DEVELOPMENT OF CELL-MEDIATED LYMPHOLYSIS IN HUMAN-FETAL BLOOD-LYMPHOCYTES

Abstract

White cells from pure fetal blood obtained by fetoscopy, or from the cord at birth, were sensitized in mixed lymphocyte culture with irradiated adult peripheral blood lymphocytes. After 6-8 days of culture they were assayed in a standard 4 h 51Cr-release cytotoxicity assay (CML) using lymphoblastoid cell targets from the stimulator cell donor. Fetal age ranged from 15-22 wk of gestation. Third-party target cells and adult blood served as controls. The mean cytotoxic responses of cord (11 donors) and adult (10 donors) blood lymphocytes were not significantly different and had similar kinetics. Fetal lymphocytes (25 donors) displayed a wide range of reactivity with 1/2, scattered throughout the age range, totally negative and a further 23% with marginal responses. Definite cytotoxicity was found in the remainder, but not before the 18th wk; these responses were evenly distributed in the range 18-22 wk. Third-party responses were never more than 1/4 of the specific cytotoxicity. The negative and very weak responses were almost certainly not due to technical factors. Evidently the majority of human fetuses in the age range 15-22 wk, though capable of giving clear mixed lymphocyte reactions, cannot develop full effector function as measured by the CML assay.