chapter 15 - adaptive immunity

adaptive immunity

• specific

• inducible

• has memory

goal of adaptive immunity

recognize and eliminate specific pathogens while remembering them for faster future responses

key traits of adaptive immunity

• Antigen specificity – targets specific epitopes.

• Inducible – activated upon exposure.

• Memory – stronger secondary response.

• Tolerance – avoids attacking “self.”

immune tolerance

prevents immune system from damaging self-tissues

central tolerance

eliminates self-reactive lymphocytes (T in thymus, B in bone marrow)

peripheral tolerance

controls mature cells that escape central tolerance

cell types of lymphocytes

• B cells

• T cells

maturation site of B cells

Bone marrow

maturation site of T cells

Thymus

Main function of B cells

humoral response (antibodies)

Main function of T cells

cell-mediated response

adaptive immunity divisions

• Humoral (B cells) → antibodies defend against extracellular pathogens.

• Cell-mediated (T cells) → kills infected or abnormal cells.

lymphatic system

• Returns fluids to blood circulation.

• Screens for foreign antigens via lymph nodes and secondary lymphoid organs.

anitgen

molecule recognized by immune system

epitope

specific 3D region that antibodies or receptors bind to

Each B or T cell recognizes only ___

one unique epitope

antibody functions

• neutralization

• opsonization

• complement activation (fixation)

• agglutination

• ADCC (Antibody-dependent cellular cytotoxicity)

BCR (B-cell receptor) recognizes ___

one specific antigen

when a BCR is activated, ___

it becomes a plasma cell that secretes antibodies

antibody =

immunoglobulin (Ig)

neutralization

block pathogen/toxin attachment

opsonization

coat pathogen for easier phagocytosis

complement activation (fixation)

trigger complement cascade

aggglutination

clump microbes together

ADCC (antibody-dependent cellular cytotoxicity)

antibodies tag cells for NK cell destruction

antibody classes

• IgM

• IgG

• IgA

• IgE

• IgD

major features of IgM

• 1st produced

pentamer

major features of IgG

• most abundant

• crosses placenta

major features of IgA

in mucosal secretions (tears, saliva, milk)

major features of IgE

allergies and parasites

major features of IgD

• low levels

• unclear function

functions of IgM

• complement activation

• agglutination

functions of IgG

• neutralization

• opsonization

• complement

• ADCC

functions of IgA

• mucosal defense

• neutralization

functions of IgE

binds to mast cells/basophils —> histamine release

functions of IgD

B-cell receptor role

TCR (T-cell receptors) recognizes ___

antigen only when presented on MHC

only one TCR type per cell, but ___

many copies on surface

CD markers

• CD4+

• CD8+

CD4+ (helper T cells)

recognizes MHC II (on APCs)

CD8+ (cytotoxic T cells)

recognize MHC I (on all nucleated cells)

MHC I are found on

all nucleated cells

MHC II are found on

APCs (B cells, macrophages, dendritic cells)

MHC I presents to

CD8+ Tc cells

MHC II presents to 

CD4+ Th cells

function of MHC I

displays intracellular antigens (virus-infected or abnormal cells)

function of MHC II

displays extracellular antigens

Types of T cells

• cytotoxic T (Tc)

• Helper T (Th)

• Regulatory T (Treg)

cytotoxic T (Tc)

kill infected cells via perforin/granzyme or trigger apoptosis

Helper T (Th)

Activate B cell, macrophages, and Tc cells via cytokines

Regulatory T (Treg)

suppress excessive immune reactions

Natural killer (NK) cells

• Bridge innate and adaptive immunity.

• Kill virus-infected or cancer cells that lack MHC I.

• Perform ADCC when antibodies coat the target.

immune response stages

1. antigen recognition

2. activation

3. clonal expansion

4. differentiation

5. memory response

antigen recognition stage

BCR or TCR binds specific epitope

activation stage

co-stimulation and cytokine signaling

clonal expansion stage

multiplication of activated lymphocytes

differentiation stage

into effector (attack) and memory cells

memory response stage

faster, stronger secondary response upon re-exposure