exam 3 merge

Receptors have the capacity

to respond to a nearly infinite number of unique antigens

Autoimmune diseases:

• individuals actually develop hypersensitivity to themselves -Autoantibodies, T cells, or both mount an abnormal attack against self antigens. -Systemic: involves several major organs -Organ specific: involves only one organ or tissue

When challenged with antigen, both B and T cells proliferate and differentiate:

-A clone, or group of genetically identical cells, are created. -Some clones are memory cells that will ensure the future reactivity to a specific antigen. -B and T cell responses differ.

Tuberculin reaction

-Also known as the purified protein derivative(PPD) test. -Acute skin inflammation at the injection site following an extract of Mycobacterium tuberculosis. -Similar skin reactions occur with leprosy, syphilis, histoplasmosis, toxoplasmosis, and candidiasis. -TH1 cells release cytokines and recruit macrophages, neutrophils and eosinophils to the site, causing a red bump.

Superantigens

-Bacterial toxins that are potent stimuli for T cells -Activate T cells at a rate 100 times greater than ordinary signals -The result can be an overwhelming release of cytokines and cell death Toxic shock syndrome and certain autoimmune diseases are associated with superantigens

Alloantigens

-Cell surface markers and molecules that occur in some members of the same species, but not in others -The basis for an individual's blood group and major histocompatibility profile -Responsible for incompatibilities that can occur in blood transfusion or organ grafting

All cells have a variety of different markers on their surfaces for

-Detection -Recognition -Cell communication •These markers play an important role in activating different components of the immune system.

Principal stages of immunologic development and interaction

-Lymphocyte development and differentiation -Presentation of antigens -Challenge of B (bursa of Fabricius) and T cells by antigens -T-lymphocyte response: cell-mediated immunity -B-lymphocyte response: production and activities of antibodies

•Type of antigens include:

-Proteins and polypeptide: enzymes, cell surface structures, and exotoxins -Lipoproteins: cell membrane -Glycoproteins: blood cell markers -Nucleoproteins: DNA complexed to proteins, but not pure DNA -Polysaccharides (certain bacterial capsules) -Lipopolysaccharides

Most recognized infection-induced immunodeficiency is AIDS

-T helper cells, monocytes, macrophages, and antigen-presenting cells infected by HIV -Depletion of T-helper cells and impairment of immune responses account for cancers and opportunistic infections caused by AIDS.

Antibodies produced against the chickenpox virus will not function against the

-rush to the attack once again.

Pertaining to Type II Hypersensitivity reactions, which of the following is/are true?

A.Hemolytic disease of the newborn is an example of this type of hypersensitivity. B.It involves IgG and IgM C.Transfusion reactions are examples. D.A and B are the only true statements. E.A, B and C are all true statements.

Type I hypersensitivity involves all of the following except

A.IgE B.Mast cells and basophils C.Immediate responses D.Previous exposure to the allergen E.All of the above are involved

Which of the following is not an IgE and/or mast-cell-mediated allergic condition? A.Asthma B.Food allergy C.Systemic lupus erythematosus D.Allergy to penicillin E.Eczema

A.Systemic lupus erythematosus

The most common deficiency in immunoglobulins is _____ deficiency

A.gA

For each of the properties listed, determine if it describes a T cell or a B cell: A.Matures in the bone marrow B.High numbers of cells circulating in the blood C.Require antigen to be presented with an MHC molecule D.Produce antibodies Cells activated to help other immune cells, suppress or kill abnormal cells, etc

Answer: A. B cell, B. T cell, C. T cell, D. B cell, E. T cell

Which of the following antibody types is not involved in serum sickness or the Arthus reaction? A.IgA B.IgE C.IgG D.IgM E.All of the choices are involved.

Answer: B. IgE is involved in anaphylaxis. All of the rest are involved in immune complex diseases.

Which of the following is not an IgE and/or mast-cell-mediated allergic condition? A.Asthma B.Food allergy C.Systemic lupus erythematosus D.Allergy to penicillin Eczema

Answer: C. Systemic lupus erythematosus

Which of the following is not an antigen-presenting cell: A.Macrophage B.Dendritic cell C.T-helper cell D.B cell E.All of the choices are antigen presenting cells.

