of blood vessels causes edema, redness and pruritis (itching)

Type I hypersensitivity, allergic reaction

allergies are very common and appear to be increasing in incidence and severity; particularly in young children. Allergic reactions take many forms, including skin rashes, hay fever, vomiting, and anaphylaxis. A tendency toward allergic conditions in inherited, and the manifestations of such an allergy in a family is referred to as atopic hypersensitivity reaction. The antigen is often called an allergen. The specific allergen may be a food, a chemical, pollen from a plant, or a drug. One person may be allergic to a number of substances, and these may change over time. Common allergenic foods include shellfish, nuts, and strawberries. Hypersensitivities occur frequently with drugs such as ASA (aspirin), penicillin, sulfa, and local anesthetics. Cross-allergies are common; therefore an allergy to one form of penicillin means that an individual is likely allergic to all drugs in the penicillin family. There has been a significant increase in the number of children who experience severe type 1 hypersensitivity reactions. Most of these reactions occur when the child is exposed to a particular food, such as peanuts or other members of the legume family. The reactions may be severe enough to result in anaphylaxis. Once diagnosed, the child carries an emergency injector or EpiPen, which can be administered to prevent severe anaphylaxis resulting in bronchospasm and hypovolemia.

Type I: Allergic Reactions

active artificial immunity develops when a specific antigen is purposefully introduced into the body, stimulating the production of antibodies. For example, a vaccine is a solution containing dead or weakened (attenuated) organisms that stimulate the immune system to produce antibodies but does not result in the disease itself. Work continues on the development of vaccines using antigenic fragments of microbes or genetically altered forms.

active artificial immunity

immunity is acquired 4 ways. Active immunity develops when the persons own body developed antibodies or t cells in response to a specific antigen introduced into the body. This process takes a few weeks, but the result usually lasts for years because memory b and t cells are retained in the body.

active immunity

active natural immunity may be acquired by direct exposure to an antigen, for example, when a person has an infection and then develops antibodies

active natural immunity

tissue transferred between members of the same species but may differ genetically; e.g., one human to another human

allograft (homograft)

anaphylaxis is a severe, life-threatening systemic hypersensitivity reaction resulting in decreased blood pressure, airway obstruction, and severe hypoxia. Commonly caused by exposure to latex materials such as gloves, insect stings, ingestion of nuts or shellfish, administration of penicillin, or local anesthetic injections, the reaction usually occurs within minutes of the exposure.

anaphylaxis or anaphylactic shock

antibodies are a specific class of proteins termed immunoglobulins. Each has a unique sequence of amino acids (variable portion, which binds to antigen) attached to a common base (constant region that attaches to macrophages). Antibodies bind to the specific matching antigen, destroying it. This specificity of antigen for antibody, similar to a key opening a lock, is a significant factor in the development of immunity to carious diseases. Antibodies are found in the general circulation, forming the globulin portion of the plasma proteins, as well as in the lymphoid structures. Immunoglobulins are divided into five classes, each of which has a special structure and function. Specific immunoglobulins may be administered to treat diseases such as Guillain-Barre syndrome an autoimmune disease that attacks the peripheral nervous system that can cause progressive paralysis.

antibodies or immunoglobulins

specific protein produced in humoral response to bind with antigen

antibody

foreign substance, microbes or component of cell that stimulates immune response

antigen

immunosuppression techniques are used to reduce the immune response and prevent rejection. The common treatment involves drugs such as cyclosporine, azathioprine (Imuran), and prednisone, a glucocorticoid. The drugs must be taken on a continuous basis and the patient monitored for signs of rejection. The use of cyclosporine has been very successful in reducing the risk of rejection, but the dosage must be carefully checked to prevent kidney damage. Many new drugs are also under investigation in clinical trials. The major concern with any immunosuppressive drug is the high risk of infection, because the normal body defenses are now limited. infections are often caused by opportunistic microorganisms, microbes that usually are harmless in healthy individuals. Persons with diabetes frequently require transplants of kidneys and other tissues, and this group of patients is already at risk for infection because of vascular problems. Loss of the surveillance and defense functions of the immune system has also led to increased risk of lymphomas, skin cancers, cervical cancer, and colon cancer in those taking antirejection drugs. Dental professionals should be aware of the high incidence of gingival hyperplasia in patients taking cytosporine.

