Fetus as an allograft: noncytotoxic maternal antibodies to HLA-linked paternal antigens.

A cellular enzyme-linked immunospecific assay (CELISA) was used to monitor maternal humoral responses in human pregnancy. Non-cytotoxic IgG antibodies to paternal lymphocytes were detected in sera from 6 of 20 normal first trimester primigravidae and 6 of 13 multiparae. No antibody activity against lymphocytes from their partners was detected in sera from any of the 15 nulliparous women. The differences in antibody response between primigravidae and nulliparae (P = 0.024) and between multiparae and nulliparae (P = 0.005) were statistically significant. Lymphocytotoic antibodies to T- and B-lymphocytes were present in sera from three multiparae, but from none of the women in the other two groups. Family studies indicated that the non-cytotoxic pregnancy-associated maternal antibodies were directed to HLA-linked antigens (P less than 0.001). Evidence obtained using cell panels and platelet absorption suggested, however, that these antibodies were not directed to the currently recognized HLA specificities (HLA-A, -B, -C, or -DR).