File:Janeway-7.5.gif

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Janeway Figure 7.5. The development of a B-lineage cell proceeds through several stages marked by the rearrangement and expression of the immunoglobulin genes. The stem cell has not yet begun to rearrange its immunoglobulin (Ig) gene segments; they are in the germline configuration as found in all nonlymphoid cells. The heavy-chain (H-chain) locus rearranges first. Rearrangement of a D gene segment to a JH gene segment occurs in early pro-B cells, generating late pro-B cells in which VH to DJH rearrangement occurs. A successful VDJH rearrangement leads to the expression of a complete immunoglobulin heavy chain as part of the pre-B-cell receptor, which is found mainly in the cytoplasm and to some degree on the surface of the cell. Once this occurs the cell is stimulated to become a large pre-B cell which actively divides. Large pre-B cells then cease dividing and become small resting pre-B cells, at which point they cease expression of the surrogate light chains and express the μ heavy chain alone in the cytoplasm. When the cells are again small, they reexpress the RAG proteins and start to rearrange the light-chain (L-chain) genes. Upon successfully assembling a light-chain gene, a cell becomes an immature B cell that expresses a complete IgM molecule at the cell surface. Mature B cells produce a δ heavy chain as well as a μ heavy chain, by a mechanism of alternative mRNA splicing, and are marked by the additional appearance of IgD on the cell surface.

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current20:02, 10 March 2004Thumbnail for version as of 20:02, 10 March 2004703 × 278 (27 KB)Tarek (talk | contribs)Janeway Figure 7.5. The development of a B-lineage cell proceeds through several stages marked by the rearrangement and expression of the immunoglobulin genes. The stem cell has not yet begun to rearrange its immunoglobulin (Ig) gene segments; they are i
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