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Immunity
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
 20-30 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)