Lack of Effect of Human Chorionic Gonadotropin in Mixed Lymphocyte Reaction in Xenotransplantation

It has been speculated that the immunomodulation associated with pregnancy, e.g., decreasing pro-inflammatory cytokines, increasing anti-inflammatory cytokines, upregulation of T regulatory cells (Tregs), is in part due to the effect of human chorionic gonadotropin (hCG). In this study, we tested the effect of hCG on proliferation of human peripheral blood mononuclear cells (PBMCs) stimulated by irradiated pig PBMCs. Mixed lymphocyte reaction (MLR) was carried out with human PBMCs as responders and irradiated wild-type pig PBMCs as stimulators, with or without hCG. The spontaneous mean proliferation of CD3⁺T cells was 7% and, when stimulated by phytohemagglutinin (PHA) was 43%. When stimulated with irradiated wild-type pig PBMCs, CD3⁺T cell proliferation was 18%. When hCG (at concentrations of 100 IU/ml, 500 IU/ml, and 1,000 IU/ml) was added to the MLR, the proliferation of CD3⁺T lymphocytes was 20%, 20%, and 18%, respectively. hCG also had no effect on the proliferation of CD4⁺T and CD8⁺T cells. hCG does not suppress human lymphocyte proliferation stimulated by wild-type pig PBMCs in MLR (unless this is related to an increased number of Tregs, which was not tested in this study).