Early embryonic histamine-releasing factor: a new model for human implantation.

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.