Answer: C. T-helper cells

Which of the following is not a result of an abnormal or undesirable immune function? A.Asthma B.Anaphylaxis C.Contact dermatitis D.Fever Lupus

Answer: D. Fever

When is the RhoGAM shot needed? A.Rh+ mother, Rh+ fetus B.Rh+ mother, Rh- fetus C.Rh- mother, Rh- fetus D.Rh- mother, Rh+ fetus E.All of the choices are correct. The mother always responds to the fetus as foreign tissue and mounts an immune response against it.

Answer: D. The Rh- mother's immune system sees the Rh antigen on the RBCs of the fetus and mounts an immune response against them.

B cells mature in the ________ and T cells mature in the _______. Both cell types then migrate to the ________ and ________. A.spleen, lymph nodes; bone marrow, thymus B.thymus, bone marrow; tonsils, GALT C.GALT, tonsils; Peyer's patches, lymph vessels D.bone marrow, thymus; lymph nodes, spleen E.thymus, bone marrow; lymph vessels, blood

Answer: D. bone marrow, thymus, lymph nodes, spleen

The two type of cells that undergo selective process that prepares them for reacting only to one specific antigen or immunogen

B and T lymphocytes

lymphocyte development

B cells mature in bone marrow T cells mature in thymus All lymphocytes arise from the same basic stem cell type

examples of haptens

Examples -Drugs -Metals -Ordinarily innocuous household, industrial, and environmental chemicals Many haptens develop antigenicity in the body by combining with large carrier molecules such as serum proteins

An antigen is a

Foreign molecules that stimulate an immune response Unlike PAMPs, antigens are highly individual and stimulate specific immunity Unlike PAMPsUnlike PAMPs

The three functional types of T cells are as follows:

Helper T cells Regulatory T cells Cytotoxic T cells

Lymphocyte Receptors

Major role is to "accept" or "grasp" antigens in some form

Hyposensitivity Classification Primary

Primary •Mostly genetics - congenital •Less common -Thymic aplasia (DiGeorge syndrome): genetic defects of the thymus -severe combined immunodeficiency (SCID), which is known as alymphocytosis or "boy in a bubble" disease

Cytotoxic T (TC) Cells: Cells that Kill Other Cells

Target cells that TC cells can destroy include: -Virally infected cells: recognize virus peptides displayed on the cell surface -Cancer cells: TC constantly survey the tissues and immediately attack any abnormal cells they encounter -Cells from other animals and humans: the most important factor in graft rejection

The Immune Response:A Two-Sided Coin

The human immune system is powerful and intricate, having the potential to cause injury and disease. Defects in the immune system can range from hay fever to dermatitis. Abnormal or undesirable immune functions can result in: -Asthma -Anaphylaxis -Diabetes -Rheumatoid arthritis -Graft rejection

The Major Histocompatibility Complex (MHC)

These are a set of genes that codes for human cell markers or receptors -Found on all cells except red blood cells -Also known as the Human Leukocyte Antigen (HLA) system -These markers play a vital role in recognition of self by the immune system and in rejection of foreign tissue.

Helper T cells

activate macrophages, assist B-cell processes, and help activate cytotoxic T cells

Any exposed or released protein or polysaccharide is potentially an

antigen

Allergens

antigens that evoke allergic reactions, discussed in chapter 14

Regulatory T cells:

control the T-cell response

T cells secrete

cytokines to help destroy pathogens, but they do not produce antibodies

T cells receptors

have receptors that bind antigens that have been processed and complexed with MHC molecules on the presenting cell surface such as macrophages and neutrophil

MHCs

is a form of Role of Markers and Receptors Major Histocompatibility Complex molecules, specialized cell surface proteins on the surface of all vertebrate cells, phagocytes for example displays fragments of a pathogen's proteins by binding it to MHC proteins on its surface, allows T cells to recognize proteins and MHC but T cells cannot differentiated between the protein and the MHCs

epitope

is the region on an antigen that antibodies of lymphocytes bind to.

