Secretion of a lactosaminoglycan-containing glycoprotein by peri-implantation sheep conceptuses

Properties of human pre- and post-implantation embryo-associated immunosuppressor factor(s)

Embryo-associated immunosuppressor factor (EASF), a factor detected by its suppressive property on the concanavalin A (ConA) stimulated lymphocyte proliferation assay, was purified from human embryo growth media of in vitro fertilized ova (pre-implantation source) and from pregnancy sera (post-implantation source) as 3 fractions, CM-1, CM-3 and CM-6, the immunosuppressive properties of which were studied. The results show that, (i) the 3 fractions of EASF from both sources suppressed ConA- and pokeweed mitogen (PWM)-induced lymphocyte proliferation, suggesting that they have suppressive effects on both T and B cells; (ii) all 3 EASFs were suppressive when added at the early phase of ConA-supplemented cultures; (iii) CM-1 of both sources were suppressive when added to PWM-supplemented cultures between 24 and 48 h; and (iv) CM-6 of both sources showed an irreversible immunosuppressive effect on PWM-induced lymphocyte proliferation, demonstrating that some similarities exist in the immunosuppressive property of EASF from the 2 sources. On the other hand, (i) CM-6 of pre- and post-implantation EASF were immunosuppressive when added to the PWM-supplemented cultures at 24-48 h and 0-16 h, respectively; and (ii) the CM-6 fraction of pregnancy sera, but not the CM-6 fraction of embryo growth media, possessed an irreversible immunosuppressive effect on ConA-supplemented cultures. This active process by which EASF affects T cell and B cell functions directly may be one of several responses by which the maternal immune response against the fetus is prevented.

Inhibition of lymphocyte proliferation by ovine trophoblast protein-1 and a high molecular weight glycoprotein produced by the peri-implantation sheep conceptus

Sheep conceptuses were flushed from uteri on day 16 of pregnancy and cultured in vitro. Three peaks of immunosuppressive activity (i.e., ability to inhibit [3H]thymidine incorporation into mitogen-stimulated lymphocytes) were localized in conceptus-conditioned culture medium: one corresponding to a high-molecular-weight glycoprotein (HMWG; Mr = 800-900 kDa), one corresponding to ovine trophoblast protein-1 (oTP-1), the antiluteolytic, interferon-like molecule of the sheep conceptus, and a third fraction containing a previously undescribed molecule with a molecular weight between 10 and 14 kDa. Both HMWG and oTP-1 inhibited lymphocyte proliferation in a dose-dependent manner. Delaying the addition of HMWG or oTP-1 until 24 h after the addition of phytohemagglutinin (PHA) reduced the degree of suppression relative to cultures where HMWG and oTP-1 were added at the time of PHA addition. Nonetheless, the molecules were still capable of inhibiting proliferation. Addition of human recombinant IL-2 (0-65 U/ml) to PHA-stimulated lymphocyte cultures could not reverse HMWG- or oTP-1-induced suppression of [3H]thymidine uptake by PHA-stimulated cells. Furthermore, treatment of lymphocytes with HMWG or oTP-1 suppressed IL-2-induced proliferation. Therefore, HMWG and oTP-1 affect both early and later events in the in vitro proliferative response of mitogen-stimulated lymphocytes, including responsiveness to IL-2.