The migration of lymphocytes in the fetal lamb.

The migration of 51Cr-labeled autologous lymphocytes from intestinal or prescapular lymph was compared in fetal lambs and adult sheep. A subpopulation of lymphocytes present in intestinal lymph of adults which migrated to the small intestine was not found in fetal intestinal lymph. There were marked differences in the migration of fetal and adult lymphocytes to the lungs and liver. In spite of the absence of circulating antibodies or immunoglobulins and of extrinsic antigen in the immunologically virgin sheep fetus, the circulation of lymphocytes through the spleen and lymph nodes of fetal lambs was more intense than in the adult.