Fig. 1

In-vivo immune responses to MHC-mismatched MSCs and corresponding assays. Following injection of MHC-mismatched MSCs in vivo, allogeneic MHC I molecules are directly recognized by alloreactive CD8⁺ T cells, which induces secretion of interferon (IFN)-γ and clonal expansion of cytotoxic T cells. IFN-γ secretion by T cells restimulated with donor allogeneic MHC I molecules can be measured using an ELISPOT. Effector function of cytotoxic T cells specific for donor allogeneic MHC I molecules can be measured using cytotoxicity assays. Allogeneic MHC II molecules are directly recognized by alloreactive CD4⁺ T cells, which induces secretion of IL-4 or IFN-γ and clonal expansion of helper T cells. IL-4 secretion by T cells restimulated with donor allogeneic MHC II molecules can be measured by ELISPOT. Expansion of MHC-specific CD4⁺ T cells can be detected using an ex-vivo MLR. Allogeneic MHC molecules can be shed into the environment where they are processed and presented to lymphocytes by APCs. Following activation by allogeneic MHC peptides, B cells can produce alloantibodies with the support of CD4⁺ T cells activated by indirect allorecognition. Alloantibodies can be detected by ELISPOT or complement-dependent cytotoxicity assays. APC antigen-presenting cell, CDC complement-dependent cytotoxicity, ELISPOT enzyme-linked immunospot, IL-4 interleukin-4, MHC major histocompatibility complex, MLR mixed leukocyte reaction, MSC mesenchymal stem cell