PCB4233 Immunology Exam 4
What are the different types of B-cell responses and what antigens induce them? - *answers
*For example B cell types (TI-1, TI-2, TD) and antigen (Soluble Protein antigens, Bacterial Cell
wall components, Capsular polysaccharides). Remember TI (T cell independent), TD (T cell
dependent)
T-dependent responses require help from T cells: Are typically generated upon recognition of
protein Ag
T-independent responses do not require T-cell help: Generated upon exposure to
multivalent/polymerized Ag- TI-1 Ag bind to B cells through PRRs and mIgs or TI-2 Ag cross-link
large numbers of BCRs
What receptors on T cells help activate B cells? - *answers *CD40L on T cells; CD40 B cells
B-cells bind Ag via BCR
Name the chemokines that B cells follow as they become activated and migrate through
secondary lymphoid tissue. - *answers *CXCR5 receptor binds to CXCL13 expressed by FCDs in
the B-cell follicles (cortical region of the secondary lymphoid tissue).
Upon finding antigen CCR7 receptor binds to CCL19 and CCL21 secreted by stromal cells in the T-
cell zones and the B cell moves in the boundary between the B-cell and T-cell zones.
What cytokines are required for survival of B cells in secondary lymphoid tissue? - *answers
*Require CD40/CD40L interactions between B/T cells Cytokines from FDCs and TFH cells
stimulate proliferation further
When are the different Immunoglobulin isotypes produced during an immune response and
how do they differ? - *answers *Plasma cells are Ig-producing machines:
Surface Ig is near zero, but secreted Ig values are high
Found within first 5-6 days of immune responses in medullary cord regions of lymph nodes
, PCB4233 Immunology Exam 4
What occurs in the germinal center? - *answers *Somatic hypermutation (SHM)/affinity
selection occur within the germinal center; Class switch recombination (CSR) occurs within the
GC after antigen contact
SHM (Somatic hypermutation) - *answers *-SHM produces individual point mutations in Ig
heavy- and light-chain rearrangements:
Mutations increase over time and with repeated exposures
Followed by affinity selection result in increased affinity for Ag over time
-AID-mediated somatic hypermutation:
Activation-induced cytidine deaminase
Produces opportunity for mutation by altering deoxycytidine bases
-Mutational apparatus targeting:
Mutational hot spots are sequence motifs far more likely to be targeted
Include DGYW/WRCH sequence motif
This prevents mutations in non-Ig areas
-Ag-induced selection of B cells with higher affinity:
B cells that can bind, process, and present more Ag to T cells for cytokine assistance survive
Higher-affinity B cells may actually steal Ag from lower-affinity B cells, promoting their own
survival signals
class switching mechanism - *answers *-AID initiates CSR processes (just as in SHM) by
deaminating C bases in single-strand DNA dislocated by germ-line transcripts
-DNA uridine glycosylase removes the U base created by AID
-Endonucleases nick the DNA backbone at the a basic sites at multiple points
-Mismatch repair enzymes convert single-strand breaks into double-strand breaks
-Double-strand break repair machinery repairs the breaks by cutting out the intervening DNA
What are the different types of B-cell responses and what antigens induce them? - *answers
*For example B cell types (TI-1, TI-2, TD) and antigen (Soluble Protein antigens, Bacterial Cell
wall components, Capsular polysaccharides). Remember TI (T cell independent), TD (T cell
dependent)
T-dependent responses require help from T cells: Are typically generated upon recognition of
protein Ag
T-independent responses do not require T-cell help: Generated upon exposure to
multivalent/polymerized Ag- TI-1 Ag bind to B cells through PRRs and mIgs or TI-2 Ag cross-link
large numbers of BCRs
What receptors on T cells help activate B cells? - *answers *CD40L on T cells; CD40 B cells
B-cells bind Ag via BCR
Name the chemokines that B cells follow as they become activated and migrate through
secondary lymphoid tissue. - *answers *CXCR5 receptor binds to CXCL13 expressed by FCDs in
the B-cell follicles (cortical region of the secondary lymphoid tissue).
Upon finding antigen CCR7 receptor binds to CCL19 and CCL21 secreted by stromal cells in the T-
cell zones and the B cell moves in the boundary between the B-cell and T-cell zones.
What cytokines are required for survival of B cells in secondary lymphoid tissue? - *answers
*Require CD40/CD40L interactions between B/T cells Cytokines from FDCs and TFH cells
stimulate proliferation further
When are the different Immunoglobulin isotypes produced during an immune response and
how do they differ? - *answers *Plasma cells are Ig-producing machines:
Surface Ig is near zero, but secreted Ig values are high
Found within first 5-6 days of immune responses in medullary cord regions of lymph nodes
, PCB4233 Immunology Exam 4
What occurs in the germinal center? - *answers *Somatic hypermutation (SHM)/affinity
selection occur within the germinal center; Class switch recombination (CSR) occurs within the
GC after antigen contact
SHM (Somatic hypermutation) - *answers *-SHM produces individual point mutations in Ig
heavy- and light-chain rearrangements:
Mutations increase over time and with repeated exposures
Followed by affinity selection result in increased affinity for Ag over time
-AID-mediated somatic hypermutation:
Activation-induced cytidine deaminase
Produces opportunity for mutation by altering deoxycytidine bases
-Mutational apparatus targeting:
Mutational hot spots are sequence motifs far more likely to be targeted
Include DGYW/WRCH sequence motif
This prevents mutations in non-Ig areas
-Ag-induced selection of B cells with higher affinity:
B cells that can bind, process, and present more Ag to T cells for cytokine assistance survive
Higher-affinity B cells may actually steal Ag from lower-affinity B cells, promoting their own
survival signals
class switching mechanism - *answers *-AID initiates CSR processes (just as in SHM) by
deaminating C bases in single-strand DNA dislocated by germ-line transcripts
-DNA uridine glycosylase removes the U base created by AID
-Endonucleases nick the DNA backbone at the a basic sites at multiple points
-Mismatch repair enzymes convert single-strand breaks into double-strand breaks
-Double-strand break repair machinery repairs the breaks by cutting out the intervening DNA
