Identification of HLA-linked antigens by pregnancy-associated non-cytotoxic alloantisera.

Non-cytotoxic sera obtained from post-partum primiparous and multiparous women were examined by a rosette inhibition technique for the presence of antibodies mediating blockade of human B lymphocyte Fc receptors. Selective activity was demonstrated against a panel of normal human B lymphocytes and lymphocytes from patients with chronic lymphocytic leukaemia (CLL). A pattern of specific activity was found in sera and in their IgG fractions, which was not accounted for by antibodies directed to known HLA-A, -B or -DR antigens. Several sera were identified with selective activity in this assay. As the results of testing sera in a direct binding assay correlated with those of the EA inhibition assay, and since EA inhibitory activity occurred in F(ab')2 fractions of sera, it is possible that these non-cytotoxic antibodies bind directly to B cell surface antigens. Sera may therefore have been identified which possess antibodies to hitherto undefined HLA antigens.