The study describes the effects of crude extracts of the fetal membranes of day 25 sheep conceptuses and of certain purified protein hormones and pregnancy-associated antigen on the mitogen-induced response of sheep peripheral blood lymphocytes (PBL) in vitro. A dose-dependent suppression of the proliferative response of PBL to phytohaemagglutinin, pokeweed mitogen and concanavalin-A was seen when cultures were supplemented with a soluble extract of fetal membranes. Preliminary characterization suggested that the suppressive agent was heat stable and dialysable. These properties distinguished the immunosuppressive component of membrane extracts from ovine pregnancy-associated antigen, which is heat labile and non-dialysable. However, both high and low molecular weight forms of ovine pregnancy associated antigen were also shown to inhibit lymphocyte transformation in vitro. In contrast, ovine luteinizing hormone, prolactin, growth hormone and human placental lactogen were inactive. The findings are consistent with the hypothesis that immunosuppressive substances are present in the gravid uterus during early pregnancy in the sheep.

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PubMedDate not supplied

Direct cytotoxicity mediated by allogeneic and isogeneic pig lymphocytes modified with fluorescein isothiocyanate.

Cell mediated cytotoxicity (CMC) is restricted by the major histocompatibility complex (MHC) in some animal models but not in others. In order to determine if there was MHC restriction in a CMC experimental model, mononuclear cells from blood of two lines of pigs, (1/1) and (6/6) which are homogeneous to the MHC products (SLA-ABCD), were used. Cytotoxic (1/1) cells were induced in vitro and in vivo against (1/1) mononuclear cells modified with fluorescein isothiocyanate (FITC) and tested against (1/1)-FITC isogeneic and (6/6)-FITC allogeneic cells, without showing MHC restriction of the cytotoxicity. The cytolysis was not due to antibody and K cells because fluoresceinated ovalbumin did not inhibit the test. It was not due to the "altered self" reaction against its own MHC products that sometimes may be induced by allogeneic responses, because the (1/1) anti (6/6) cytotoxic cells did not kill haptenated cells (1/1)-FITC. According to the results there was no evidence of MHC restriction of the CMC response of haptenated cells from pigs of (1/1) haplotype.

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