Lec 15: B cells and Isotypes Flashcards
BcR coreceptors
non-covalent association with coreceptors CD21, CD19 and CD81
CD21 can bind antigen coated with complement protein C3d for cooperative binding with BcR
CD19 and CD81 participate in BcR signal Transduction (do dis with their cytoplasmic tails)`
What are the TcR coreceptors
CD3 and CD4
or
CD3 and CD8`
Antibody isotypes of mammals
iga igd ige igg igm
note, iga and igm contain an extra polypeptide calle da J -chain which linkes the polymeric units together
iga
two types
found in mucosal areas, such as the gut, respiratory tract and urogenital tracts.
Prevents colonization by pathogens.
Also found in the saliva, tears, and breast milk
dimer
igd
one type
functions mainly as an antigen receptors on B cells that have not been exposed to antigens.
It has been shown to activate basophils and mast cells to produce antimirobial factors
monomer
ige
one type
binds to allergens and triggers histamine release from mast cells and basophils, and is involved in allergy.
also protects agaisnt parasitic worms
monomer`
igg
four types
in its four forms, provides that mahority off antibody based immunity agaisnt invading pathogens.
The only antibody capable of crossing the placenta to give passive immunity to the fetus
monomer
igm
one type
expressed on the surface of b cells and in a secreated form with high avidity
eliminates pathogens in the ealty stages of B cell mediated (humoral) immunity before ther is sufficient igg
Serotype conversion during infection
primary igm response proceeds igg response (primeary with igm and secondary infections with igg)
Igg response persists monthes to years after infection
igg levels are boosted after secondary infection
CSR: Class Switch Recombinaiton
results in produciton of high-affinity antibodies (from somatic hyper mutation) with different isotypes
this is an irreverible process, by can occur more than once in a single cell (*because it involves the loss of DNA)
occurs in sequential order
= igm => igg => ige => iga
Tcell mediated signals promote isotype switiching in Bcells
eaach subtype of T helper cells secrete diffeent cytokines
specific cytokines promote isotype switiching in Bcells
cytokines in mucosal lyphoid tissue promote switching to iga
give an example of Thelper mediated class switching in bcells
see slides
helper Tcells secrete cytokines and bind with CD40L
= cyt = IFNg
igg subclss igg1 and igg3
principle effector function = Fc repector dependent phagocyte responses, complement activation, and neonatle immunity (placental transfer)
helper T cells secretion of Il-4 = class swith to Ige
principle effector funciton
= immunity agaisnt helminths as well as mast cell degranulation (immediate hyper sensitivity)
FcR bind different antibody isotypes
FcR allows nonh-spedific immune cells to utalize the specificity of antibodies to direct responses agaist antigens and pathogens
this is a bridge between humoral and cell mediated immune responses
FcR binding by an antibody does not trigger signalling
-> cross linking and oligomerization of FcRs by immune complezes (=antibodies = antigens) initates ITAMS or inhibits ITIMS effector responses
cell-tyype specific expression of FcRs
basophils, mast-cells and seoisinophiles use IgE
Required reading ***
chapter 13, p. 481-500
how do antibodies protect us at mucosal surfaces
how are antibodies secreted at mucosal surfaces
