Immunocytochemical characterization of lymphocyte development in human embryonic and fetal livers.

Lymphohemopoietic progenitor cells and the development of lymphocytes in human embryonic and fetal livers during the 4 to 11 weeks of gestation were examined immunocytochemically by using a panel of monoclonal antibodies. CD9+, CD10+, CD19+, and CD20+ cells of B cell lineage became detectable from the 8th gestational week. CD2+ and CD3+ cells of T cell lineage were observed from the 10th gestational week. Tdt+ cells first appeared on the 43rd day of gestation. Both CD34+ and Ia+ cells were observed in all examined livers, and these cells appeared morphologically as small lymphoid cells from the 43rd day of gestation. These seemed to suggest that B lymphocytes developed in fetal liver from 8 weeks of gestation and lymphohemopoietic progenitor cells were comprised in Tdt+ cells in liver during the 43rd to 56th day of gestation.