Abstract
During normal pregnancy, the fetus is not rejected by the maternal immune system despite bearing paternal MHC antigen. It has been proposed that this is due to the local production of immunoregulatory factors by the maternal decidua. This study was designed to investigate immunosuppressive factors derived from early human decidua. In the first part of the study, assays were standardised in order to monitor the immunoregulatory activity of factors derived from human decidua. These included mitogen induced lymphocyte proliferation, mixed lymphocyte culture, and the proliferation of human monocytic and T lymphoid cell lines. Using these assays, two fractions from the FPLC separation of the 10-100 KDa crude decidual supernatant with immunosuppressive activity have been identified and partially characterised. One contained molecules of 183 KDa under non-reducing SDS-PAGE analysis, and 70 and 29 KDa under reducing conditions (large molecular weight fraction; LMWF). Another had molecules of 7-14 KDa under non-reducing conditions (small molecular weight fraction; SMWF). Both of them inhibited mitogen-induced lymphoproliferation and the mixed lymphocyte reaction. In addition they inhibited the growth of a monocytic cell line (Mono Mac 6), but not that of a T lymphoblastic cell line (Jurkat E6.1). The suppression of cellular growth by the LMWF, but not the SMWF, was due to the arrest of the cells in the G0/G1 phase of the cell cycle. Neither fraction affected the expression of MHC class II on Mono Mac 6 cells. The decidua-derived suppressive factors showed some similarity to human transforming growth factor type beta (hTGFbeta), but their activity could not be eliminated by neutralising antibodies to hTGFbeta1 and (32. In contrast to the decidua factors, hTGFbeta1 was able to significantly suppress the expression of MHC class II molecules. In addition, acidification of LMWF decreased their suppressive activity, whereas others have shown that similar treatment of TGFbeta isolated from decidua enhanced its activity. Although some similarity to human decidua-associated protein hDP200 could be demonstrated with LMWF, lgG-like molecules could not be demonstrated in the latter. A low molecular weight protein with immunosuppressive activity-PP14- has been demonstrated in human decidua. Despite similarity, the SMWF clearly showed a distinct M.w distribution pattern to PP14 when analysed by Western blot. This suggests that SMWF was not PP14. In the final part of the study, the supernatants of decidual mononuclear cell cultures (non-fractionated or fractionated) were used to investigate the cells which may produce the factors. The preliminary results suggest that non-leukocytic decidua cells are unlikely to be responsible for the activity. Either T lymphocytes or NK cells are the more likely source, as the suppressive activity was largely increased in populations enriched for these cells, and concanavalin A enhanced their suppressive activity. However, the precise cellular source of these factors needs to be elucidated further.