MHC II on transfused murine blood is not required for alloimmunization against MHC I.

Background and Objectives Transfusion of allogeneic platelet products can result in antibodies against donor major histocompatibility complex (MHC) I antigens, leading to a refractory state to subsequent platelet transfusions. However, there is disagreement in the field regarding the molecular mechanisms of humoral alloimmunization. One hypothesis states that donor MHC II is a requirement for alloimmunization. However, other studies have suggested that donor MHC I is alone sufficient and MHC II is not required. Materials and Methods We utilized a mouse model of anti-MHC I alloimmunization to transfused blood, which employed donors with a complete deletion of all MHC II genes. BALB/c (H-2d) recipients were transfused with blood from either C57BL/6 (H-2b) or MHC II null donors on a C57BL/6 background. Anti-MHC I alloimmunization was monitored by indirect immunofluorescence. Results Recipients of either wild type or MHC II null blood produced equivalent humoral responses against donor MHC I antigens. However, there was variation in the relative amounts of IgG subclasses. Conclusion These data reject the hypothesis that donor MHC II expression is required for alloimmunization to MHC I antigens. [ABSTRACT FROM AUTHOR]