Cytotoxic T cells

lead to the destruction of infected host cells and other "foreign" cells

B cells

mature in specialized bone marrow sites. - First discovered in birds in the bursa fabricius

T cells

mature in the thymus, cell mediated immunity

Antigens or immunogens

molecules that stimulate a response by B and T cells there proteins or polysaccharide molecules on or inside cells and viruses

B cells have

receptors that bind antigens.

Two features that characterize the specific immune response are

specificity and memory

Immunocompetence

the ability of the body to react with countless foreign substances

Type II Hypersensitivities: Reactions That Lyse Foreign Cells

•A complex group of syndromes that involve complement-assisted destruction (lysis) of cells by antibodies (IgG and IgM) directed against those cells' surface antigens: -Transfusion reactions -Some types of autoimmunities •Alloantigens: -Molecules that differ in the same species that are recognized by the lymphocytes of the recipient -Not an immune dysfunction; the immune system is functioning normally by reacting to foreign cells in an organ or tissue transplant

Specific Immunity: The Third and Final Line of Defense

•Adaptive or learn immunity acquired only after an immunizing event such as an infection

Antigen Epitopes

•All antigens have one or more epitopes -The portion of an antigenic molecule to which a lymphocyte responds or where antibodies bind to the antigen. -These binding sites are also called antigenic determinant -Primary signal to the immune system that the molecule is foreign

The Nature of Allergens and Their Portals of Entry

•Allergens have certain immunogenic characteristics: -Proteins are more allergenic than carbohydrates, fats, or nucleic acids -Haptens: nonproteinaceous substances with a molecular weight of less than 1,000 that can form complexes with carrier molecules in the body -Organic and inorganic chemicals found in industrial and household products, cosmetics, food, and drugs are haptens.

Who Is Affected?

•Allergists estimate that 10 - 30% of the population is prone to atopic allergy. Self-treatment with over-the-counter medications makes this a low estimate. •Type I allergies: -Relatively mild -Asthma and anaphylaxis may require hospitalization and can cause death. -Some allergies last for a lifetime, some are "outgrown," others develop later in life.

Type I Allergic Reactions: Atopy and Anaphylaxis

•Allergy vs. Hypersensitivity: -Allergy: exaggerated immune response that is manifested by inflammation -Hypersensitivity: delayed reactions •Allergens: innocuous substances that induce allergy in sensitive individuals •Atopy: chronic local allergy such as hay fever or asthma •Anaphylaxis: systemic, sometimes fatal reaction that involves airway obstruction and circulatory collapse

Secondary Immunodeficiency Diseases (cont'd) 2

•An ironic outcome of lifesaving medical procedures is the suppression of the immune system: -Drugs that prevent graft rejection can also suppress beneficial immune responses. -Radiation and anticancer drugs are damaging to the bone marrow and other body cells.

Anaphylaxis: An Overpowering IgE-Mediated Allergic Reaction

•Anaphylaxis/anaphylactic shock: -Cutaneous anaphylaxis: wheal-and-flare inflammatory reaction to the local injection of allergen -Systemic anaphylaxis: characterized by sudden respiratory and circulatory disruption that can be fatal within minutes due to airway blockage -Bee stings and injection of antibiotics or serum are most commonly implicated -Result of the sudden, massive release of chemicals into the tissues and blood, which act rapidly on target organs

Antigens

•Antigens are molecules capable of inducing an immune response or cause the body to produce antibodies.

