Induction of antigraft and antirecipient antibody responses after fully allogeneic and semiallogeneic rat small bowel transplantation

BACKGROUND: Given the potential influence of alloantibodies on organ graft outcome, this study investigated the induction of antigraft and antirecipient antibodies after allogeneic and semiallogeneic rat small bowel transplantation. METHODS: Fully allogeneic, unidirectional rejection and unidirectional graft-versus-host disease (GvHD) heterotopic small bowel transplantation was performed using DA, PVG, and (PVGxDA)F1 donor-recipient combinations. Serum was obtained before and at time points after transplantation and incubated with blood from untransplanted DA and PVG rats. Antibody binding to T cells was detected by whole blood flow cytometry using FITC-conjugated anti-rat IgM murine monoclonal antibody. Antibody levels were determined by reference to a standard curve of fluorescent intensity generated using a serum sample with known anti-target cell IgM activity. Data are presented as arbitrary units/ml (AU/ml). RESULTS: In the PVG-->DA combination, five of six DA recipients had detectable anti-graft (PVG) antibodies by day 4 after transplantation (mean 72 AU/ml) and all animals were positive by day 6 (976 AU/ml). Antirecipient (DA) antibodies were also induced, however, they were only apparent after 6 days in five of eight animals (90 AU/ml). Antigraft (DA) antibody responses were also induced in the DA-->PVG combination (day 6-218 AU/ml), however no antirecipient (PVG) response was apparent. Transplantation induced antirecipient (DA) antibodies in the unidirectional GvHD model (day 6-90 AU/ml) and an anti-graft (PVG) response in the unidirectional rejection model (day 6-60 AU/ml). However, the latter was quantitatively lower than that generated in the PVG-->DA combination (day 6-976 AU/ml). CONCLUSIONS: Antigraft and antirecipient antibody responses are simultaneously induced after fully allogeneic small bowel transplantation, despite rejection being the predominant clinical feature. Further studies are required to elucidate their influence on graft outcome.