Humoral immunity and B cell effector mechainsm

Question 1

what are the types of B cell activation?

Answer 1

T dependent activation : which basically agianst protien ag and has more class switching and affinity maturation
T-independent activation: against non-protein protien antigen like polysaccharides, multivalent ag and lipids and nucleic antigens

Question 2

What are the types of B cells?

Answer 2

Follicular B: in lymphoid organ follicle and make long-lived plasma cells
Marginal Zone B cells: in periphery of splenic white pulp and outer follicle of LN and it recognize blood-borne antigens and sacchrides antigens and mainly produce IgM
B-1 Cell: against multivalent antigen and mostly produce IgM

Question 3

mechanism of activation of B cell by antigen

Answer 3

A B cells with agR recogize 2 or more ag presented by APCs; this causes the 2 adapter proteins IgAlpha and IgBeta which contain ITAM to activate Syk tyrosine kinase and it phopshrylates tyrosine residues on adaptor protiens which activates TF for B cell

Question 4

How innate immunity activate B cell

Answer 4

1- by complement fragment C3d recognized by CR2 which activates ITAM and Syk tyrosine kinase
2- PAMPs which activates ITAMs and syk tyrosine kinase

Question 5

what are receptors found on B cell

Answer 5

1- TLR
2- Complement R( C3d)
3- IgR
4- MHC1 and MHC2
5-FcR
6- CD19 and CD20

Question 6

Antibody feed back inhibtion

Answer 6

when Ig for example IgG binds to FcyR2B receptor on B cell causing activation of ITIM which block B cell receptor signaling

Question 7

how does the Th cell help in HMI?

Answer 7

when DC present an antigen in the T cell zone in LO, to Th cells it migrates to the parafollicular areas and it decreases the secetion of CCR7 and increase secretion of CXCR5 and at the same time when B cell is activated by an Ag it increases secretion of CCR7 but inhibits CXCR5 making an attraction force and closing to each other

Question 8

How Th cells activate B cell

Answer 8

by binding the CD40L of T cell to CD40 on B cell and Cytokine from Th cell to cytokine receptor on B cell and i will induce affinty maturation, class switchig and profiration

Question 9

Class switching Function

Answer 9

it is induced by cytokines and CD40L-CD40 interaction
1- forming IgG1 and IgG3 which bind to fcyR1 activating B cell causing phagocytosis and opsinization and secretion of IFNy, IL4 or IL17 and IL21 and IL10
2- against helminth by secretion of IgE which has FceR whicn eosinophil bind to
3- IgG bind to FcRn in placenta

Question 10

Class switching mechanism

Answer 10

Cu heavy chain bind to ligh chian and make IgM and thn by AID enzyme transfering Cytosine to uracil in the DNA it makes DNA with nicks and the DNA repair and by help of Tfh cells it make different Igs

Question 11

what interlukines make IgG

Answer 11

IL4
IL10
IFNy
TGF-B

Question 12

what interlukines make IgA

Answer 12

TGF-B and BAFF

Question 13

what interlukines make IgE

Answer 13

IL4 from TfH cells which are activtaed by IL5

Question 14

How does B cell neutrlize pathogen

Answer 14

1- Block entry
2-Block transmission
3- neutrlize endo and exotoxins

Question 15

What is the mechanism of opsinziation and phagocytosis

Answer 15

when an encapsulated bacteria is surrunded by Ig mainly IgG the IgG bind to FcyR1 on neutrophil and macrophage (CD64) when ingest the bacteria and make phagolysosome and cause destruction
and it inhibited with Ig bind to FcyR2B (CD32)

Question 16

where does FcyR1 and FcyR2 present

Answer 16

FcyR1 on macrophage and neurotphil
FcyR2 on neutrophil, macrophage, DC, mast cells and B cells

Question 17

what is the mechainsm of Antibody dependent cellular cytotoxicity

Answer 17

enveloped virus surrouned with Ig mainly IgG binds to FcyR3 CD16 on NK cells causes secretion granzymes and perforins causing killing

Question 18

machanism of defense against parasites and helminth

Answer 18

eosinophil has FceR1 where IgE will bind causing it activation
eosinophil secretion is increased by IL5 from Th2 cells
eosinophil will secrete MBP. eosinophil peroxidase and eosinophil derived neurotoxin

Mast cell will have FceR1 receptor where IgE will bind whci will cause IL secretions

Question 19

what IL are secreted from Mast cell

Answer 19

IL4 increase IgE and Th2
IL5. activate eosinophil
IL13 attract eosinophil
TNFalpha increase permeability and migration
IL33 increase Th2 cytokines
chemokine recruitng leukocytes

Question 20

what will C3 deficincy cause

Answer 20

increase suscpetibility to bacterial infection

Question 21

what will C2 and C4 deficincy cause

Answer 21

increase infection and SLE% due toaccumlation of immune complexes

Question 22

what will C9 and MAC deficncy cause

Answer 22

increase Neisseria infection

Question 23

what will happen to complement system due to spleenctomy

Answer 23

decrease macrophagoe phagocytosis and decrease in IgM causing inhibiton of classical pathway causing recurrent infection by encapsulated bacteria

Question 24

what will deficincy in C1 inhibitor cause

Answer 24

Heredatory angiodema

Question 25

what is the pathology of heredatory angiodema caused by C1 INH def

Answer 25

increase in complement activation and kallikrein breakdown to bradykinin causing edema

Question 26

what is the pathoglogy of paraxyma nocturnal hemoglobinemia

Answer 26

increase in complement activate on eyrthorcytes causig thier lysis and it is due to decrease DAF and CD59what

Question 27

what will Factor I and Factor H deficncey cause

Answer 27

Atypical hemolytic uremic syndrome
increase in complement activation
age related macular degenration

Question 28

what will decrease of properdin do and why

Answer 28

properdin stablizes C3 convertase so when it deficinet there will be no MAC formed so will increase susceptibility to nisseria infection