Immunoregulatory effects of human cord blood T lymphocytes on mixed lymphocyte reaction.

Fetuses of outbred mammalian species can survive despite disparities of participants' histocompatibility antigens. During pregnancy, maternal immune response is supposed to be suppressed by various immune suppressive mechanisms. In order to know whether fetal lymphocytes can suppress the maternal immune reaction, we investigated the suppressive effect of human newborns' T lymphocytes. Newborn T cells were isolated from the umbilical cord blood by means of the sheep red blood cell rosette forming method and treated with mitomycin C. The newborn T cells were added as regulator cells to one way mixed lymphocyte reaction (MLR) using maternal lymphocytes, paternal lymphocytes and unrelated donor's lymphocytes. In a control study, adult T cells were treated in the same manner. In any combination of the MLR, the response was substantially suppressed by the addition of cord T cells in comparison with the response by the addition of normal adult T cells. The suppression was dose-related with an increasing number of regulator cord T cells. The suppressive activity of cord T cells showed radiation resistance until 1,000 rads irradiation. In the kinetics study, cord T cells were found to suppress the recognition phase of MLR. These results suggest that cord T lymphocytes suppress the mother's immunological reaction to the fetal antigens.