HLA-DR antigens and Fc gamma receptors in fetal and infant thymus, examined by a double-marker technique.

HLA-DR antigens and receptors for the Fc part of IgG (Fc gamma R) were examined in cryostat sections and imprints of 12 thymuses from fetuses, infants and children. A double-marker technique, with an anti-T cell serum produced in rabbit and the monoclonal antibody OKIal, was used to study the localization of the thymocytes and the HLA-DR antigens. Membrane-bound HLA-DR antigens were found on about 5% of the thymocytes. A larger proportion of the thymocytes were surrounded by HLA-DR-positive material, probably associated with the thymic epithelial cells. Fc gamma R detected by human aggregated IgG were found on most epithelial cells, but only on a few thymocytes. However, in some areas Fc gamma R were demonstrated on most of the cells stained by the anti-T cell serum. A similar pattern for staining of Fc gamma R was obtained using an anti-Fc gamma R serum produced in rabbit. Fc gamma R were detected on one-third to one-half of the OKT3+ or OKT8+ thymocytes, but only on a few OKT4+ cells. Fc gamma R were present on nearly all the OKT6+ thymocytes at 11 weeks of gestation, whereas in thymuses from older individuals only a few OKT6+ cells had Fc gamma R. The proportions of double-stained cells did not vary much in fetuses older than 14 weeks of gestation, in infants or in children. The results indicate that HLA-DR antigens and Fc gamma R are not correlated to any specific stage of cell maturation.