Taking Drugs to Block Allergy (cont'd)

•Antihistamines: -Most widely used medications for preventing symptoms of atopic allergy -Bind to histamine receptors on target organs •Aspirin and acetaminophen: reduce pain by interfering with prostaglandins •Theophylline: bronchodilator that reverses spasms in respiratory smooth muscles Epinephrine (adrenaline):reverses constriction of airways and slows the release of allergic mediators

Types of Immune Complex Disease

•Arthus reaction and serum sickness are associated with certain types of passive immunization. •Similar to anaphylaxis in that all require sensitization and preformed antibodies •Differences from anaphylaxis: -Depend on IgG, IgM, or IgA rather than IgE -Require large doses of antigen -Symptoms are delayed hours to days

Hyposensitivity Classification Secondary

•As a result of complications to diseases, infestations, chemotherapy, side effects • HIV

Severe Combined Immunodeficiencies (SCIDs - cont'd)

•As a result of mutations in several genes. •Usually leads to severe defects in T and B lymphocytes. •SCID children require rigorous aseptic techniques to protect them from opportunistic infections: -David Vetter: lived his life in a sterile plastic bubble •Only serious option for longtime survival is total replacement or correction of lymphoid cells: -Infants can benefit from fetal liver or stem cell grafts -X-linked and ADA (Adenosine deaminase deficiency) types of SCID can be treated with gene therapy; insertion of normal genes to replace the defective genes

Classes of Grafts

•Autograft: tissue transplanted from one site on an individual's body to another site •Isograft: tissue from an identical twin is used •Allograft: exchanges between genetically different individuals belonging to the same species; the most common types of grafts •Xenograft: a tissue exchange between individuals of a different species

Treatment and Prevention of Allergy

•Avoid the allergen, although this may be difficult in many instances. •Take drugs that block the action of lymphocytes, mast cells, or chemical mediators. Use injections that short-circuit the allergic reaction

T-Cell Receptors

•Belongs to the same family as the B-cell receptor •Similar to B cells: -Formed by genetic recombination -Has variable and constant regions -Inserted into membrane -Has an antigen binding site •Relatively small and never secreted

Types of Transplants (cont'd)

•Bone marrow transplantation: -Used in individuals with immune deficiencies, aplastic anemia, leukemia, and other cancers -Patient is treated with chemotherapy and whole-body irradiation to destroy their own blood cells, preventing rejection. -Closely matched donor marrow is infused. -GVHD can still occur, and antirejection drugs may be necessary. -After transplantation, a recipient's blood type may change to the blood type of the donor.

T cells and B cells both

•Both cell types migrate to separate areas of lymphoid organs.

Secondary Immunodeficiency Diseases (cont'd)

•Cancers that target the bone marrow can be responsible for malfunction of humoral and cellular immunity: -Leukemia: cancer cells outnumber normal cells, displacing them from bone marrow and blood -Plasma cell tumors: produce large amounts of nonfunctional antibodies -Thymus gland tumors: cause severe T-cell deficiencies

Contact Dermatitis

•Caused by exposure to resins in poison ivy and poison oak, haptens in household and personal articles, and drugs •Requires a sensitizing dose followed by a provocative dose. •Allergen penetrates the outer skin layers: -Processed by skin dendritic cells and presented to T cells -Subsequent exposures attract lymphocytes and macrophages. -Cells release enzymes and cytokines that damage the epidermis and vicinity.

Secondary Immunodeficiency Diseases

•Caused by one of four general agents: -Infection -Organic disease -Chemotherapy -Radiation

Stages III and IV: T-Cell Response

•Cell-Mediated Immunity (CMI): -T-cell reactions are the most complex and diverse in the immune system and involve several subsets of T cells. -Actions of T cells are dictated by the APCs that activate them. -Restricted: require some type of MHC (self) recognition before they can be activated -All T cells produce cytokines with a spectrum of biological effects. -End result of T-cell stimulation is the mobilization of other T cells, B cells, and phagocytes.

Clonal Selection and Expansion

•Clonal selection: - The mechanism by which the exactly correct B or T cell is activated by any incoming antigen (selecting for the right fit) -Lymphocyte specificity is preprogrammed, existing in the genetic makeup before an antigen has ever entered the tissues. -Each genetically distinct lymphocyte expresses only a single specificity and can react to only one type of antigen. •Clonal expansion: the rapid multiplication of B or T cell clones after activation by an antigen (increase the number of cells with the right fit).