antirejection drugs and effects

vaccine (live or attenuated organisms) is injected into the person. No illness results, but antibodies form. Memory cells created. Example- person has measles vaccine and gains immunity

artificial active

antibodies injected into a person (antiserum) to provide temporary protection or minimize severity of infection. Memory cells are not created. Example- Gamma-globulin if recent exposure to microbe

artificial passive

a lung disorder, asthma may result from an allergic response in the bronchial mucosa that interferes with airflow. Frequently a triad of atopic conditions including hay fever, eczema, and asthma occurs in family histories.

asthma

eczema or atopic dermatitis is a chronic skin condition, often with a genetic component, common in infants and young children. The skin rash may occur on the face, trunk, or extremities. It is associated with ingested foods, irritating fabrics, and a dry atmosphere. There may be remissions as the child develops, but the condition may recur in adulthood.

atopic dermatitis or eczema

antibodies against self-antigen; attacks body's own tissues

autoantibody

tissue transferred from one part of the body to another part on the same individual; e.g., skin or bone

autograft

the b lymphocytes or b cells are responsible for humoral immunity through the production of antibodies or immunoglobulins. B cells are thought to mature in the bone marrow and then proceed to the spleen and lymphoid tissue. After exposure to antigens, and with the assistance of t lymphocytes, they become antibody-producing plasma cells. B lymphocytes act primarily against bacteria and viruses that are outside body cells. B memory cells that provide or repeated production of antibodies also form in humoral immune responses.. NK cells are lymphocytes distinct from the t and b lymphocytes. they destroy, w/o any prior exposure and sensitization, tumor cells and cells infected with viruses.

b cells and NK cells

biological warfare and bioterrorism use biological agents to attack civilians or military personnel. Concern continues about the possibility of bioterrorism using altered antigenic forms of common viruses or bacteria. Such bioweapons would have widespread impact on populations because current immunizations do not protect against such agents. It is important to recognize that large outbreaks of diseases formerly controlled by vaccines may represent acts of bioterrorism. Such outbreaks should be reported to the local authorities as soon as they are recognized.

bioterrorism

Type I hypersensitivity begins when an individual is exposed to a specific allergen and for some reason develops IgE antibodies from B lymphocytes. These antibodies attach to mast cells in specific locations creating sensitized mast cells. Mast cells are connective tissue cells that are present in large numbers in the mucosa of the respiratory and digestive tracts. On re-exposure to the same allergen, the allergen attaches to the IgE antibody on the mast cell, stimulating the release of chemical mediators such as histamine from the granules within the mast cells. These chemical mediators cause an inflammatory reaction involving vasodilation and increased capillary permeability at the site (e.g., the nasal mucosa), resulting in swelling and redness of the tissues.This initial release of histamine also irritates the nerve endings, causing itching or mild pain.

causative mechanism

lymphoblasts from bone marrow stem cells go to the thymus, then from the thymus comes t cells that migrate to the lymph nodes then from the lymph nodes travel to the antigen and begin antigen stimulation and circulate various types of sensitized t cells such as helper t cells, memory t cells, suppressor t cells, and cytotoxic t cells.

cell mediated immunity

WBCs: bind IgE, release histamine in anaphylaxis

cells: Basophils

WBCs: participate in allergic responses and defense against parasites

cells: Eosinophils

natural killer cells destroy foreign cells, virus-infected cells, and cancer cells

cells: NK lymphocytes

white blood cells: cell-mediated immunity

cells: T lymphocytes

humoral immunity-activated cell becomes an antibody-producing plasma cell or a B memory cell

cells: b lymphocytes

destroy antigens, cancer cells, virus-infected cells

cells: cytotoxix or killer T cells

activate b and t cells; control or limit specific immune response

cells: helper t cells

Phagocytosis; process and present antigens to lymphocytes for the immune response

cells: macrophages

release chemical mediators such as histamine in connective tissue

cells: mast cells

remember antigen and quickly stimulate immune response on reexposure

cells: memory t cells

WBCs: migrate from the blood into tissues to become macrophages

cells: monocytes

WBCs for phagocytosis; nonspecific defense; active in inflammatory response

cells: neutrophils

develop from B lymphocytes to produce and secrete specific antibodies

cells: plasma cells

cause vasodilation, increased permeability (edema), and pain

chemcal mediators: kinins (e.g., bradykinin)

a number of chemical mediators such as histamine or interleukins may be involved in an immune reaction, depending on the particular circumstances. These chemicals have a variety of functions, such as signaling a cellular response or causing cellular damage.

