Thymocyte maturation following interaction with thymus-derived macrophages

Murine C57BL/6 thymocytes were cultivated together with syngeneic thymus-derived macrophages (TDMφ) for up to 96 hr to determine whether TDMφ participate in thymocyte maturation. The expression level of H-2^b and Thy-1.2 antigens served as thymocyte differentiation surface markers as analyzed by flow cytometry. Indirect immunofluorescent staining profiles of the thymocytes demonstrate a dramatic increase in H-2^b expression and a profound decrease in Thy-1.2 expression during cultivation with TDMφ. A similar phenomenon was observed when enriched populations of immature thymocytes were cocultivated with TDMφ. These changes were not observed when thymocytes were cultivated alone or with trypsin-treated TDMφ; neither were they observed when cortisone-resistant thymocytes manifesting mature characteristics were cultivated together with TDMφ. These findings suggest that interaction of thymocytes with TDMφ, involving binding and engulfment, results in the appearance of mature thymocyte subsets.