Host rejection of graft

•Cytotoxic T cells of a host recognize foreign class I MHC markers. •Release IL-2 as part of general immune mobilization •Helper and cytotoxic T cells bind to the grafted tissue and secrete lymphokines that begin the rejection process within 2 weeks of transplantation. •Antibodies are formed against the transplanted tissue and contribute to damage. •The result is destruction of the vascular supply and death of the graft.

Allergy "Vaccines"

•Desensitization or hyposensitization: -Therapeutic way to prevent reactions between allergen, IgE, and mast cells -Allergen preparations include pure, preserved suspensions of plant antigens, venoms, dust mites, dander, and molds. -Blocking antibodies: one hypothesis is that injected allergens stimulate formation of these allergen-specific IgG antibodies -Also hypothesized that allergen delivered in this fashion combines with IgE itself, taking it out of circulation

Drug Allergy

•Drugs are foreign compounds capable of stimulating allergic reactions. •Drug allergy is one of the most common side effects of treatment, affecting 5 - 10% of hospitalized patients. •Reactions range from a mild rash to fatal anaphylaxis. •Compounds implicated: -Antibiotics: penicillin -Synthetic antimicrobials: sulfa drugs -Aspirin -Opiates -Contrast dye used in X rays •Allergen is not the intact drug itself, but a hapten given off when the liver processes the drug.

Primary Immunodeficiency Diseases

•Due to an inherited abnormality •In some diseases, the lymphocytes are absent, or present at low levels. •In other diseases, the lymphocytes are present, but do not function normally. •An individual can lack either B or T cells, or both other cells. •Genetic deficiencies in B-cell development or expression can also be responsible. •Agammaglobulinemia - absence of gamma globulin •Lack of antibodies can be contributed to this condition. •IgA deficiency is the most prevalent form •Absence of or dysfunction of T-cell is or can be more devastating than B-cell dysfunction. Eg abnormal development of the thymus - DiGeorge syndrome.

Who Is Affected (cont'd)

•Generalized susceptibility to allergens is inherited, not the allergy to a specific substance. •Genetic basis for atopy: -Increased IgE production -Increased reactivity of mast cells -Increased susceptibility of target tissue to allergic mediators •The prospect of a child's developing atopic allergy is 25% if parents are afflicted and 50% if siblings or grandparents are afflicted. •Hygiene hypothesis: •Effect of breastfeeding: •Human Microbiome Project:

Effects of Molecular Size and Shape (cont'd)

•Haptens -Small foreign molecules that are too small by themselves to elicit an immune response -If this incomplete molecule is linked to a larger carrier molecule, the combination develops immunogenicity. -The hapten serves as the epitope.

IgE- and Mast-Cell-Mediated Allergic Conditions: Atopic Diseases

•Hay fever: -A generic term for allergic rhinitis •Asthma: -Respiratory disease characterized by episodes of impaired breathing due to severe bronchoconstriction •Atopic dermatitis/eczema: -Intensely itchy inflammatory condition of the skin -Sensitization occurs through ingestion, inhalation, and skin contact with allergens. -Usually begins in infancy and is characterized by reddened, weeping, encrusted skin lesions on the face, scalp, neck, and inner surfaces of limbs and trunk. -Progresses to a dry, scaly, thickened skin condition in adults -Lesions are itchy, painful, and predisposed to secondary bacterial infections.

Cytokines, Target Organs, and Allergic Symptoms

•Histamine: -Constricts smooth muscle, Relaxes vascular smooth muscle -Stimulates eosinophils to release inflammatory cytokines, escalating symptoms •Bradykinin: -Prolonged smooth muscle contraction of the bronchioles, Dilation of peripheral arterioles -Increased capillary permeability, Increased mucus secretion •Serotonin: effects appear to complement those of histamine and bradykinin •Leukotriene: -"Slow-reacting substance of anaphylaxis" -Induces gradual contraction of smooth muscle, Vascular permeability, Mucus secretion, Stimulates polymorphonuclear leukocytes