chemical mediators

attract phagocytes to area of inflammation

chemical mediators: chemotactic factors

group of inactive proteins in the circulation that, when activated, stimulate the release of other chemical mediators, promoting inflammation, chemotaxis, and phagocytosis

chemical mediators: complement

includes lymphokines, monokines, interferons, and interleukins; produced by macrophages and activated T-lymphocytes; stimulate activation and proliferation of B and T cell, communication between cells; involved in inflammation, fever, and leukocytosis

chemical mediators: cytokines (messengers)

released from mast cells and basophils, particularly in allergic reactions. Causes vasodilation and increased vascular permeability or edema, also contraction of bronchiolar smooth muscle, and pruritus

chemical mediators: histamine

group of lipids, derived from mast cells and basophils, which cause contraction of bronchiolar smooth muscle and have a role in development of inflammation

chemical mediators: leukotrienes

group of lipids with varying effects. Some cause inflammation, vasodilation and increased permeability, and pain

chemical mediators: prostaglandins

a cytokine active in the inflammatory and immune responses; stimulates fever, chemotaxis, meddiator of tissue wasting, stimulates T cells, mediator in septic shock (decreasing blood pressure), stimulates necrosis in some tumors

chemical mediators: tumor necrosis factor (TNF)

it now appears that neonates and young infants can receive heart transplants from donors without a good tissue match. Rejection does not occur because the infant's immune system is not yet mature and does not respond to foreign tissue. The long-terms effects are not known, but the results to date are encouraging. Because heart transplants in infants are limited by organ size as well as organ availability, the removal of the HLA restrictions would make more heart transplants available when needed and more donor hearts could be used rather than wasted,

children who receive heart transplants

the signs and symptoms of an allergic reaction occur on the second or any subsequent exposure to the specific allergen because the first exposure to the allergen causes only the formation antibodies and sensitized mast cells. The target area becomes red and swollen, there may be vesicles or blisters present, and usually the area is highly pruritic or itchy.

clinical signs and symptoms

the compliment system is frequently activated during an immune reaction with IgG or IgM class immunoglobulins. Complement involves a group of inactive proteins, numbered C1 to C9, circulating in the blood. When an antigen-antibody complex binds to the first complement component, C1, a sequence of activating steps occurs (similar to a blood clotting cascade). Eventually this activation of the complement system results in the destruction of the antigen by lysis when the cell membrane is damaged, or some complement fragment may attach to a microorganism, marking it fot phagocytosis. Complement activation also initiates an inflammatory response.

complement system

many new and improved techniques are emerging, and more details on these details on these techniques may be found in reference works on serology or diagnostic methods.Tests may assess the levels and functional quality (qualitative and quantitative) of serum immunoglobulins or the titer (measure) of specific antibodies. Identification of antibodies may be required for such purposes as detecting Rh blood incompatibility (indirect Coombs test) or screening for HIV infection (by enzyme-linked immunosorbent assay [ELSA]). Pregnant women are checked for levels of antibodies, particularly for German measles to establish their potential for complications if they are exposed to this disease while pregnancy which could result in fetal death. During hepatitis B infection, changes in the levels of antigens and antibodies take place, and these changes can be used to monitor the course of the infection and level of immunity. The number and characteristics of the lymphocytes in the circulation can be examined as well. Extensive HLA (MHC) typing is required to complete tissue matching before transplant procedures.

diagnostic tests

emerging infectious diseases are those newly identified in a population. Re-emerging infectious diseases were previously under control but unfortunately not all individuals participate in immunization programs; therefore infectious disease outbreaks persist. These infectious diseases are on the rise due to globalization, drug resistance, and many other factors.

emerging and re-emerging infectious diseases and immunity

food allergies may be manifested in several ways. When an inflammatory reaction occurs in the mucosa of the digestive it results in nausea, vomiting, and/or diarrhea. In some cases, food allergies may cause a rash on the skin called hives, which are large, hard, raised red masses that are highly pruritic. In severe cases, these hives also occur on the pharyngeal mucosa and may obstruct airflow; therefore it is important to watch for respiratory difficulty associated with any allergenic skin rash.

