Chapter 39Immunity

ImmunityThe ability to defend against infectious

agents, foreign cells, and cancer cells

Immune SystemAntigen—any molecule

that the body recognizes as nonself and that provokes an immune response.

Three lines of defenseProtective barriersInnate immunityAdaptive immunity

Protective BarriersIntact skin—prevents entryCiliated mucous membranes—trap & sweep

out foreign particlesOil & other exocrine glands—secrete

bacterial inhibitorsLow pH in digestive & urinary tract—kill

invading bacteriaNormal microbes of skin, GI tract, genitals—

keep foreign bacteria in check

Non-Specific DefensesComplement

20-30 proteinsCoat invading pathogensSome form pores that cause

pathogen to lyseSome promote inflammationSome attract phagocytic cells

Non-Specific DefensesMacrophages

Non-specific & specificIngest dust and debris (especially in lungs)Ingest microbes

Non-Specific DefensesInflammatory Response

Invader penetratesInjured 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 macrophagesMacrophages ingest &

digest

Non-Specific DefensesInflammatory

Response (cont.)Redness & warmth—

blood rushing to siteSwelling—tissue

fluids increasing, large numbers of macrophages

Pain—increased fluid pressing on nociceptors

Non-Specific DefensesFever

Macrophages release signals to hypothalamusMild fever increases enzyme activity &

metabolism Formation & action of phagocytes increases Tissue repair increases

Many microbes grow slowly at higher temperatures

Specific DefensesRelies on detecting antigensB & T lymphocytes

One of types of WBCsCentral to adaptive immunity

Antibody-mediated immunityCell-mediated immunity

Antibody-Mediated ImmunityAlso called “humoral” immunityB lymphocytes produced in bone marrowEach B cell is antigen-specific

Antigen receptors on surface (determined gentically)

Will only respond to specific antigen

Antibody-Mediated ImmunityB cell matches to antigenEngulfs, digests antigenDisplays antigen fragmentsHelper T cell attractedT cell releases cytokinesB cell stimulated to multiply &

change into plasma cellsPlasma cells produce

antibodies

Antibody-Mediated ImmunityOnce infection is over,

most B cells dieSome retained as

memory B cellsOn future infections, can

respond faster

Antibody-Mediated ImmunityAntibodies produced by plasma cellsAntibody Structure

Light chainHeavy chainAntigen binding site

Antibody-Mediated ImmuntyAntibody Types

(Immunoglobulin)IgG

Most numerous & diverse (75-85%)

Bacteria, viruses, toxins

Crosses placentaIgM

First secreted Stimulates

complement cascade

IgD Activates & matures B

cellsIgA

Saliva, sweat, milk, etc. Prevents pathogens

from attaching to epithelium

IgE Binds to basophils Release histamines

during inflammation & allergic reactions

Antibody-Mediated ImmunityAntibody Functions (PLAN)

Precipitation Form large complexes with molecules Complexes settle in solution Easier to phagocytize

Lysis Enhances complement action of

making holes in cellsAgglutination

Form large complexes with cells Complexes clump Easier to phagocytize

Neutralization Block binding sites used to invade

tissue cells

Cell-Mediated ImmunityT lymphocytes

Produced in bone marrowMature in thymus glandCannot recognize antigens

Antigen-presenting cell (APC)Macrophages, dendritic cellsEngulf antigenComplex formed on cell surfaceBinds to T cell, activating it

Cell-Mediated ImmunityT cell encounters APCT cell activatedT cell multiplies, specializesCan attack pathogens directlyCan attack cells invaded by

pathogens

Cell-Mediated ImmunityCytotoxic T cells

Kill infected cells by perforating cell membranePrimary defense against infected cells, tumorsCause rejection of tissue & organ transplants

Helper T cellsStimulate B & T cell maturityEnhance macrophage activity

Memory T cellsLike memory B cells, remain after infection

Suppressor T cellsSlow & stop immune response after infection over

Types of ImmunityNatural

Active production—exposed to pathogen

Passive production—through placenta or milk

ArtificialActive production—

vaccination with dead or altered pathogen

Passive production—direct injection of antibodies or anti-serum

Immune DisordersImmunodeficiency

Weak immune systemUsually due to low WBC countCancer, HIV, chemotherapy, radiation

Autoimmune diseaseBody recognizes cell proteins as “non-self” antigensLupus, rheumatoid arthritis, multiple sclerosis

HypersensitivityImmune response unusually strongAcute—minutes (anaphylaxis)Subacute—minutes to hours (blood transfusion)Delayed—hours to days (poison ivy)