All of the following are part of Fab region of Ig except?
VH
VL
CH 2
CL
VH and VL determines the idiotype and CH2 and CH3 determine the isotype of Ig
Antigen Binding site
Specificity is determined by hypervariable regions within the variable domain
Each variable region has 3 hypervariable regions called complementary determining regions (CDRs)
An antigen binding site is composed of 3 light chain CDRs and 3 heavy chain CDRs
All of the above are true
None of the above
Ig Determinants
Isotypic : constant domain, present in all individuals of a species
Allotypic: constant domain; different alleles within a species
Idotypic: antigen binding site
all of the above are true
1&2 are true
Antibodies interact with molecules by the Fc receptors (constant region)
Regarding different classes of Ig a
IgG - Monomer - circulating - Most abundant in serum - crosses transplacentally via brambell receptor
IgM - Pentamer - Surface of B cells or circulating - Ag receptor on B cell - First class of Ab released by B cells during primary response
IgA - Monomer - Surface of B cells - Important for B cell activation - Co-expressed with IgM on B cells due to differential RNA splicing
IgD - circulating monomer, secreted dimer - circulating in plasma or secreted in saliva ,tears, milk etc - protects mucosal surfaces
IgE - Monomer - circulating or cell bound - found in mast cells and basophils - High affinity IgE receptors binds in the absence of Ag
All are correct
1,2,5 are correct
3,4 are correct
All are wrong
Regarding Pro-B cell all are true except?
No Ig is expressed
Recombination Signal Sequences (RSS) & 12/23 rule regulate arrangement & ensure that proper joining occurs: D-J --> V-DJ
RAG1/RAG2 recognised and binds to Il-7R
Palindromic nucleotide addition at hairpin loop formation by DNA polymerase
Non-template nucleotide addition at hairpin loop formation by TdT
Regarding Pre-B cell
IgM expressed
Allelic Exclusion: RAG1/RAG2 is repressed to stop VDJ rearrangement of H locus
RAG1/RAG2 is re-expressed for VJ rearrangement - Somatic Recombination - of each daughter cell's L chain
Kappa light chain recombines 1st
all of the above are correct
Immature B cell - all are true except
IgG expressed
Negative Selection for Tolerance - Immature B cell with no self reaction will continue on to maturity and leave the bone marrow
Light chain rearranges for a chance to make BCR with new specificity
Immature B cell binds multivalent self-antigen and fails receptor editing --> Clonal deletion (apoptosis)
mmature B cells bind soluble self-antigen --> Clonal anergy
Mature B cell express IgM + IgD due to differential RNA splicing
CD21 co-receptor binds Fc of Ig (ITIM) - positive co-receptor --> activation FcyR binds to C3d - negative co-receptor --> no activation
Following is the sequence of events 1st T_B cell interaction - all of the following are true except?
Antigen activated B cell (APC) migrates toward T-B boundary and present antigen by MHC II to CD4+ Helper T cell
CD40 activates T Helper to express CD40-L and cytokines
CD40-CD40-L bind and T Helper releases cytokines toward B cell
Mutated CD40-L results in X-Linked agammaglobulinemia
Proliferation of activated B cell to form germinal centers (Clonal expansion)
AID (Activation Induced Deaminase) inserts point mutations in the variable regions of BCR for diversification of BCR
All of the following regarding 2nd T-B cell interaction are true except?
Class/Isotypic Switching : The constant region of the heavy chain undergoes change of Ig Isotype but the selected variable region stays the same maintaining antigenic specificity and affinity
Isotype is determined by cytokines released from Helper T cell
Enables the same assembled Vh exon to be associated with different CH genes in the course of an immune response thus increasing the divrsity of Ig function
Il-4 secreting T cell stimulate Plasma cell production and Il-10 secreting T cell stimulate memory B cell production
Thymus independent response the antigens are polysaccharides and the antibody made is always IgM because there is no class switching, no affinity maturation and no memory cell formation
MHC Class I is expressed on the surface of all nucleated cells including RBC
Endogenous pathway MHC I and Exogenous pathway MHC II
Antign processing is proteolytic deradation of proteins into peptides of a suitable size for binding to MHC Antigen Presentation - actual display of the processed peptide bound to MHC molecules on the surgace of an APC or target cell
T cell recognize non linear and conformational determinants
Dendritic cells are exception to the rule - Cross presentation allows exogenous proteins to be presented on MHC I and endogenous proteins to be presented by MHC II by autophagy
Viral proteins interfere with MHC I
Inhibit peptide transport
Inhibit peptide loading
Cause MHC I degradation
all of the above
none of the above
Intracellular bacteria evade MHC II by
Escape endosomes
Neutralize endosome acidification
Block fusion with lysosomes
Sequesters MHC II molecules after vesicle fusion
All of the above
