adaptive immunity - b and t lymph

phase 1 b cell dev

developing bc acwuire funcitonal bcr thru ordered arrangement of ig genes

phase 2 b cell dev

b cells whse ig receptor binds to self are elimnatede - neg sel

phase 3 - b cell dev

remaining b cells w functional receptor leave bone marrow and move into secondary lymphoid tiss - pos selection

phase 4 - b cell dev

search for infection — non self specific antigen

phase 5 b cell

contact w antigen, ativation nad clonal expansion

phase 6 - b cell dev

attack infection by diff into antibody secreting plasma cells, and memory b cells

how many epitopes does a b cell respond to

one

clonal selection theory

multiple lymph w diff speciaitlies - clonal deletion (deleltion of self reactive clones) - clonal selection - clonal expansion (prolif)

forms of ig that bind to infectious agent

surface and secreted

surface ig

emedded in b cell mem, acts as antigen receptor

secreted ig

secreted by activated plasma b cells -antibodies

ig structure

2 identical heavy chains and 2 identical light chians with constaint and vairbale regions

fc vs fab region

fc at stalk of y — composed of only constant, and top of y is fab w constant and avriable region

hinge in antibody allows

flexibiliy and non-rigidity - look for epitopes via moving and floating

ig variable region - heavy chain encoded by

variable, diversity and joining

ig variable region - light chain encoded by

variabel adn joining region

other methods of diveristy in ig

random deletions and insertions in joinig of heavy and light chain - junctional diversity

what determines class of ig

heavy chain constant region gene segment

effector funciton of antibody derived from

constant (fc) region

igm

first made, naive b cells - pentamter linked by j chain, activate complement and neutralise pathogen

igg

cross placenta (fc), activate complement, small enough to diff into tissue, major ig

iga

dimer by j chain, prominent in mucosal secretions to protect in airways, gut, bm

ige

respond to parasites via degran (fc) mediate allergic reactions

igd

expressed on naive b cells - not usually secreted

effector func of antibodies

precpitation, complement fixation, agglunation, opsonisation, neutralisation

fab

neutralise path/toxins (igg, igg), musocosal immun. (iga)

fc - opsonisation

igg - fc region binds to fc receptor on phag

fc - classical pathway

igm, igg, triggers cascade

fc - antibody mediated cell cytotoxicity

igg - ofnk cells

t cell dev - step 1

hematoopooiietic stem cells in bone marrow migrate to thymys

t cell dev - step 2

t cells undergo thymic education in the thymys

t cell dev - step 3

mature naive t cells translocate to peripheral lymphoid tissue

t cell dev - step 4

actiavted, naive t cells become effector t cells that can mount immune responses

t cell education - pos selection

if the tcr has no capacity to bind self mhc molecules, t cell dies

t cell education - neg selection

if tcr binds host mhc/peptide complexes present in thymus too tighly, t cell dies (remove autoreactive)

chains t cell receptor

heterodimer of alpha and beta chain

tcr alpha domain gene segements

v,j - one c

tcr beta domain gene segments

v, d, j - one c

what do tcr recognise

protein antigens that have been degraded or processed into short peptidse - requires proteolysis

mhc class i cellls

almost all nucleated - recog by cd8

mhc class ii cells

only expressed on macrophages, b cells and dc (apcs) - reocg by cd4

mhc i presentation

peptdes largely derived from endogenous, peptides via proteolysis in cyto, enter er via tap load into mhc1 in lumen of er, go to surface

mhc ii presentation

peptides derived from exogenous, via endosomal network, to endosome, fuse and release contents in mhc-ii enriched compartment, where meets mhc ii from er, and travels to surface

dc activation leads to

increased surface expression of mhci/ii, secretion of cytokines, and expression of costim

activation of dc in secondary lymph

dc pick up antigen and move to draining lymph vessel, settle in t cell area in lymph node

activated dc to naive t cells- signal one

display pathogen peptides on MHC

actiavted dc to naive t cells - signal two

express co stim (cd80, cd86)

activated dc to naive t cells - signal three

secrete selected cytokines