The Specific B-Cell Receptor: An Immunoglobulin Molecule

•Immunoglobulin (Ig): -Large glycoprotein molecules that serve as the antigen receptors of B cells -When secreted are antibodies •Immunoglobulin structure: -Antigen binding sites: pockets in the ends of the forks of the molecules that can be highly variable in shape to fit a wide range of antigens -Variable regions: areas of extreme versatility from one clone to another -Light chains, heavy chains, constant regions: amino content does not vary greatly from one antibody to another

The Immune Response (cont'd)

•Immunopathology: the study of disease associated with the overreactivity or underactivity of the immune response •Hypersensitivity: -Allergy and autoimmunity -Tissues are attacked by immunologic functions that can't distinguish between self and nonself. •Hyposensitivity or immunodeficiency: immune system is incompletely developed, suppressed, or destroyed

Antigen processing and presentation

•In most immune reactions, the antigen must be further acted upon and formally presented to lymphocytes by antigen presenting cells (APCs). •Examples of APCs: -Macrophages -B cells -Dendritic cells After processing is complete, the antigen will be bound to the MHC receptor and moved to the surface of the APC so it will be readily accessible to T lymphocytes

The Nature of Allergens and Their Portals of Entry (cont'd)

•Inhalants: airborne environmental allergens such as pollen, house dust, dander, or fungal spores •Ingestants: allergens that enter by mouth that cause food allergies •Injectant: allergies triggered by drugs, vaccines, or hymenopteran (bee) venom •Contactants: -Allergies that enter through the skin -Many are type IV (delayed) hypersensitivities

Type IV Hypersensitivities: Cell-Mediated (Delayed) Reactions

•Involves primarily the T-cell branch of the immune system. •Results when T cells respond to antigens displayed on self tissues or transplanted foreign cells •Traditionally known as "delayed hypersensitivity": -Symptoms arise one to several days following the second contact with antigen.

Type III Hypersensitivities:Immune Complex Reactions

•Involves the reaction of soluble antigen with antibody, and deposition of resulting complexes in various tissues in the body: -Involves the production of IgG and IgM antibodies -Also involves the activation of complement -Unlike type II hypersensitivities, antigens are not attached to the surface of a cell. -Immune complex reaction: produces free floating complexes that are deposited into tissues

Mechanisms of Immune Complex Disease

•Large quantities of antibodies are produced in response to an exposure to a profuse amount of antigen. •Upon second exposure, antigen-antibody complexes are formed. These recruit complement and neutrophils that would normally eliminate these complexes. •In immune complex disease, these complexes are deposited in the basement membrane of epithelial tissues: -Neutrophils release lysosomal granules that digest tissues and cause a destructive inflammatory condition.

Antigen Processing and Presentation (cont'd)

•Most antigens must be presented first to T cells, even though they will eventually activate both the T-cell and B-cell systems. •T-cell-independent antigens: antigens that can trigger B cells directly without APCs or T helper cells -Carbohydrates with many repeating and invariable determinant groups

Food Allergy

•Most common food allergens come from peanuts, fish, cow's milk, eggs, shellfish, and soybeans. •Mode of entry is intestinal. •Symptoms include vomiting, diarrhea, and abdominal pain. •Other manifestations include hives, rhinitis, asthma, and occasionally anaphylaxis. •Hypersensitivity involves IgE and degranulation of mast cells, but not all reactions involve this mechanism. •Care should be taken vaccinating individuals with egg allergies.

Serum Sickness

•Named for a condition in soldiers treated with horse serum for tetanus: -Also caused by injections of animal hormones and drugs •A systemic injury initiated by antigen-antibody complexes that circulate in the blood and settle into membranes at various sites: -Kidney, heart, skin, and joints -Condition can become chronic causing enlarged lymph nodes, rashes, painful joints, swelling, fever, and renal dysfunction.

