The immunological basis of rejection of donor organs by recipients is critical and clinically relevant for the very survival of the allograft and for developing strategies to improve survival of donor organs in a recipient. The immunological event that occurs in a recipient upon receiving a transplant is not a singular event but sequential event encompassing different compartments of the immune system, both cellular and humoral.

In the last century, it was fairly established that antibodies are the primary mediators of both humoral and cellular immune functions and regulation. Professor Paul Ichiro Terasaki, while working as a research fellow with Sir Peter B. Medawar, realized the importance of cellular typing in organ transplantation and, upon his return to the University of California, Los Angeles, established a pioneering tissue typing procedure. In collaboration with transplant surgeon Dr. T.E. Starzl in Denver, Dr. Terasaki proved retrospectively that tissue matching could influence kidney allograft survival and functions.

Since then, immunotechnology relevant to transplantation progressed in the area of tissue typing, with the result that one could recognize multiple arrays of major histocompatibility antigens and the antibodies and subtypes produced by the allograft recipient. Dr. Terasaki realized that antibodies bind to alloantigens on donor organs to bring about their rejection and that some of them are capable of altering cellular immune functions targeting donor organs. Based on various concepts evolved in the 20th century and early 21st century, Dr. Terasaki proposed the Humoral Theory of Transplantation in 2003 in the American Journal of Transplantation.

The purpose of this special issue is to examine current developments concerning the humoral theory of transplantation by inviting original research papers and review articles relating to the theory.

Potential topics include but are not limited to the following:

• Humoral response to MHC antigens and non-MHC biomarkers of transplantation
• Role of antibodies in regulating cellular immune response to organ rejection
• Subclass of antibodies and their receptors involved in organ rejection
• Immunosuppressive strategies and agents to prevent allograft rejection
  • Therapeutic monoclonal antibodies
  • Suppressive mechanisms: antibodies, antigen-antibody complexes, anti-idiotypic antibodies, and specific and nonspecific suppressor cells
  • Antibodies regulating T, B, and NK cells and their relevance to allograft rejection
  • Immunosuppressive drugs to prevent antibody mediated rejection
  • Therapeutic preparations of IVIg-relevance to desensitization and transplantation
  • Blood transfusions: random versus donor-specific blood transfusion
• Humoral theory of transplantation-evidence from animal experiments