Functional and biochemical properties of a mouse placental immunoregulatory factor

The authors have a long standing interest in immune regulations which control the absence of rejection of a semi-allogeneic fetus by the mother. A previous work described a soluble 40 kDa factor extracted from mouse placenta and capable of inhibiting secondary immune responses in vitro. The present paper reports the following on its mode of action in vivo: (1) it is active even in a fully allogeneic host; (2) it can be administered i.v. or i.p. along with antigen; and (3) the injections of factor and antigen must not be more than 2 days apart for maximum efficacy. Moreover, the results of the study described here indicate also that this factor is a concanavalin A-binding glycoprotein, sensitive to heat and pronase, and different from interleukin 10 (IL-10). Thus, this placental factor appears to be different from previously described immune regulators such as IL-10 and could contribute significantly to immune regulations at the level of the placenta.