Immunology: B Cells

Adaptive Immunity: involves B lymphocytes

Small proportion of circulating lymphocytes, ONLY cell which produces antibodies, APC

B Cell Surface Markers

B Cell Receptor (BCR) = Ig receptor (sIg), Fc receptor, CD19, CD20, CD21, MHC II

B1

CD5

B2

Most B cells in adults

B Cells Maturation

Occurs in bone marrow, starts with a hematopoietic stem cell that develops into an early lymphocyte progenitor

Antigen indepenent

Maturation into immunocompetent B cells

Antigen dependent

Activation of B cells by antigen, differentiation of activated B cells into antibody-producing plasma cells

Antigen Independent B Cell Differentiation

Formation of several distinct, chronological subpopulations in the bone marrow: pro-B (progenitor), pre-B (precursor), immature B, mature B, develop B cell receptor (BCR), surface Ig

Pro-B Cells

Rearrangement of genes that code for heavy and light chains of BCR (and antibody molecules)

C-Kit receptor on pro-B cells interacts with cell surface molecule (stem cell factor) on _______ cells

Stromal

What does pro-B rearrange first

Heavy chain (random)

Successful rearrangement of one set of heavy chain genes in pro-B cells

μ first and δ chains later

Pre-B Cells

Synthesis of H chains, μ chains accumulate in cytoplasm, express μ chains on cell surface with a surrogate light chain molecule

Pre-b cells have ____ short polypeptide chains non covalently associated with each other, along with 2 shorter chains (Ig-α,

Ig-ß) that signal transduction

2

2 heavy chains, Ig-α, Ig-ß, surrogate light chain

=Pre-BCR

Immature B Cells

Complete IgM on surface (sIgM) = complete BCR, indicates successful rearrangement of light chain genes, monomer, variable regions on light and heavy chains

Immature B cells express other surface proteins

CD19, CD20 (since pro-B), CD21 (complement receptor), CD40 and MHC II (interaction between B & T cells)

Mature B Cells develop into either:

Marginal zone B cell (remain in spleen, respond quickly to blood-borne pathogens, follicular B cell (migrate to lymph nodes

and other secondary organs, constantly recirculate)

Resting state B cells can be stimulated to:

Enlarge, develop synthetic machinery, divide, secrete antibody (plasma cells)

B cell activation and response can be:

T-dependent or T-independent