Specific and non-specific immunosuppressive factors in salamander pregnancy serum

In vitro experiments employing pregnant Salamandra salamandra have previously shown a maternal specific cytotoxic cellular reaction against larval cells and an inhibition of this reaction by maternal serum. Two serum fractions, 19S and 13S, have been implicated in this inhibition. In the present work, the site of action and the identity of the factors responsible for this activity have been determined. Pre-incubation experiments indicate that the 19S fraction from pregnancy serum specifically protects embryonic epithelial cells derived from the same pregnant female. The 13S fraction non-specifically inhibits cytotoxic activity of maternal cells. Both factors implicated in these reactions are respectively an IgM and an alpha 2-macroglobulin. The question of whether the alpha 2M is responsible for immunosuppression is discussed, with particular reference to its vitellogenin analogue and also in view of the fact that the presence of this alpha 2M is not always linked with the immunosuppressive properties (except during pregnancy).