BIO3 - Chapter 17

Adaptive Immunity: Specific Defenses of the Host

is vaccination innate or adaptive immunity

adaptive

how many systems of adaptive immunity are there

2, humoral and cellular

humoral immunity

aka antibody-mediated immunity, is directed at freely circularing pathogens & depends on B cells

cellular immunity

aka cell-mediated immunity, depends on T cells to eliminate intracellular pathogen, reject foreign tissue recognizes as nonself, & destroy tumor cells

T & B cell development

develop from stem cells in red bone

where to B cells mature

bone marrow

what do B cells do

recognize antigens & make specific antibodies against them, recognition depends on receptors to the antigens that coat the surface of the B cell

where do T cells mature

thymus

significance of T cell receptors (TCRs)

contact antigens, causing the T cells to secrete cytokines instead of antibodies

what does celllular immunity attack

antigens that have already entered cells; viruses & some intracellular bacteria

what does humoral immunity fight

invaders & threats outside cells; extracellular bacteria & toxins, viruses before they enter a host cell

what is an antigen (Ag)

a substance that causes the body to produce specific antibodies or sensitized T cells; anything that doesn’t belong to the body

characteristsics of an Ag

often components of invading microbes, or nonmicrobial antigens (pollen, egg white, etc.), are proteins or large polysaccharides

antigen molecular weight

10,000 or higher

hapten

low molecular weight antigen, combines w carrier molecules to stimulate an immune response

antibodies

globular proteins called immunoglobins (Ig), soluble

significance of antigen-binding sites

most human antibodies have 2 binding sites - called bivalence

antibody structure

2 identical light chains

2 idenitcal heavy chains

S-S links

Y shaped molecule

V - variable regions

C - constant regions

Y-shaped monomers

IgG, IgD, IgE

aggregates of 2 or 3 monomers

IgA & IgM

IgG antibodies significance

monomer

80% of serum Abs

in blood, lymph, & intestine

cross placenta

enhance phagocytosis, trigger the complememt system, neutralize toxins & viruses; protects fetus & newbown

half-life = 23 days

what is half-life

time it takes for half the pop to disappear

IgM antibodies significance

pentamer (macro)

6% of serum Abs

active complement system

in blood, lymph, & on B cells

agglutinates microbes, cause clumping of cells & viruses; first response to an infection; short lives

half-life = 5 days

IgA antibodies significance

monomer in serum, dimer in secretions

13% of serum Abs

common in mucous membranes, saliva, tears & body secretions

prevent microbial attachment to mucous membrane; important in resistance to intestinal & respiratory pathogens

half-life = 6 days

IgD antibodies significance

monomer

0.02% of serum Abs

structure similar to IgG

in blood, lymph, & on B cells

no well-defined function; assists in the immune system response on B cells

half-life = 3 days

IgE antibodies significance

monomer

0.002% of serum Abs

on mast cells, basophils, & in blood

cause the release of histamines when bound to antigen; respond to allergic reaction, lysis of parasitic worms

half-life = 2 days

significance on inactive B cells

contain surface immunoglobulins that bind to antigen. most are IgM & IgD

why do B cells need to be activated

to prod plasma cells that make antibodies & memory cells

activation of B cell

B cell’s Ig bind to the epitope for which they become specific, the B cell is activated (T-independent antigen)

T-dependent antigens

B cells that require assistance of a T helper cell

significance of major histocompatibility complex (MHC)

genes that encode molecules on the cell surface

class I MHC

on the membrane of the nucleated animal cells, identify “self”

class II MHC

on the surface on antigen-presenting cells (APCs), including B cells

T-dependent antigens

Ag presented w MHC to T helper cell (T_H)

T_H cell produces cytokines that activate the B cell

what happens after activation of B cells

clonal selection & expansion

what does clonal selection do

differentiates activated B cells into antibody-producing plasma cells and memory cells

what does clonal deletion do

eliminated harmful B cells

T-dependent antigen

antigen that requires a T_H cell to produce antibodies

T-independent antigens

stimulate the B cell without the help of T cells

tend to be molecules consisting of repeard subunits (like capsules)

provoke a weak immune response, usually producing IgM

no memory cells generated

how to antigen-antibody complex form

when antibodies bind to antigens

affinity

strength of the bond

significance of the antigen-antibody complex

protects the host by tagging foreign molecules or cells for destruction, results in:

agglutination

opsonization

antibody-dependent cell-mediated cytotoxicity

neutralization

activation of the complement system

agglutination

clumps bacteria

opsonizatioin

enhances phagocytosis

neutralization

antibody grabs toxin & blocks attachement

complement fixation (complement activation)

triggers complement system & leads to lysis

significance of thymic selection

eliminates immature T cells

different kinds of T cells

T helper cells

T cytotoxic cells

T regulatory cells

how do T cells respond to antigen

by T-cell receptors

what does the recognition of antigen by a T cell require

antigen-presenting cells (APCs)

how might T cells be classified

by certain glycoprotein on their surface called clusters of differentiation (CD)

significance of CD4+ or T_H cells

T-helper cells, TCRs recognize antigens & MHC II on APC

What do T_H cells do after activation

produce cytokines & differentiate into T_H1, T_H2, or memory cells

what does T_H1 do

produce IFN-Y, which activates cells related to cell-mediated immunity, macrophages, & antibodies

what does T_H2 do

activate eosinophils & B cells to produce IgE

what are the T cytotoxic cells

CD8+ or T_C cells

what do T cytotoxic cells do

target altered host cells, such as tumor cells, transplanted foreign tissue, & viral/parasite infected cells (which carry engogenous antigens)

what are T cytotoxic cells activated into

cytotoxic T lymphocytes (CTLs)

what do cytotoxic T lymphoctes (CTLs) do

recognize antigens + MHC I

nduce apoptosis in target cells

release perforin & granzymes

what do T regulatory cells do

suppress T cells against self, avoid reacting against the body’s self

suppress immature T cells that escape deletion in the thymus

rotect the intestical bacteria from immune system & other useful function

play a role in protecting the fetus from rejection as non self

T regularoty cell surface

CD4 & CD25 on surface

what do antigen-presenting cells do

digest antigen

what are cytokines

chemical messengers produced by all cells of the immune system in response to a stimulus. communicators between leukocytes - interleukins

cytokine storm

overproduction of cytokines, causes significant damage to tissues

antibody tites

the amount of antibody in serum - reflects intensity of the humoral response

primary response

occurs after initial contact with antigen

secondary (memory or anamnestic) response

occurs after second exposure

naturally acquired active immunity

results from infection

naturally acquired passive immunity

transplacental or via colostrum

artificially acquired active immunity

injection of Ag (vaccination)

artificially acquired passive immunity

injection of Ab