The effect of anti-D immunoglobulin administration on plasma cytokine profiles.

Haemolytic disease of the fetus and newborn (HDFN) is, without preventive action, a common cause of fetal morbidity and mortality. The condition is caused by maternal antibody to red cell antigens crossing the placenta and mediating the destruction of fetal red cells. This results in fetal anaemia, jaundice, and in severe cases, death. In western populations the commonest causative antibody is anti-D. For forty years the incidence of alloimmunisation to the RhD antigen, and hence HDFN, has been moderated by the administration of anti-D immunoglobulin to RhD- mothers. The treatment is extremely effective but the mechanism of action remains unresolved.The aim of this quasi-experimental study is to test the hypothesis that there is a significant difference in maternal plasma cytokine expression before and after anti-D administration, thereby increasing the understanding of the mechanism of action. To recruit a participant cohort, RhD- women called to anti-D prophylaxis clinics at 28 weeks gestation were sent a leaflet describing the study 3-6 weeks before their appointment, and invited to participate. Blood samples were collected from 24 women receiving anti-D at 28 weeks gestation, before, and at 1, and 24 hours after administration. The concentration of plasma cytokines was measured by flow cytometry, and/or by enzyme linked immunosorbant assay (ELISA). Participants were allocated to test and control groups by the RhD group of their babies, determined at delivery. Changes in cytokine concentration greater than 50% (1.5 fold) were detected by ELISA for IL-1 ra and TGF-beta1. mRNA of white blood cells of these two cytokines was measured by quantitative polymerase chain reaction. When combined, the difference in TGF-beta1 responses in RhD+ and RhD- fetus arms were found to be statistically significant (p=0.047). When ELISA and PCR results were considered separately, no significant difference was noted in fold changes in test and control groups (p>0.05). TGF-beta1 is a powerful immunosuppressant acting on the key cellular elements of the humoral immune response. The results of this study suggest that the mechanism by which anti-D prevents alloimmunisation includes the induction of TGF-?i secretion. Monoclonal anti-D selected for trials to replace human products have focussed on antibodies capable of causing clearance of fetal red cells from the maternal circulation, and have to date had poor results. The knowledge that anti-D prophylaxis has additional biological effects which may contribute to immunosuppression should inform the selection of monoclonal antibodies for future trials.