Immunoregulatory activity in human decidua

The immunoregulatory factor(s) that suppresses normal human peripheral blood mononuclear cells (PBM) function was extracted from the decidua of pregnant women (8-13 weeks). Compared with extracts from the proliferative endometrium, the decidual extracts from fresh surgical specimens markedly inhibited 3H-thymidine incorporation by PBM in response to T-cell mitogens. The majority of the lymphocyte-inhibitory activity was found to be associated with a material of large molecular weight in the decidua, as estimated by Sephadex G-200 filtration. Immunoelectrophoretic analysis followed by Sepharose 4B-anti-human IgG affinity chromatography of the fraction having the inhibitory activity revealed the causative factor to be most likely IgG or a substance copurified with IgG. The results are discussed with respect to a possible role of IgG in a localized non-specific suppressor mechanism in the decidua preventing maternal immunologic attack on the fetal allograft.