Eosinophils alleviate lung allograft rejection through their modulation of CD8+ T Cells

Abstract

Abstract Introduction Based on the accumulation of eosinophils (eos) in rejected lung grafts, it was widely held that eos perpetuate lung graft rejection. However, we showed recently in a mechanistic study that eos mediate lung graft tolerance. As eos are also present in rejected lungs, we therefore explore the possibility of a different role of eos in lung graft rejection. Method Using orthotopic left lung transplantation of MHC-1 mismatched Balb/c (H2Kd) donors to C57BL/6J (H2Kb) recipients, with or without co-stimulatory blockade immunosuppression, we quantified the number of eos in lung grafts at day 7 post-transplant (D7). Th1, Th2 and Th17 cytokine profiles of D4 lung grafts were analyzed by quantitative PCR. D7 eos were also analyzed for their expression of Th1, Th2 and Th17 signature genes. The role of eos was examined in iPHIL mice that experience selective ablation of eos after Diphtheria toxin (DT) administration. Balb/c left lungs transplanted into DT or vehicle treated iPHIL mice without immunosuppression were analyzed histologically and flow cytometrically at D4. Results We observed similar numbers of eos, higher Th1 polarization, lower IL33, a Th2 cytokine and less Th17 polarization of the lung microenvironment, and higher expression of the Th1 signature genes among eos, in rejecting compared to accepting lung grafts. Eos deficiency was associated with more rapid lung graft rejection, evidenced in higher CD8+ T cell proliferation, lower CD4/CD8 ratio, and enhanced T cell differentiation to effector memory phenotype. Conclusion Our results indicate that eos directly ameliorate lung graft rejection even in the absence of immunosuppression. This calls for a revalidation of the importance of eos in lung allograft pathology.