Immunity

The ability to defend against infectious agents, foreign cells, and cancer cells

Immune System Antigen—any molecule that the body recognizes as nonself and that provokes an immune response. Three lines of defense Protective barriers Innate immunity Adaptive immunity

Protective Barriers Intact skin—prevents entry Ciliated mucous membranes—trap & sweep out foreign particles Oil & other exocrine glands—secrete bacterial inhibitors Low pH in digestive & urinary tract—kill invading bacteria Normal microbes of skin, GI tract, genitals—keep foreign bacteria in check

Non-Specific Defenses Complement proteins Coat invading pathogens Some form pores that cause pathogen to lyse Some promote inflammation Some attract phagocytic cells

Non-Specific Defenses Macrophages Non-specific & specific Ingest dust and debris (especially in lungs) Ingest microbes

Non-Specific Defenses Inflammatory Response Invader penetrates Injured cells produce chemicals Cytokines & histamines Capillaries dilate WBCs penetrate more easily Opsonization—invader coated in complement Chemotaxis—WBCs attracted to site due to alarm chemicals WBCs form macrophages Macrophages ingest & digest

Non-Specific Defenses Inflammatory Response (cont.) Redness & warmth— blood rushing to site Swelling—tissue fluids increasing, large numbers of macrophages Pain—increased fluid pressing on nociceptors

Non-Specific Defenses Fever Macrophages release signals to hypothalamus Mild fever increases enzyme activity & metabolism Formation & action of phagocytes increases Tissue repair increases Many microbes grow slowly at higher temperatures

Specific Defenses Relies on detecting antigens B & T lymphocytes One of types of WBCs Central to adaptive immunity Antibody-mediated immunity Cell-mediated immunity

Antibody-Mediated Immunity Also called “humoral” immunity B lymphocytes produced in bone marrow Each B cell is antigen-specific Antigen receptors on surface (determined gentically) Will only respond to specific antigen

Antibody-Mediated Immunity B cell matches to antigen Engulfs, digests antigen Displays antigen fragments Helper T cell attracted T cell releases cytokines B cell stimulated to multiply & change into plasma cells Plasma cells produce antibodies

Antibody-Mediated Immunity Once infection is over, most B cells die Some retained as memory B cells On future infections, can respond faster

Antibody-Mediated Immunity Antibodies produced by plasma cells Antibody Structure Light chain Heavy chain Antigen binding site

Antibody-Mediated Immunty Antibody Types (Immunoglobulin) IgG Most numerous & diverse (75-85%) Bacteria, viruses, toxins Crosses placenta IgM First secreted Stimulates complement cascade IgD Activates & matures B cells IgA Saliva, sweat, milk, etc. Prevents pathogens from attaching to epithelium IgE Binds to basophils Release histamines during inflammation & allergic reactions

Antibody-Mediated Immunity Antibody Functions (PLAN) Precipitation Form large complexes with molecules Complexes settle in solution Easier to phagocytize Lysis Enhances complement action of making holes in cells Agglutination Form large complexes with cells Complexes clump Easier to phagocytize Neutralization Block binding sites used to invade tissue cells

Cell-Mediated Immunity T lymphocytes Produced in bone marrow Mature in thymus gland Cannot recognize antigens Antigen-presenting cell (APC) Macrophages, dendritic cells Engulf antigen Complex formed on cell surface Binds to T cell, activating it

Cell-Mediated Immunity T cell encounters APC T cell activated T cell multiplies, specializes Can attack pathogens directly Can attack cells invaded by pathogens

Cell-Mediated Immunity Cytotoxic T cells Kill infected cells by perforating cell membrane Primary defense against infected cells, tumors Cause rejection of tissue & organ transplants Helper T cells Stimulate B & T cell maturity Enhance macrophage activity Memory T cells Like memory B cells, remain after infection Suppressor T cells Slow & stop immune response after infection over

Types of Immunity Natural Active production—exposed to pathogen Passive production—through placenta or milk Artificial Active production—vaccination with dead or altered pathogen Passive production—direct injection of antibodies or anti-serum

Immune Disorders Immunodeficiency Weak immune system Usually due to low WBC count Cancer, HIV, chemotherapy, radiation Autoimmune disease Body recognizes cell proteins as “non-self” antigens Lupus, rheumatoid arthritis, multiple sclerosis Hypersensitivity Immune response unusually strong Acute—minutes (anaphylaxis) Subacute—minutes to hours (blood transfusion) Delayed—hours to days (poison ivy)