The ontogeny of T-cell antigens in the thymus

T-cell-specific antigens were examined in tissue sections of thymus from 24 fetuses, infants, and children. OKT6 monoclonal antibodies faintly stained some thymocytes at 11 weeks of gestation, whereas OKT3, OKT4 and OKT8 did not stain the thymocytes before 14 weeks of gestation. OKT4, OKT6 and OKT8 preferentially stained the cortical thymocytes, in contrast to OKT3, which preferentially stained the medullary thymocytes. The fraction of OKT3- and OKT6-positive cells increased gradually during fetal life. At 24 weeks of gestation about half of the medullary thymocytes were stained by OKT3 and nearly all the cortical thymocytes were stained by OKT6. The fraction of cells stained with OKT4 and OKT8 was maximal at 14-20 weeks of gestation and decreased slightly with increasing age. The preference for either cortex or medulla of cells possessing the various antigens was less pronounced in fetal life than in infancy and childhood. An anti-T-cell antiserum produced in rabbit stained most thymocytes at 10 weeks of gestation. The staining intensity increased gradually until 17 weeks of gestation and then remained constant.