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-terminally differentiated B cells
-short lived (usually 3 to 6 days)
-Over 40% of the total proteins produced are antibodies.
-Specificity of the Igs produced are identical to that of the BCR of the parent B Cell
large, homogenous immunoglobulin-containing inclusions usually found in a plasma cell undergoing excessive synthesis of immunoglobulin
-tumor of plasma cells arising as a result of a random mutation in a single B-cell
-continues to produce specific antibody (referred to as myeloma protein or M protein) that is indistinguishable from normal antibody moleucles
Isotype (Class switching)
Change in antibody class that occurs during the course of an immune response to a protein antigen as a result of heavy chain gene switching
-Does not change antibody specificicty, but changes the effector functions an antibody can perform
Somatic Mutations (Affinity Maturation)
-process that results in an increae in the affinity of specific antibody for its antigen and is the result of somatic mutations of the previously rearranged Ig V (D) J genes, followed by selective survival of the B cells producing the antibodies with the highest affinity
-occurs only in humoral immune responses to protein antigens
-Follicular dendritic cells
-found in the lymphoid follicles of the lymph nodes. spleen and MALT
-Expres Fcϒ receptors (CD32) and complement receptors
-nonphagocytic and do not present antigen to helper T cells
-Trap immune complexes and assist in B cell maturation by the presentation of intact antigen to the B cells. This occurs in the germinal centers of peripheral lymphoid organs and induces class switching and proliferation.
-Result is a population of B cells that become memory B cells with high affininty BCRs or B cells that produce antibodies with significantly higher affinities for antigen
Memory B Cells
-functionally quiescent long lived cells
-development requires presence of T cell-derived cytokines
-express high-affinity Ig receptors of switched isotypes
-antigentic doses required for stimulating memory cells are lower than those for naive B cells
-Account for the accelerated production of large quantitites of isotype switched, high affinity Igs after secondary exposure to the same agntigen
Response of B cells to T-independent antigens
-T-independent antigens bind directly to B cells
-large doses is required to illicit a response
-Mostly IgM antibodies are produced at low affinity
-No significant signs of class switching, affinity maturation or memory
Clonal Selection Theory
-explains why antibodies are produced only to those antigens to which an individual is exposed
1) lymphoid stem cells differentialte randomly to produce clones of lymphocytes, each of which is committed to respond to a single atigenic determinant
2) Antigen binding to lymphocyte receptors triggers then to proliferate and differentiate into plasma or memory cells
3) the specificity of antibodies produced by a lymphocyte is identical to that of its antigen receptor
4) lymphocytes bearing receptors specific for self-peptides are deleted (negative selection) at an early stage in development
-substances that non-specifically induce DNA-synthesis and cell division, therefoe stimulating the proliferation of many different clones of lymphocytes
-often used to stimulate lymphocytes and therefore assess immune function
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