Identification of alloreactive T-cell epitopes on the Rhesus D protein

Although considerable effort has been devoted to characterizing alloantibod ies specific for the Rhesus D (RhD) blood group antigen, virtually nothing is known about the helper response that drives their production. Therefore, the aim of this study was to map alloreactive T-cell epitopes on the RhD p rotein. Peripheral blood mononuclear cells (PBMCs) were obtained from 22 Rh D-negative volunteers in whom anti-D alloantibodies had developed after del iberate immunization or RhD-incompatible pregnancy, The PBMCs were stimulat ed with a panel of up to 68 overlapping synthetic 15-mer peptides Spanning the complete sequence of the RhD protein. One or more peptides elicited pro liferative responses by PBMCs from all 22 of the alloimmune volunteers but from only 2 of 8 alloantibody-negative control donors. Proliferation of PBM Cs from the alloimmune donors was mediated by major histocompatibility comp lex class II-restricted T cells expressing the CD45RO marker of previous ac tivation or memory. The number of peptides that induced proliferative respo nses was unrelated to either the frequency of, or time since, exposure to R hD-positive red blood cells, but it correlated strongly (R-s = 0.75; P < .0 03) with the level of anti-D antibodies in deliberately immunized donors. T he patterns of stimulatory peptides varied among alloimmune volunteers, but particular sequences were commonly recognized, with 4 peptides each elicit ing a response in more than 50% of these do nors, Identification of such pe ptides containing dominant alloreactive helper epitopes is the first step i n the development of improved or new approaches to preventing hemolytic dis ease of the newborn that are based on modulating the T-cell response to the RhD protein. (C) 2000 by The American Society of Hematology.