Immunoregulatory mechanisms in pregnancy. II. Further characterization of suppressor lymphocytes induced by alpha-fetoprotein in lymphoid cell cultures

Nonspecific suppressor cell (SPC) activity has been induced in vitro by preculturing splenocytes from normal mice in the presence of mouse amniotic fluid (MAF) and alpha-fetoprotein for 5 days or more. In adoptive transfer experiments in vivo, these AFP-precultured SPC were shown to reduce the humoral response of mice to sheep red blood cells and the cell-mediated cytotoxic response to allogeneic tumor cells. In mixing experiments in vitro, using freshly explanted splenocytes, the AFP-precultured splenocytes abrogated the generation of specific cytotoxic T-lymphocytes in primary mixed lymphocyte-tumor cell cultures. Supernatants of such precultured cells had at best only a marginal effect. These suppressor cells were found to be nylon-wool nonadherent and their effect could be almost completely abolished by treatment with anti-Thy-1,2 serum plus complement. SPC precursors were found to be sensitive to cyclophosphamide (in vivo) and to hydrocortisone (in vivo and in vitro). At the same time, they are resistant to different doses of radiation.