Ontogeny of ovine lymphocytes. II. An immunohistological study on the development of T lymphocytes in the sheep fetal spleen.

The development of T and B lymphocytes in the ovine fetal spleen was studied immunohistologically using a panel of monoclonal antibodies. A specific sequence of appearance of lymphocyte markers on cells was observed. At 43-44 days of gestation, SBU-T1- and SBU-T8-positive lymphocytes were present in low numbers. However, no SBU-T4, 20.96-, 25.69-, 38.38-, or 46.66-positive lymphocytes were seen until 50-55 days of gestation. Surface immunoglobulin (sIg) was first detected on fetal spleen cells at 45-50 days of gestation. SBU-T19 lymphocytes appeared later in gestation, being observed in fetal spleens at 57 days gestational age (g.a.). The distribution of T cells, B cells and MHC antigens in the developing spleen of the ovine fetus is described.