Identification of localized anti-host responses in the graft mesenteric lymph node and Peyer's patches after rat small bowel transplantation.

This study determined the activation status of recipient and donor lymphocyte populations in the graft mesenteric lymph node (MLN) and Peyer's patches (PP) after allogeneic, heterotopic rat small bowel transplantation without immunosuppression. Untransplanted and isografted animals served as controls. The activation status of lymphocyte subsets was determined by flow cytometric evaluation of lymphoblastoid transformation (forward light scatter; FSc). The proportion of activated lymphocytes in the MLN and PP of allografted animals progressively increased. There was also an early transient activation of MLN lymphocytes in isografted animals which probably resulted from surgery-related inflammation. Activated alpha/beta TCR+ and CD4+ cells were detected in the MLN as early as day 3, whereas there was little activation of CD8+ cells. Interestingly, donor lymphocytes became more activated than recipient lymphocytes. Allografting also led to activation of graft-derived PP alpha/beta TCR+ and CD8+ cells, yet there was no detectable activation of recipient-derived lymphocytes. In summary, this study has identified activated donor lymphocytes in the graft MLN and PP after allogeneic small bowel transplantation. Although rejection predominates without immunosuppression, the presence of an underlying anti-recipient response within the small bowel allograft may contribute to graft damage via the localized release of cytokines and inflammatory mediators.