Introduction: Intestinal transplantation (IT) faces many challenges, among them, the necessity to early detect and treat rejection processes. Improving our understanding on the dynamics of allogenic response will be useful to bring candidate targets to these aims. The objective of our study was to determine the kinetics of mucosal T-cells population in the early phase of small bowel rejection using a Heterotopic IT rat model. We made emphasis in phenotypical, activation and exhaustion markers for the early detection of the rejection phenomena.

Methods: Allogeneic heterotopic small bowel IT (n=5) was performed following standard procedure. Brown Norway animals were used as donors and Lewis as recipients. Rats did not receive any immune suppressor treatment. Rejection was monitored by clinical scoring and hematoxylin-eosin staining of intestinal grafts (Gf). T-cells from the peripheral blood (PB) and small bowel mucosa were assessed by flow cytometry. CD3, CD4, CD8, CD25, CD45, CD45RC, PD-1, FoxP3 and anti-Lewis MHC I expression was analyzed. Gf samples were taken at day 0, 3 and 7 post-operative (POD).

Results: No clinical signs of rejection or significant histological changes were observed at day 3. At this time, in PB 7.9 % ± 0,7 of T cells were from the donor, meanwhile in the Gf 42,7% ± 4,6 of T-cells were recipient cells. We observed a significant increase of CD3+CD4+CD25+, CD3+CD4+CD45RC+ and CD3+CD8+CD45RC+ % in comparison with basal levels (PB:p<0,05;Gf:p<0,01). CD3+CD4+CD25+FoxP3+ cells were also increased in the Gf. At day 7 animals present significant weight loss and histological features compatible with mild to moderate cellular rejection. Differently from day 3 POD, in PB we could not detect donor T-cells. In the Gf 70% ± 7 of T-cells were from the recipient. CD3+CD4+CD45RC+ and CD3+CD8+CD45RC+ % were significantly higher than at day 3 POD (PB p<0,001;Gf:p<0,01). We detected increased levels of CD3+CD4+PD-1+ and CD3+CD8+PD-1+ cells in the Gf in comparison to basal levels(p<0,01). No differences in CD25 expression was observed between day 3 and 7.

Conclusion: T-cell replacement in the Gf mucosa is a very fast process and CD25 expression in both PB and the Gf is an early event that precede the histological changes and should be analyzed as a potential biomarker. Considering that T-cells expressing CD45RC have been described as key players in the Gf rejection processes, our results also suggest they could be a relevant target to treat/prevent ACR.