food allergies

an allergic reaction to the nasal mucosa causes frequent sneezing, copious watery secretions from the nose, and itching. Because the nasal mucosa is continuous with the mucosa of the sinuses and the conjunctiva of the eyelid, the eyes are frequently red, watery, and pruritic as well. Hay fever, or allergic rhinitis, is usually seasonal because it is related to plant pollens in the air, but some people are susceptible to multiple allergens such as molds or dusts and can exhibit signs at any time of yr.

hay fever or allergic rhinitis

lymphoblasts from bone marrow stem cells go to the bone marrow and then activate b cells which migrate to the lymph nodes and then travel to the antigen to begin antigen stimulation which produce memory be cells and anitbodies, which have binding sites for specific antigens, a variable region and a constant region.

humoral or antibody-mediated immunity

hypersensitivity or allergic reactions are unusual and perhaps damaging immune responses to normally harmless substances. These reactions stimulate the inflammatory response. There are four basic types of hypersensitivities, which differ in the mechanism causing tissue injury. The world allergy organization has developed a standard nomenclature to identify allergic problems and differentiate them from similar conditions; for example, allergic rhinitis, allergic asthma, and allergic contact dermatitis.

hypersensitivity reactions

a long list of vaccines is available, including those for protection against polio, diphtheria, measles, and chickenpox. Infants begin a regular schedule of immunizations/vaccines shortly after birth to reduce the risk of serious infections and in hopes of eradicating some infectious diseases. Immunization recommendations for all age groups are published by the CDC. A toxoid is an altered or weakened bacterial toxin that acts as an antigen in a similar manner. A booster is an additional immunization given perhaps 5 or 10 yrs after initial immunization that reminds the immune system of the antigen and promotes a more rapid and effective secondary response. Booster immunization are currently used for tetanus.

immunizing/vaccinations/boosters

in type II hypersensitivity, often called cytotoxic hypersensitivity, the antigen is present on the cell membrane. the antigen may be a normal body component or foreign. Circulating IgG antibodies react with the antigen, causing destruction of the cell by phagocytosis or by releasing cytolytic enzymes related to complement activation. An example of this reaction is the response to an incompatible blood transfusion. A person with type

incompatible blood transfusions

tissue transferred between two genetically identical bodies; e.g., identical twins

isograft

The primary cell in the immune response is the lymphocyte, one of the leukocytes or WBCs produced by the bone marrow. Mature lymphocytes are termed immuno-competent cells-cells that have the special function of recognizing and reacting with antigens in the body. The two groups of lymphocytes, B and T, determine which type of immunity will be initiated, either cell-mediated (B) or humoral (T) immunity.

lymphocytes b and t

pathogens enter the body and cause illness; antibodies form in host. memory cells created. example- a person has chicken pox once

natural active

antibodies passed directly from mother to child to provide temporary protection. Memory cells are not created. Example- placental passage during pregnancy or ingestion of breast milk

natural passive

the occurrence of many infectious diseases, such as polio and measles, has declined where vaccination rates have been high, creating herd immunity- a phenomenon in which a high percentage of a population in vaccinated, thus decreasing the chances of acquiring and spreading an infectious disease. Believing smallpox (variola) had been eradicated in many countries by the mid-1950s, the US discontinued the smallpox vaccine in 1972. The WHO worked toward worldwide eradication and the last case of naturally occurring smallpox was recorded in 1977. Polio vaccination was implemented in 1954, and cases are a rare occurrence today in developed areas of the world. Recent outbreaks of measles and mumps in North America are the result of inadequate revaccination of teens. The search continues for additional vaccines against AIDS and malaria, tuberculosis, and other widespread infections. Research is also continuing on genetic vaccines, in which only a strand of bacterial DNA forms the microorganism itself. Immunotherapy is an expanding area of cancer research in the search for new and more specific therapies.

outcome of infectious disease

passive immunity occurs when antibodies are transferred from one person to another. These are effective immediately, but offer only temporary protection because memory has not been established in the recipient, and the antibodies are gradually removed from the circulation . There are also two forms of passive immunity: passive natural immunity occurs when IgG is transferred from mother to fetus across the placenta. Breast milk also supplies maternal antibodies. These antibodies protect the infant for the first few months of life. passive artificial immunity results from the injection of antibodies from a person or animal into a second person.An example is the administration of rabies antiserum or snake antivenom. Sometimes immunoglobulins are administered to an individual who has been exposed to an organism but has not yet been immunized to reduce the effects of the infection (for example, hepatitis B)

passive natural and passive artificial immunity

large amounts of chemical mediators are released from mast cells into the general circulation very quickly, resulting in two serious problems. General or systemic vasodilation occurs with a sudden, severe decrease in BP. In the lungs, edema of the mucosa and constriction of the bronchi and bronchioles occur, obstructing airflow. The marked lack of oxygen that results from both respiratory and circulatory impairment causes loss of consciousness within minutes.

