Microbiome Dependent Regulatory T Cell Generation Correlates with Acute and Chronic Lung Allograft Rejection in a Murine Model

Abstract

Purpose Despite the growing experience in lung transplantation a significant number of patients rapidly succumb to chronic rejection in the form of bronchiolitis obliterans (OB). The reasons for such discrepancies are unknown but have been suspected to relate to individual variability in gut and lung microbiome. Methods To study the role of the microbiome in controlling lung immunology we transplanted C57BL/10 lungs to C57BL/6 recipients from either Jackson Lab, Maine or Envigo facilities in Maryland vs Indiana. Histological grading of acute and chronic rejection, in the form of OB was performed on days 7 and 21 respectively with flow cytometric analysis of the lungs in parallel. Results Recipients from the Maine facility rapidly rejected lung grafts with high ISHLT rejection grades (2.8±0.37) by day 7 while Maryland recipients were rejection-free (0.25±0.25). Delayed histologic evaluation on day 21 post-engraftment revealed evidence of OB in 40% of Indiana recipients while 0% in Maine or Maryland mice(Fig.1A). Flow cytometric analysis revealed a high prevalence of CD4+Foxp3+ Tregs in Maryland recipients (29.56±2.32%) but lower in Maine and Indiana mice while T cell IL-17 levels were also different between them. Systemic different TGF-β levels were also observed. Treatment of Maryland recipients with broad-spectrum antibiotics affected TGF-β levels, decreased the Treg proportion (14.24±1.47%, p Conclusion Our data demonstrate that mice from different origins mount different lung allograft-specific microbiome-related immune responses. Furthermore it suggests that microbiome-dependent TGF beta levels may contribute to the generation of protective Tregs and ameliorate both acute and chronic rejection. Such data puts into question the notion that TGF-β contributes to lung fibrosis and opens up therapeutic avenues of microbiome manipulation to augment the TGF-β -Treg axis.