Suppression of natural cell-mediated cytotoxicity in man by maternal and neonatal serum.

the natural cytotoxicity of cells prepared from the blood of human neonates and women at the time of parturition was investigated, using a 4 hr 51Cr release assay and two established cell lines as targets. Although cord cells proved to be cytotoxic, the overall level was distinctly lower than that of normal adult cells. Whereas adult cells from males gave higher levels of cytotoxicity compared with cells from females, this was not the case for cord cells. Cells from women in labour showed even lower cytotoxic values. Neonatal and maternal serum or plasma caused a profound inhibition of the cytotoxicity shown by adult cells when present during the assay or following preincubation of effector cells with serum. Cord cells were not suppressed by either autologous or allogeneic cord sera. The nature of these suppressive factors and their origin and ontogeny remain to be elucidated. It would appear that in the neonate, and possibly also in the fetus, natural cytotoxicity is largely suppressed by serum factors, both in mother and offspring. This could represent yet another example of immunological modulation in pregnancy.