Assessment of oral tolerance induction in graft rejection

Purpose. Oral tolerance has been shown to alter the immune response in some auto-immune diseases, leading to inhibition of immunopathology. We assessed two oral tolerance treatment modalities in an attempt to induce tolerance and reduce cornea graft rejection in an allogeneic rat model. Methods. F344 rats were fed irradiated or non-irradiated splenocytes from ACI rats (50 million per feed). Oral-gastric intubation for both groups was done on days 1, 3, and 5. Animals were sacrificed on day 7. Mixed lymphocyte reactions (MLR) were done with splenocytes from fed and control F344 rats to assess the effect of feeding on the immune responses to ACI and control BN splenocytes. Supernatant obtained from the MLR's was used in CTLL-2 assays for determination of cytokine production. Penetrating keratoplasties were done to compare the rejection responses of fed and unfed F344 rats. Results. Splenocytes from F344 rats fed non-irradiated ACI splenocytes showed a 17% decrease in the MLR compared to controls, while splenocytes from F344 rats fed irradiated ACI cells showed a 93% decrease. Supernatants obtained from the MLR's exhibited inhibition of CTLL-2 growth in both groups. F344 rats fed non-irradiated ACI splenocytes rejected ACI grafts as vigorously as unfed controls. In preliminary tests of F344 rats fed irradiated ACI splenocytes, there was evidence for reduced rejection. Conclusion. To date, we have not been able to induce strong systemic immune inhibition, as assessed by MLR or graft survival, via oral tolerance utilizing non-irradiated splenic derived cells, but have observed better tolerization by feeding irradiated cells.