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The relationship between maternal hormones and factors secreted by the implanting embryo is still controversial. We have analysed the in-vitro effect of oestradiol and human embryo-derived histamine-releasing factor (EHRF) on histamine release from rat uterine mast cells. Rat uterine mast cells which were preincubated with oestradiol and then challenged with human EHRF gave histamine release values two- to threefold higher than those without preincubation. The enhancement observed was time- and temperature-dependent. A similar enhancement was obtained with human sensitized basophils but not with rat peritoneal mast cells. Oestradiol, used as a direct challenge, did not induce any histamine release from either rat uterine or peritoneal mast cells, or from human sensitized basophils. Oestradiol preincubation also enhanced the histamine release induced by anti-IgE but did not enhance the histamine release induced by substance P or compound 48/80, two secretagogues that are not mediated by IgE. Moreover, uterine fragments derived from rats at various oestrus phases, with different amounts of endogenous oestrogen, were challenged in vitro with EHRF. The release of histamine by mast cells was higher at the proestrus and preimplantation phases than at dioestrus. All these findings suggest that the interaction of oestradiol with rat uterine mast cells was capable of enhancing in vitro the histamine releasing effect of EHRF. [ABSTRACT FROM AUTHOR]

The interaction between human early pregnancy factor (EPF) and a specific receptor present on human peripheral blood mononuclear cells (PMBC) has been assessed. EPF was radioiodiated by the lactoperoxidase method to a high specific activity, and the [125I]EPF obtained bound in a specific and saturable manner to the receptors on PBMC. Saturation of the binding sites occurred at 10(-9) M. There were 6600 specific binding sites per cell in cells partially purified from pregnant women and fewer in those from non-pregnant women. Unlabelled EPF was capable of competing for binding sites with [125I]EPF, while the binding of [125I]EPF was not inhibited by human chorionic gonadotrophin. A new assay was used that permits the culture of PBMC and the detection of the surface IgG expression in the same microplate. With this method the influence in vitro of human EPF on lymphocyte expression was tested. The results demonstrated a specific inhibition of surface IgG expression of PBMC using a very low concentration of EPF (10 pg/ml). [ABSTRACT FROM AUTHOR]

In this paper are presented preliminary results on the identification of a histamine-releasing factor. This factor was partially purified by means of affinity heparin-Sepharose chromatography from media in which 2-cell human embryos were cultured. The culture was performed in preparation for an in-vitro fertilization (IVF) programme. The mean value of histamine release evoked by the embryo-derived histamine-releasing factor (EHRF) was 56.7%. The release was not due to cytotoxicity since no histamine release was obtained with unsensitized cells and when the assay was performed at 4 degrees C. As a control, no histamine release was obtained using medium from unfertilized oocytes or medium alone. The EHRF could be one of the first signals from the embryo to the uterus. The immunosuppressive activity of histamine is well known, and we suggest that the local secretion of histamine in vivo by uterine mast cells, alone or in cooperation with other factors and/or mechanisms could play a role in preventing maternal immuno-rejection at the implantation stage. [ABSTRACT FROM AUTHOR]