pathophysiology

a primary response occurs when a person is first exposed to an antigen. During exposure, the antigen is recognized and processed, and subsequent development of antibodies or sensitized t cells is initiated. This process usually takes 1 to 2 weeks and can be monitored by testing serum antibody titer. Following the initial rise in seroconversion the level of antibody falls.

primary response in immunity

rejection is a complex process, primarily involving a type 4 cell mediated hypersensitivity reaction, but also involving a humoral response, both of which cause inflammation and tissue necrosis. The rejection process eventually destroys the organ, so that transplanted organs often must be replaced after a few yrs. Survival time of a transplant is increased when the HLA match is excellent, the donor is living (less risk of damage to donor tissue), and immunosuppressive drugs are taken on a regular basis. Corneas and cartilage lack a blood supply; therefore rejection is not a problem with these transplanted tissues. With improved surgical techniques and better drug therapy, transplants are now lasting a longer time and significantly prolonging the recipient's life.

rejection process

secondary response results when a repeat exposure to the same antigen occurs. this response is much more rapid and results in higher antibody levels than the primary response. Even yrs later the memory cells very quickly stimulate production of large numbers of the matching antibodies or t cells.

secondary response in immuntiy

other chemical mediators, including prostaglandins and leukotrienes, are released at the site in a second phase of the reaction, and these cause similar effects. If the sensitized mast cells are located in the nasal mucosa, the antigen-antibody reaction causes the typical signs of hay fever. If sensitization occurs in the respiratory mucosa in the lungs, the chemical mediators also cause bronchoconstriction (contraction of the bronchiolar smooth muscle and narrowing of the airway) and release of mucus in the airways, resulting in obstruction of the airways, or asthma.

sensitization in the nasal and respiratory mucosa

the initial manifestations of anaphylaxis include a generalized itching or tingling sensation over the body, coughing, and difficulty in breathing. This is quickly followed by feelings of weakness, dizziness, or fainting, and a sense of fear and panic. Edema may be observed around the eyes, lips, tongue, hands, and feet. Hives, or urticaria, may appear on the skin. General collapse soon follows w/a loss of consciousness, usually within minutes.

signs and symptoms

when a single strain of bacteria or virus causes a disease, the affected person usually has only one episode of the disease because the specific antibody is retained in the memory. Young children are subject to many infections until they establish a pool of antibodies. As one ages, the number of infections declines. However, when there are many strains of bacteria or viruses causing a disease, for example, the common cold (which has more than 200 causative organisms, each with slightly different antigens), an individual never develops antibodies to all the organisms, and therefore has recurrent colds. The influenza virus, which affects the respiratory tract, has several antigenic forms, for example, type A and type B. These viruses have various strains that mutate or change slightly over time. For this reason, a new influenza vaccine is manufactured each yr, its composition based on the current antigenic forms of the virus most likely to cause an epidemic of the infection.

strains of viruses or bacteria

t cells arise from stem cells, which are completely differentiated celld held in reserve in the bone marrow and then travel to the thymus for further differentiation and development of cell membrane receptors. cell-mediated immunity develops when t cells with protein receptors on the cell surface recognize antigens on the surface of target cells and directly destroy the invading antigens. These specially programmed t cells then reproduce, creating an "army" to battle the invader, and they also activate other t and b cells. t cells are primarily effective against virus-infected cells, fungal and protozoal infections, cancer cells, and foreign cells such as transplants. There are a number of subgroups of t cells, which has a specialized function in the immune response. The cytotoxic CD8 positive t-killer cells destroy the target cell by binding to the antigen and releasing damaging enzymes or chemicals, such as monokines and lymphokines, which may destroy foreign cell membranes or cause an inflammatory response, attract macrophages to the site, stimulate the proliferation of more lymphocytes, and stimulate hematopoiesis. Phagocytic cells then clean up the debris. The helper CD4 positive t cell facilitates the immune response. A subgroup, the memory t cells, remains in the lymph nodes for yrs, ready to activate the response again if the same invader returns.

