D.A. Power

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.

The Fetus as an Allograft: Partial Definition of the Target Antigens

The mechanisms preventing rejection of the semi-allogeneic fetus remain the subject of debate (1). We have recently suggested, however, that Fe receptor-blocking antibodies, detected by the EA rosette inhibition assay, may be important for fetal survival (2, 3). These antibodies, directed to antigens present on B lymphocytes, were found both to be associated with successful pregnancy in humans (2) and to be more common in multiparous (~2Iitters) inbred rats which did not reject renal allografts from the paternal strain (3). In this study we have investigated the target antigens for these antibodies in congenic inbred rat strains, concentrating upon antigens of the RTI region, the major histocompatibility complex of the rat. Materials and methods Inbred rats of the following strains were obtained from commercial sources; Lewis (RTl ) , DA (RTla), PVG (RTI C), PVG.RTl u (RTI U ) and PVG.Rl (RTIA, BC, DC, CC). Sera from multiparous rats were obtained under ether anaesthesia by cardiac puncture 14 days after the second of two litters by the same paternal strain. Alloantibodies were monitored by the EA rosette inhibition (EAI) and indirect haemagglutination (IHA) assays. EAI was performed by a standard technique (3) with nylon wool column enriched B splenocytes; a result of >20 per cent EAI was considered positive. For IHA, a standard haemagglutination assay was performed (3) and the plate washed x 3 prior to the addition of a second antibody (rabbit anti-rat IgG) to develop the plate. The results were expressed as the highest -log, dilution of serum producing visible agglutination. In one part of the study (PVG.RTl u x PVG) F 1 hybrid females were mated with PVG. R 1 (RTI A difference) and PVG (no antigenic disparity) and then transfused intravenously with 0.5 ml DA whole blood 14days after delivery of litters. The alloantibody responses in females mated with PVG. R 1or PVG, together with that in a group of nulliparous females, were assessed by indirect haemagglutination against DA erythrocytes. The Bonferroni test was used to compare differences in IHA titres. Results Lewis anti-DA pregnancy serum (i.e. serum obtained from Lewis females after two pregnancies by DA males) possessed EAI activity against DA strain B lymphocytes in 4/5 animals. In each case, activity was also present in strains possessing the RTI (PVG.RT1) and RTIA (PVG. R 1) antigens of the paternal strain but not against