Immunosuppressive properties of human placenta: study of supernatants from short-term syncytiotrophoblast cultures.

Using collagenase and mechanical treatment to attempt to eliminate cellular contamination such as macrophages and decidual cells, trophoblast enriched cell suspensions were isolated from the human placenta. With a view to assessing the role of trophoblast in impairing maternal rejection of the fetus, supernatants (SPl4) were prepared from these placental cells after short-term culture (4 h). The immunosuppressive activity of these supernatants was studied following application to mitogen-stimulated human lymphocyte cultures and mixed lymphocyte cultures. In both cases a reproducible inhibition was observed. The ability of these substances to induce a non-specific inhibitory effect was ascertained by observing mouse lymphocyte responses to mitogens or alloantigens. To gain further insight into in vivo fetal protection against anti-paternal cells, we also examined the effects of SPl4 on CTL generation. It was found not only that CTL generation was markedly depressed but also that SPl4 drastically impaired cell-mediated lympholysis at the effector level. To characterize the factors involved in our observations, SPl4 was subjected to dialysis and to chromatography. In the first case, it was found that these factors were not amenable to dialysis. In the second case, we obtained on an Ultrogel AcA 44 column two fractions with immunosuppressive activity. Following our previous work on human syncytiotrophoblast, we analyzed only the low molecular weight inhibitory fraction, which was chromatographed again on Ultrogel AcA 202. The molecular weight of the immunosuppressive factor(s) was estimated to be around 3.5 kDa. We postulate that human trophoblast releases soluble factors around the fetus which may act to protect it against maternal immunological rejection.

Non-specific immunoregulatory factors in the cytosol fraction of human trophoblast.

Cytosol extracts from syncytiotrophoblast of human placenta (HP) have been shown to contain substances capable of suppressing the proliferation of normal human lymphocytes stimulated by mitogens. This suppressive effect has also been observed on lymphocytes stimulated by mitogens and by allogenic cells in various species. The extracts did not, however, inhibit spontaneous (i.e. unstimulated) lymphoproliferation. In addition, HP in some cases exercised an immunostimulatory effect solely on stimulated fractionated lymphocytes. In preliminary experiments the suppressive activity was shown to depend on at least two factors: the first had the ability to bind the mitogen while the second acted irreversibly after 8 h of contact on the lymphocyte itself and was thermostable.

Nonspecific inhibitory activity of soluble human colon carcinoma extracts: tentative mechanism of action.

Soluble human colon carcinoma extract(s) (SCE) were potent nonspecific inhibitors of lymphoproliferative responses to mitogens. Inhibition was concomitant with induction in about 35% of cells of morphologic alterations for most of them comparable with the ones observed in mitogen-induced blast cells. Nonetheless, these blastlike cells did not proliferate. SCE did not interfere with mitogen binding to cell receptors. Moreover, SCE was unable to induce or activate suppressor cells, and its primary target cell was the unresponsive lymphoid cell itself. The inhibitory effect of SCE was early and irreversible. The differential activity of SCE can be correlated with an early [3H]uridine uptake, which was inhibited 6 hours later, as seen for the other biochemical parameters of cell activation. Also, SCE altered membrane-bound ATPase activities. Na,K-ATPase was strongly inhibited, whereas Ca2+-dependent and Mg2+-dependent ATPases were stimulated. These observations were discussed as an SCE-lymphocyte plasma membrane interaction translated into differential signals to the intracellular metabolic pathways.

Nonspecific suppressive and cytostatic activities mediated by human colonic carcinoma tissue or cultured cell extract.

We have previously shown that soluble extracts from human colonic carcinoma (SCE) were potent inhibitors of the PHA-induced DNA synthesis of normal allogeneic peripheral lymphocytes. From the present study, SCE appeared to have a broad and nonspecific range of activity. The SCE-suppressive effect was observed whatever the lymphoid organ or the animal species used as a source of stimulated lymphocytes. Moreover, we always obtained a complete inhibition of the lymphoproliferative response to all tested mitogens including PHA, Con A, PWM, and, for animal lymphocytes, LPS. In addition to the suppressive activity on lymphocytes, SCE also inhibited proliferation of cultured human CCL6 embryonic intestine cells and HT29 colonic carcinoma cells, and of cultured rat fibrosarcoma cells. Soluble extracts from HT29 cells (SCCE) were able to mimic the nonspecific suppressive and cytostatic activities of SCE. The suppressive activity was also found in extracts from hepatic metastases (SHME) of a primary colonic tumor. In contrast, soluble extracts from normal liver or nonmalignant colonic mucosa did not interfere with cell proliferation. These data suggest that both SCE and SCCE contain molecular components(s) that can inhibit a wide variety of proliferating cells, including stimulated lymphocytes.

Inhibition of normal allogenic lymphocyte mitogenesis by a soluble inhibitor extracted from human colonic carcinoma.

Soluble extracts from human colonic tumors (STE) and from their hepatic metastases (SHME) were found to be unable to induce a proliferative response among normal allogenic lymphocytes. However, addition of these tissue extracts to cultures stimulated with various mitogens resulted in an almost complete inhibition of lymphocyte DNA synthesis. Nevertheless, they did not reduce the unstimulated lymphocyte spontaneous proliferation. Control experiments have shown that normal or nonmalignant tissues do not affect the lymphocyte reactivity to mitogens. The specific immunosuppressive evvect was found to be irreversible and to block lymphocyte activation at an early stage. The inhibitor was soluble (not sedimented at 220,000 times G for 2 hr) and not nonspecifically cytotoxic. STE was slso found to induce morphologic alterations resulting in blastlike cell production. However, no mitotic figures were seen, even after colchicin treatment. It is suggested that STE might contain molecular component(s) which would exert a double effect: 1) trigger metabolic alterations responsible for the blast-like cell induction, and 2) inhibit the lymphoproliferative response. The significance of such a mechanism is discussed in conection with the nonspecific immunosuppression caused by a tumor and the immune unresponsiveness against the tumor itself. A preliminiary characterization of this tumor material has shown that its molecular weight was about 70,000 and that it is not related to carcinoembryonic antigen or alpha-fetoprotein.