Development and distribution of HLA-DR antigens and Fc gamma receptors in the human thymus.

HLA-DR antigens and receptors for the Fc part of IgG (Fc gamma R) were studied in cryostat sections of thymus tissue from 24 fetuses, infants and children, using indirect immunofluorescence and indirect immunoperoxidase technique. HLA-DR antigens, detected by a monoclonal antibody (OKIa 1), occurred on the thymic epithelial cells at 11 weeks of gestation, while Fc gamma R, detected by immune complexes and by human heat-aggregated IgG, were present at 10 weeks of gestation. The intensity of the staining for HLA-DR antigens was maximal at about 18 weeks of gestation, while the Fc gamma R activity was maximal at 10-11 weeks. HLA-DR antigens also occurred along the membrane of a few thymocytes, especially in the cortex, while Fc gamma R-activity occurred along the membrane of most of the immature thymocytes. Thymocytes in suspension were examined from children only. Such thymocytes were not stained by OKIa 1, and only 2-6% had detectable Fc gamma R.