A bursal stromal derived cytokine induces proliferation of MHC class II bearing cells.
To delineate the mechanisms of early embryonic chicken bursapoiesis, we developed several virally transformed stromal cell lines. Extensive phenotyping of one of these lines, BSL.2, with a panel of mAb mapped it as deriving from the E11 bursal surface epithelium. The functional properties of BSL.2 were assessed in vitro by culture of its conditioned medium with either embryonic bursal cells (BC) or adherent cell depleted bone marrow (BM). In both these populations there was an induction of proliferation during the first 72 h of culture, followed by a subsequent loss of proliferative activity coincident with the appearance of phagocytic and non-specific esterase positive adherent cells, which remained viable in culture for up to 3 weeks. Flow cytometric analysis of the proliferating cells demonstrated an increase in the number of MHC Class II+ (B-L+) cells for both BM and BC. There was, however, an overall decrease in total viable cell number during the period of proliferation, demonstrating the stimulation of a specific subpopulation of cells. FACS separation of the unstimulated adherent depleted BM and BC populations demonstrated that only a subpopulation of the B-L+ cells proliferated in response to BSL.2 CM in addition to a subpopulation of B-L-BM. BSL.2 CM stimulated B-L+ BM and BC co-expressed the antigen detected by 68.1, which has been described as a M[symbol: see text] marker, but is also detectable on bursal lymphocytes. In ovo administration, at E11, of concentrated BSL.2 conditioned medium resulted in a significant increase, by E18, of bursal weight and Bu-1 and B-L+ cell number. There were no simultaneous alterations to the spleen. Preliminary MW analysis of the BSL.2 supernatant has revealed an active factor of approximately 90 kDa.
Obranovich
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TD
Department of Pathology and Immunology, Monash Medical School, Prahran, Victoria, Australia.
Boyd
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RL
D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D001853:Bone Marrow / Q000276:immunology*; D002060:Bursa of Fabricius / Q000166:cytology / Q000276:immunology*; D002454:Cell Differentiation; D002460:Cell Line; D002642:Chick Embryo; D017077:Culture Media, Conditioned; D046508:Culture Techniques / Q000379:methods; D016207:Cytokines / Q000302:isolation & purification*; D000949:Histocompatibility Antigens Class II / Q000032:analysis*; D008213:Lymphocyte Activation; D008264:Macrophages / Q000276:immunology; D010641:Phenotype; D017154:Stromal Cells / Q000276:immunology
D017077:Culture Media, Conditioned; D016207:Cytokines; D000949:Histocompatibility Antigens Class II