The Spleen Is the Major Source of Antidonor Antibody‐Secreting Cells in Murine Heart Allograft Recipients

Antibody‐mediated allograft rejection is an increasingly recognized problem in clinical transplantation. However, the primary location of donor‐specific alloantibody (DSA)‐producing cells after transplantation have not been identified. The purpose of this study was to test the contribution of allospecific antibody‐secreting cells (ASCs) from different anatomical compartments in a mouse transplantation model. Fully MHC‐mismatched heart allografts were transplanted into three groups of recipients: nonsensitized wild type, alloantigen‐sensitized wild‐type and CCR5^?/? mice that have exaggerated alloantibody responses. We found that previous sensitization to donor alloantigens resulted in the development of antidonor alloantibody (alloAb) with accelerated kinetics. Nevertheless, the numbers of alloantibody‐secreting cells and the serum titers of antidonor IgG alloantibody were equivalent in sensitized and nonsensitized recipients 6 weeks after transplantation. Regardless of recipient sensitization status, the spleen contained higher numbers of donor‐reactive ASCs than bone marrow at days 7 – 21 after transplantation. Furthermore, individual spleen ASCs produced more antidonor IgG alloantibody than bone marrow ASCs. Taken together, our results indicate that the spleen rather than bone marrow is the major source of donor‐reactive alloAb early after transplantation in both sensitized and nonsensitized recipients.