t cells

Because of unique antigens, often a protein, on the surface of an individuals cells, that a persons immune system can distinguish self from non-self (foreign) and can thus detect and destroy unknown material. Normally the immune system ignores self cells, demonstrating tolerance. When the immune system recognizes a specific non-self antigen as foreign, it develops a specific response to that particular antigen and stores that particular response in its memory cells for future reference if the antigen reappears in the body. It is similar to a surveillance system warning of attack and the subsequent mobilization of an army for defense. For example, lymphoid tissue in the pharynx, such as tonsils and adenoids, can capture antigens in material that is inhaled or ingested and process the immune response. Note that a person must have been exposed to the specific immunity to it (such as antibodies) before this defense is effective. This response is usually repeated each time the person is exposed to a particular substance (antigen) because the immune system has memory cells. Immune responses that occur after the first introduction of the antigen are usually more rapid and intense than the initial response. In destroying foreign material, the immune system is assisted by nonspecific defense mechanisms such as phagocytosis and the inflammatory response. By removing the foreign material, the immune system also plays a role in preparing injured tissue for healing. When the plasma membrane of malignant neoplastic cells is abnormal, the immune system may be able to identify these cells as foreign and remove them, thus playing an important role in the prevention of cancer. It has been noted that individuals frequently develop cancer when the immune system is depressed as with an infection or increased stress. However, not all cancer cells are identifiable as foreign; therefore the immune system may not remove them. The immune system directs the response to an antigen, but also has built-in controls to prevent excessive response. Two limiting factors are the removal of the causative antigen during the response, and the short lifespan of the chemical messengers. Tolerance to self-antigens prevents improper responses

the immune response

natural immunity is species specific. For example, humans are not usually susceptible to infections common to many other animals. Innate immunity is gene specific and is related to ethnicity, as evident from the increased susceptibility of North American aboriginal people to tuberculosis.

the process of acquiring immunity

replacement of damaged organs or tissues by healthy tissues from donors is occurring more frequently as the success of such transplants improves. Skin, corneas, bone, kidneys, lungs, hearts, and bone marrow are among the more common transplants. Transplants differ according to donor characteristics. In most cases transplants, or grafts, involve the introfuction of foreign tissue from one human, the donor, into the body of the human recipient (allograft). Because the genetic makeup of cells is the same only in identical twins, the obstacle to complete success of transplantation has been that the immune system of the recipient responds to the HLAs (MHCs) in foreign tissue, rejecting and destroying the graft tissue.

tissue and organ transplant rejection

it is essential that epinephrine injection be administered immediately. This acts in the same way as the natural hormone epinephrine. Antihistamine drugs (diphenhydramine [benadryl] or chlorpheniramine [chlor-Trimenton]) are useful in the early stages of an allergic reaction because they block the response of the tissues to the released histamine (blocking histamine- 1 receptors on cells). Glucocorticoids or cortisone derivatives may be used for severe or prolonged reactions because they reduce the immune response and stabilize the vascular system. Glucocorticoids can be administered by injection or by mouth, or they can be applied topically to the skin.

treatment by epinephrine and other antihistamine drugs/glucocorticoids

skin tests can be performed to determine the specific cause of an allergy. This procedure involves scratching the skin and dropping a small amount of purified antigen on the scratch. The site is observed for erythema or redness, which indicates a positive skin reaction. In many cases, the person with an allergy can determine the contributing factors by observation and keep a log of daily exposure to foods, pollens, and other allergens. Avoidance of the suspected antigen will keep the person symptom free. Desensitization treatments involving repeated injections of very small amounts of antigen to create a blocking antibody may reduce the allergic response.

treatment by tests

IgG or IgM reacts with antigen on cell. complement activated. Causes cell lysis and phagocytosis

types of hypersensitivities: ABO bloodincompatibility

antigen-antibody complex deposits in tissue. complement activated. Causes inflammation and vasculitis

types of hypersensitivities: Autoimmune disorders: SLE, glomeruloenphritis

antigen binds to t lymphocyte; sensitized lymphocyte releases lymphokines. Causes delayed inflammation

types of hypersensitivities: contact dermatitis: transplant rejection

IgE bound to mast cells; release of histamine and chemical mediators. causes immediate inflammation and pruritis

types of hypersensitivities: hay fever; anaphylaxis

tissue transferred from one member of one species to a different species; e.g., pig to human

xenograft (heterograft)