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Immunology Lecture 3
B cells & Antibodies
32
Immunology
Graduate
10/18/2012

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Term
Cellular Immunity
Definition
Ag in cytosol --> MHC I --> CD8+ --> kills cell
Term
Humoral Immunity
Definition
Ag in Vesicle --> MHC II --> CD4+ --> B cells --> plasma cells --> antibodies
Term
Monomeric Immunoglobulins
Definition
IgD, IgE, IgG, and sometimes IgA (in blood)
Term
IgA
Definition
Found in dimeric form in gut and external secretions
Term
IgM
Definition
Can be pentameric, first responder in immune response
Term
IgG
Definition
IgA1-4 subclasses depends on hinge arragement
IgA2 CANNOT crosss placenta
Term
Funtional regions of the IgG molecule
Definition
variable regions (heavy and light chain)
Term
Papain + IgG =
Definition
3 fragements: 2 FAB and 1 Fc
Term
Pepsin + IgG =
Definition
2 fragements : FAB and Fc
Term
Mercaptoethanol + IgG =
Definition
4 fragements: 2 heavy chains and 2 light chains
Term
Epitope
Definition
a portion of an antigenic molecule that is bound by an antibody or gives rise to the MHC-binding peptide that is recognized
Term
Affinity
Definition
the measure of the strength with which one molecule binds to another at a single binding site
Term
Avidity
Definition
is the overall strength of binding of an antibody to its antigen with multiple sites, in contrast to affinity, which is the strength of binding at one single site
Term
Somatic Recombination
Definition
DNA recombination that occurs between gene segments in the immunoglobulin genes in developing B cells. It generates a complete exon composed of a V gene segment and a J gene segment that encodes the variable region of an immunoglobulin. The RAG-1 and RAG-2 genes encode VDJ recombinase which makes random recombinations of heavy and light chains and random arragements of V, D and J sequences
Term
Generation of Junctional Diversity
Definition
During the process of gene rearrangement the addition or removal of P and N nucleotides added to gene segments which code for the hypervariable regions produces diversity
Term
Differential splicing of mRNA
Definition
exons of the RNA produced by transcription of a gene are reconnected in multiple ways during RNA splicing. The resulting mRNAs are translated into different protein isoforms
Term
Allelic exclusion
Definition
When a B cell interacts with an antigen, this activates and engages a subset of B cells in the population specific to that antigen. In developing B cell only one heavy chain and one light chain can be expressed so that B Cells have ONE antigen that they are specific to Allelic exclusion occurs by the RAG genes being stopped to halt somatic rearrangement. Only one of the two C-region alleles at the immunoglobulin heavy chain or light chain loci is expressed in each B cell.
Term
Somatic hypermutation
Definition
mutation in the B cell DNA which results in a production of strong antibodies for an antigen. o Positive selection selects for the immunoglobulin with the strongest affinity to further differentiate into plasma cells and produce antibodies
Term
Isotype switching
Definition
involves a somatic recombination process that attaches a different heavy-chain constant-region to the existing variable region exon, this enables the B cell to switch it's immunoglobulin without losing antigen specificity.
Term
Affinity maturation
Definition
occurs as the result of somatic hypermutation of the rearranged immunoglobulin region and the consequent selection of mutated B cells that make antigen receptors of higher affinity for their antigen.
Term
B cell differentiation
Definition
Pro- B --> Pre-B --> Immature B --> Mature naive B --> Activated B --> Plasma Cell or memory B cell
Term
Pro B Cell
Definition
rearrangement of heavy chain
N nucleotides added
pre-B cell receptor
allelic exclusion in heavy chain
Term
Pre B Cell
Definition
rearrangement of light chain
allelic exclusion of light chain
IgM synthesized
Term
Immature B cell
Definition
IgM expressed
negative selection of auto-immune B cells
Term
Mature Naive B Cell
Definition
IgD expressed in addition to IgM
Term
Activated B Cell
Definition
antigen primed
clonal expansion (positive selection)
Term
Plasma Cell
Definition
producing antigen specific antibodies
Term
Memory B cell
Definition
adaptive immunity
Term
B Cell differentiation in the Bone marrow
Definition
Pro- B, Pre- B, and Immature B
Term
B cell differentiation in the peripheral lymphoid organs
Definition
B cell, activated B cell, plasma cell, B cell with isotypes and Memory B cell
Term
T Helper Cell induced B cell activation (5 parts)
Definition
(1) Cross linking of BCR and co receptor with antigen (2) Chemokines hault movement from T zone (3) B cells present degraded antigen to T helper cells (4) T helper cells present via MHC II to other B cells to produce antibodies against the antigen (5) IL-4 is essential for B cell proliferation and differentiation
Term
Thymus Indepdent B cell Activation
Definition
antigens are expressed on the pathogen at such a high density that is can cross-link with the B cell antibody and co receptor without any need for additional signals. This induces an early immune response and there is no affinity maturation because no somatic hypermutation
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