Immunoactive products of human placenta. I. An immunoregulatory factor obtained from explant cultures of human placenta inhibits CTL generation and cytotoxic effector activity.

Supernatants were prepared from short-duration explant cultures of term human placentas obtained after cesarean delivery. These supernatants inhibited murine and human mixed lymphocyte reactions, as well as CTL generation. The effects were reversed by an excess of IL-2-containing medium. Similarly, the material inhibited human natural killer cytotoxicity against K 562 targets. The material was subjected to gel-filtration chromatography on an ACA 44 or Bio-Gel A15m column. The apparent MW of the MLR-CML material was about 60-70 kDa, whereas the NK inhibiting activity was eluted in high-MW components (greater than 200 kDa) as well as in the 50-kDa range. The relevance of this material in local immunoregulation during human pregnancy is discussed.