Distribution of cells bearing the Tac antigen during ontogeny of human lymphoid tissue

The monoclonal antibody anti-Tac, which binds to the interleukin 2 (IL 2) receptor, was used to identify this antigen in human fetal and adult lymphoid tissue. Liver, spleen, thymus, lymph node, and peripheral blood were examined for Tac-positive cells with the use of frozen sections or cytocentrifuge preparations. The results show that cells in the fetal and neonatal thymus express the Tac antigen; these cells are predominantly located in the medulla. The liver and spleen of both fetus and adult exhibit very few Tac-positive cells. Double staining demonstrates that cells bearing the Tac-antigen stain with Leu-4, an anti-T cell antibody. In adult lymph node tissue, the Tac-bearing cells are predominantly distributed in the interfollicular area, with positive cells also present in the germinal center and mantle zone. The Tac antigen is present on both T and B cells. Few Tac-positive cells are present in the circulating peripheral blood.