Chapter 43: The Immune System

Lymphocytes: Specialized White Blood Cells : Two Types: B Lymphocytes T Lymphocytes

Lymphocytes: B cells: Formed and mature in red bone marrow Named for Bursa of Fabrica (birds) T Cells Formed in red bone marrow Mature in Thymus

Lymphocyte Action: Primary lymphatic organs: Red bone marrow Thymus Secondary lymphatic organs: Lymph tissue, nodule and nodes SpleenTonsils Interacts with APC, antigens and other lymphocytes

Lymphocyte Activation: 1. Antigen recognition Epitope- antigenic determination Specific sites on the antigen that is recognized by lymphocyte Many different determinants on each antigen 2. Proliferation and destruction

Antigen Receptors: B cell receptors Y shape 2 heavy chains 2 light chains Disulfide linkages Anchored to cell Variable region acts as specific antigen binding site T cell receptors Two chains α- chain β- chain Disulfide linkages Anchored to cell Variable region acts as specific antigen binding site

Major Histocompatibility Complex: MHC MHC complexes present antigen particles to the surface of the host cell Necessary for immune response

Two Types Of MHC: MHC I Found on all nucleated cells Will display to cytotoxic T cells MHC II Found on all APC’s, including: B- cells Macrophages Dendritic cells Will display to helper T cells

Cytotoxic T cells: Cell Mediated Immune Response Cell Mediated Immune Response Viruses, Cancer and other intracellular pathogens Viruses, Cancer and other intracellular pathogens Associated with MHC I Associated with MHC I CD8 surface protein CD8 surface protein Enhances interaction between cytotoxic T cell and APC Enhances interaction between cytotoxic T cell and APC Activation is stimulated by cytokines from helper T cells Activation is stimulated by cytokines from helper T cells

Cytotoxic T Cells: Once Activated cytotoxic T cells release: Perforins- create pores in the cell membrane of the host cell Use proteolytic enzymes to initiate apoptosis

Helper T Cells: Cell Mediated and Humoral Immune Response Activated by: APC Cytokine released by macrophage Associated MHC II CD4 surface proteins-enhance interaction between helper T cell and APC Releases cytokines: Interferonsinterleukins

Cytokine Action: Interferons: Prevent viral replication Activates macrophages and NK cells Secreted by virus infected cells, fibroblasts, macrophages and B cells Interleukins: Costimulation of T and B cells Prostaglandin production Inflammatory response Activates macrophages and NK cells Produces eosinophils Secreted by B cells, macrophages and fibroblasts

Clonal Selection: Antigen binding to receptor Lymphocyte proliferation forming clones of identical cells Cells bearing same receptors Differentiation: Effector cells- fight off primary infection Memory cells- rapid response upon secondary exposure of same antigen

Induction of Immune Response Primary immune response Selective proliferation and differentiation of lymphocytes from first exposure day peak response time Secondary immune response Fast response time to secondary exposure of same antigen 2-7 days peak response time.

Types of Immune Response: Humoral Immunity B cell activation Production of antibodies Defense against bacteria free in the lymph and blood plasma, incompatible tissues, pollen and bee venom (extracellular pathogens) Cell- Mediated Immunity T cell activation Binds to and/or lyses cells Defend against intracellular pathogens, including; viruses, bacteria, fungi, protozoa, parasites and cancer cells

Antibody Structure and Function: Epitope: region on antigen surface recognized by antibodies 2 heavy chains and 2 light chains joined by disulfide bridges Antigen-binding site (variable region)

Structure of an antibody:

5 classes of Immunoglobins IgM: 1st to circulate; indicates infection; too large to cross placenta IgG: most abundant; crosses walls of blood vessels and placenta; protects against bacteria, viruses, & toxins; activates complement IgA: produced by cells in mucous membranes; prevent attachment of viruses/bacteria to epithelial surfaces; also found in saliva, tears, and perspiration IgD: do not activate complement and cannot cross placenta; found on surfaces of B cells; probably help differentiation of B cells into plasma and memory cells IgE: very large; small quantity; releases histamines-allergic reaction

Antibody- mediated Antigen Disposal: Opsonization: antibody binds to and blocks antigen activity-coats antigen surface enhancing macrophage activity Agglutination: antigen clumping- antibodies contain at least two antigen binding sites Precipitation: cross-linking of soluble antigens- forms immobile aggregates that are disposed of by phagocytosis Viral Neutralization: antibodies bind to certain proteins on the surface of a virus blocking its ability to infect a host cell

Immunity in Health & Disease Active immunity Depends on persons own lymphocytes natural: conferred immunity by recovering from disease artificial: immunization and vaccination; produces a primary response Passive immunity transfer of immunity from one individual to another transfer of immunity from one individual to another natural: mother to fetus; breast milk artificial: rabies Transfer of antibodies from rabid(immune) animal to non-rabid (non- immune) animal

Blood Groups: Why is blood type AB the universal recipient and blood type O the universal donar?

Tissue and Organ Transplant MHC’s responsible for rejection of tissue and organ transplant No two individuals have exact same MHC’s Exceptions??? How do doctors compensate for this???

Abnormal Immune Function: Allergies (anaphylactic shock): hypersensitive responses to environmental antigens (allergens); causes dilation and blood vessel permeability Allergy symptoms can be diminished with antihistamines The hormone epinephrine counter acts this allergic reaction

Self/Nonself Recognition: Self-tolerance: capacity to distinguish self from non-self Autoimmune diseases: failure of self- tolerance; multiple sclerosis, lupus, rheumatoid arthritis, insulin-dependent diabetes mellitus

Immune Deficiencies: Inborn (primary): defects in the development of various immune system cells and or proteins defects in the development of various immune system cells and or proteins SCID- severe combined immunodeficiency SCID- severe combined immunodeficiency No cell-mediated immune response Requires bone marrow transplant

Acquired (secondary) AIDS: Acquired Immunodeficiency Syndrome HIV virus (Human Immunodeficiency Virus) Retrovirus Uses CD4 receptor to enter cell Causes loss of helper T cells