Immunodeficiency Diseases:Hyposensitivity of the Immune System

•Occasionally, an individual is born with or develops weakened immune responses. •Predominant consequences of immunodeficiencies are recurrent, overwhelming infections with opportunistic microbes. •Primary immunodeficiencies: present at birth (congenital), usually stemming from genetic errors •Secondary immunodeficiencies: acquired after birth and caused by natural or artificial agents

Hemolytic Disease of the Newborn and Rh Incompatibility

•Placental sensitization occurs when the mother is Rh- and the unborn child is Rh+: -Fetal RBCs may leak into the mother's circulation during childbirth when the placenta detaches. -Mother's immune system detects the foreign Rh factors on fetal RBCs and is sensitized to them by producing antibodies and memory B cells. •In the next pregnancy with an Rh+ fetus: -Fetal blood cells escape into maternal circulation late in pregnancy, eliciting a memory response. -Maternal anti-Rh antibodies cross the placenta, affix to fetal RBCs, and cause complement-mediated lysis. •Potentially fatal hemolytic disease of the newborn (HDN): -Also called erythroblastosis fetalis -Characterized by severe anemia and jaundice -Treated with shots of RhoGAM

Cytokines, Target Organs, and Allergic Symptoms (cont'd)

•Prostaglandins: -Regulate smooth muscle contraction; stimulate uterine contractions during delivery -Vasodilation -Increased vascular permeability -Increased sensitivity to pain -Bronchoconstriction -Nonsteroidal anti-inflammatory drugs (NSAIDs) prevent the actions of prostaglandins.

Diagnosis of Allergy:In Vivo Methods

•Skin Testing: In vivo method to detect precise atopic or anaphylactic sensitivities -Skin is injected, scratched, or pricked with a small amount of pure allergen extract. -20 minutes after antigenic challenge, a wheal and flare result shows sensitivity. -The diameter of the wheal is measured and rated on a scale from 0 (no reaction) to 4 (greater than 15 mm).

Graft Rejection of Host

•Some grafted tissues (bone marrow) contain indigenous populations of passenger lymphocytes. •These lymphocytes create an immune response to the host . •Graft versus host disease: -Graft attacks any host tissue bearing MHC markers. -Effects are systemic and toxic.

Stage I: The Development of Lymphocyte Diversity

•Specific events in T-Cell Maturation -Maturation of T cells and development of their receptors is directed by the thymus gland and its hormones. •CD3 receptors: surround the T-cell receptor and assist in binding •CD4 receptors: accessory receptor proteins that binds to MHC II molecules •CD8 receptors: found on cytotoxic T cells and binds to MHC I molecules

T Helper (TH) Cells

•Three types of T helper cells that all bear the CD4 marker and are critical in regulating immune reactions to antigens •Also involved in activating macrophages -Directly by receptor contact -Indirectly by releasing cytokines such as interferon gamma (IFNγ) •Secrete interleukin 2 (IL-2), which stimulates primary growth of T cells, including cytotoxic T cells •Secrete IL-4, IL-5, and IL-6, which stimulate B cells •Make up about 65% of the T-cell population

Types of Transplants

•Transplantation has been performed on every major organ, but most often involves the skin, liver, heart, kidney, coronary artery, cornea, and bone marrow. •Sources of organs: -Live donors: kidney, skin, bone marrow, and liver -Cadavers: heart, kidney, and cornea -Fetal tissue: stem cells

T Cells and Their Role in Organ Transplantation

•Transplantation or grafting of organs is a common medical procedure. •Although it is life-giving, it is plagued with the natural tendency of lymphocytes to seek out and destroy foreign antigens. •The bulk of the damage that occurs in graft rejections are attributed to cytotoxic T-cell action.

Hypersensitivity: Four Types

•Type I: anaphylaxis, allergies such as hay fever, asthma - Rapid •Type II: blood group incompatibility, pernicious anemia, myasthenia gravis •Type III: systemic lupus erythematosus, rheumatoid arthritis, serum sickness, rheumatic fever •Type IV: Infection reactions, contact dermatitis, graft rejection

How B Cells Respond to Antigen: Release of Antibodies

•When activated, B cells divide and give rise to plasma cells. •Plasma cells release antibodies into the tissue and the blood. •Antibodies attach to the antigen for which they are specific, and the antigen is marked for destruction or neutralization.

B and T cells constantly recirculate through the

•circulatory system and lymphatics, migrating into and out of the lymphoid organs.