Positive HLA antibodies are normal and negative HLA antibodies are abnormal. Current research suggests that the mother can produce sensitized T cells during pregnancy that can destroy embryonic cells. If HLA positive, the killing function of sensitized T cells can be inhibited by specific antibodies. If HLA-negative, the sensitized T cells cause miscarriage by acting directly on the embryo or indirectly by damaging the placenta or fetus through the release of inflammatory mediators.HLA-negative patients are usually treated with active immunotherapy with husband’s lymphocytes.