Bursal secretory dendritic-like cell: a microenvironment issue.

In 1978, Olah and Glick identified in the medulla of the bursa of Fabricius a dendritic cell, the bursal secretory dendritic-like cell (BSDC). The morphology of BSDC, the functional relationship of BSDC to bursal follicle development and the spleen, and the identification in the embryo of the BSDC precursor was reported. The precursor BSDC appeared in the bursa before B cells. A monoclonal antibody to vimentin, an intermediate filament, will identify BSDC and not B cells in posthatch chickens. The vimentin-positive cells, but not B cells, in hatched chicks express complete IgG chain. Taken together, the present data may contribute to the events occurring during the bursal-dependent stages of B cell development. Immunoglobulin gene rearrangement, within the bursa or at extra-bursal sites, and clonal expansion at extra-bursal sites are antigen-independent and dependent, respectively. The bursal-dependent stage includes the expansion of the Ig rearranged cells and gene conversion, which contributes to antibody diversity. The IgG and granular products produced by BSDC may act as ligand and signals for B cell expansion and gene conversion.