micro human pathogens module 3 SG

what are the two main features of adaptive immunity

specificity and memory

what are the two major arms of adaptive immunity

humoral and cell mediated

what mediates humoral immunity

b cells and antibodies

what mediates cell mediated immunity

t cells

what happens during the first exposure to an antigen

the adaptive response takes days to develop

what happens during later exposure to the same antigen

the response is faster and stronger

what do activated b cells become

plasma cells or memory b cells

what do plasma cells do

produce antibodies

what is the b cell receptor

membrane-bound immunoglobulin

where do t cells originate

bone marrow

where do t cells mature

thymus

what receptor do t cells use

TCR- t cell receptor

what is the main job of CD8+ T cells

kill infected or cancerous host

what is the main job of CD4+ T cells

suppress immune responses and maintain tolerance

what is an antigen

a substance capable of provoking an immune response

what is an epitope

the specific region of an antigen recognized by an immune receptor

continuous vs discontinuous epitope

continuous=linear sequence

discontinuous=depends on 3d folding

immunogenity

ability of a substance to induce an immune response

what factors influence immunogenity

foreignness, size, complexity, genetics, dose, route, timing

hapten

small weak immunogen that needs a carrier to become strongly immunogenic

what does the Fab region of an antibody do

binds antigen

what does the Fc region of an antibody do

interacts with immune cells and complement

major antibody functions

opsonization, neutralization, agglutination, complement, ADCC

what does t dependent b cell activation require

helper t cell assistance

does t dependent activation produce memory cells

yes

does t independent activation produce memory cells

no

what usually triggers t independent b cell activation

repetitive antigens like capsules, polysaccharides, LPS

why are t independent antigens important in children under 2

children under 2 respond poorly to them

what is the basic t dependent activation sequence

BCR binds antigen… MHC II presentation… helper t cell co-simulation

what is the key co-stimulatory interaction in t dependent b cell activation

CD40 on b cell and CD40L on helper t cell

what does VDJ recombination do

created BCR diversity during b cell development

what does somatic hypermutation do

produces higher affinity antibodies after activation

which antibody is produced first in a primary response

IgM

what is IgM’s structure

pentamer

which antibody dominates the secondary response

IgG

which antibody is most abundant in serum

IgG

which antibody crosses the placenta

IgG

which antibody is prominent in breast milk

IgA

what is secretory IgA’s structure

dimer

what is the main function of secretory IgA

immune exclusion

which antibody is associated with allergies

IgE

which cells are especially associated with IgE responses

mast cells, basophils, eosinophils

what is IgD mainly associated with

immature/naive b cells

IgG1 vs IgG2

IgG1= strong opsonization/complement; IgG2= poorer

IgM vs IgG shortcut

IgM= first; IgG=stronger secondary response

maternal immunity shortcut

IgG… placenta; IgA… breast milk

what tyoe of antigen does MHC I present

endogenous antigen

MHC I presents antigen to which t cell

CD8+ t cells

What type of antigen does MHC II present?

exogenous antigen

MHC II presents antigen to which T cell?

CD4+ helper t cells

Which cells mainly express MHC II?

Dendritic cells, macrophages, B cells

Which cells mainly express MHC I?

nearly all nucleated cells

Exogenous antigen pathway?

Uptake → degradation → MHC II → CD4

Endogenous antigen pathway?

Cytosolic protein → proteasome/TAP → MHC I → CD8

what is cross-presentation

exogenous antigen presented on MHC I

What can autophagy allow?

Intracellular antigen to enter the MHC II pathway

What does a TCR recognize?

peptide+ self MHC

what is a superantigen

molecule that activates many t cells by binding MHC/TCR outside the normal cleft

what can superantigens cause

massive cytokine release/ cytokine storm

examples of superantigens

S aureus entertoxins, TSST-1, Streptococcal pyrogenic exotoxins

what is signal 1 for CD4 t cell activation

MHC II peptide binds TCR with CD4

What is Signal 2 for T-cell activation?

CD80/86 on APC binds CD28 on T cell

What happens if Signal 1 occurs without Signal 2?

anergy

what is anergy

functional unresponsiveness of a t cell

What happens during negative selection?

Strongly self-reactive T cells are deleted

What happens during positive selection?

T cells that can recognize self-MHC survive

Where do positive and negative selection occur?

thymus

what does CD8 bind

MHC I

what does perforin do

forms pores in the target cell membrane

what do granzymes do

trigger apoptosis of the host target cell

what do granulysin do

kills bacteria

perforin/granzyme vs. granulysin shortcut?

Perforin/granzyme = host apoptosis; granulysin = bacteria

What is Th1 mainly associated with?

Intracellular pathogens and macrophage activation

Main Th1 cytokine?

IFN-gamma

What is Th2 mainly associated with?

Humoral immunity and extracellular pathogens

important Th2 cytokines?

IL-4, IL-5, IL-9, IL-10, IL-13

What can IL-4 promote?

IgE responses and b cell activity

what is Th17 mainly associated with

inflammation and defense against bacteria/ fungi

IL-17

recruits neutrophils

IL-22

promotes epithelial antimicrobial peptides

what is treg mainly associated with

immune suppression and self tolerance

important treg cytokines

TGF-beta and IL-10

memory t cells

respond faster and more strongly on reexposure

M cells in mucosal immunity

transport lumen antigens to underlying immune cells

what antibody is central to mucosal adaptive immunity

sIgA

T-dependent vs. T-independent?

T-dependent = memory; T-independent = no memory

IgG vs. IgA maternal immunity?

IgG = placenta; IgA = breast milk

MHC I vs. MHC II?

MHC I = endogenous/CD8; MHC II = exogenous/CD4

Signal 1 vs. Signal 2?

Signal 1 = antigen recognition; Signal 2 = co-stimulation

Negative vs. positive selection?

negative deletes strong self-reactivity; positive preserves self-MHC recognition

Th1 vs. Th2?

Th1 = intracellular/macrophage; Th2 = humoral/extracellular

Th17 vs. Treg?

Th17 = inflammation/neutrophils; Treg = suppression/tolerance

IgM vs. IgG?

IgM = first; IgG = dominant secondary response