Humoral Immunity Flashcards
Humoral Immunity is mediated by ______ and secreted _______
B lymphocytes; antibodies
Function of Antibody
Block the ability of microbes or their secreted toxins to bind to and infect or damage host cells
What molecules of the B Cell receptor recognize antigens
Immunoglobulin (Ig)
Epitope
That part of a native protein, lipid, or lipoprotein antigen that is recognized by B lymphocyte antigen receptors
Difference between BCR and TCR constant regions
BCR can change - alters effector functions
TCR is fixed
Affinity for antigen for BCR
BCR has higher initial affinity (Compared to TCR) which increases during response
Difference between checkpoints of T-cell and B-cell development from common lymphoid progenitor
none
Recombination events for BCR antigenic diversity
1) First recombination event is the heavy chain D and J exons
2) Second recombination of V with DJ
3) VDJ recombination of a IgH (heavy chain) constant (Cμ) region gene segment
4) The heavy chain transcript (VDJC) is then processed and expressed within the cell, and then at the cell surface with a surrogate light chain
At the Pre-BCR stage, there is a ___________ which helps ___________ the heavy chain
Surrogate light chain; stabilize
Fab Region
Region on antibody that binds to antigens
Fc region
the tail region of an antibody that interacts with cell surface receptors
The diversity region is only expressed:
In IgH chain transcript (chromosome 14)
Antigenic Diversity (2 types)
Combinatorial - variation amongst possible VDJ and VJ exon combinations
Junctional: Removal of nucelotides and addition of nucleotides by TdT enzyme
Hypervariability in IgH and IgL
CDR1, CDR2, CDR3
Differentiation of B-Cells (4 types)
1) Effector Cells: antibody-secreting plasma cells
2) IgG-expressing B cell
3) High-affinity Ig-expressing B cell
4) Memory B Cell
During the induction phase, antigens are first presented to:
Membrane bound IgM on Naive B cells
3 types of lymphocyte subsets
Follicular B cells
Marginal zone B cells
B-1 cells (mucosal tissues, peritoneal cavity)
2 signals for Naive B cell activation
1st signal: BCR binds Antigen
2nd signal: CR2/CD21 (complement receptor) activated by C3d complement protein OR TLR activated by microbial pathogen associated molecule pattern (PAMP)
ITAM
Immunoreceptor tyrosine-based ACTIVATION motif
First part of B cell Receptor activation
Two or More BCRs must be cross linked by antigen to become activated
Two types of effector B cells
T-Independent: differentiation occurs in the absence of T cell help
T-dependent: T cells provide additional helper stimuli during B cell differentiation (typically protein antigen)
Activation of Naive B cells causes:
1) Entry into cell cycle: mitosis
2) Increased expression of cytokine receptors
3) Migration out of lymphoid follicles
4) Low-level IgM secretion
Presentation of Antigen to T cell by B cell (5 Steps)
1) B cell recognition of native protein antigen
2) Receptor-mediated endocytosis of antigen
3) Antigen processing and presentation
4) T cell recogntion of antigen
5) Activation of B cells by CD40 ligand and cytokines - proliferation and migration back to germinal center
Class switching
Results in antibodies with Fc regions capable of diverse effector functions
Affinity maturation
Produces antibody with higher affinities for antigen binding (triggered by prolonged or repeated antigen stimulation)