Respiratory virus-induced dysregulation of T-regulatory cells leads to chronic rejection

Background: Lower respiratory viral infections predispose to bronchiolitis obliterans syndrome (BOS). In addition, there is emerging evidence to support the role of autoimmunity in the pathogenesis of BOS. Because CD4 ⁺CD25⁺Foxp3⁺ regulatory T-cells (Treg) control autoimmunity, we tested the hypothesis that respiratory virus-induced Treg dysfunction leads to BOS. Methods: Treg frequency was monitored using flow cytometry. Apoptosis, cytokines, and antibodies were analyzed using annexin V assay, LUMINEX, and enzyme-linked immunosorbent assay, respectively. Murine studies were performed using the orthotopic tracheal transplant model. Results: (A) Human studies: Treg troughs (decrease >50% of baseline) were found in 13 (43.3%) of 30 lung transplant recipients. Treg isolated during troughs revealed increased apoptosis (37.8%). Patients with Treg troughs had increased prevalence of antibodies to self-antigens collagen type I (23.1% vs 5.8% pretrough), collagen V (7.7% vs 0%), and k-alpha tubulin (30.7% vs 11.7%, p < 0.01) at 6 months post-trough. Increased number of Treg troughs correlated with more rapid onset of BOS. (B) Murine studies: Infection of tracheal transplant recipients with murine parainfleunza sendai virus led to increased Treg apoptosis (50.5%) in the draining lymph nodes. Vaccination against sendai virus prior to transplant abrogated apoptosis of Treg. In vitro, sendai virus-infected, but not naive, tracheal epithelial cells demonstrated upregulation of FasL (>3.5-fold) and induction of co-cultured Treg apoptosis (5.6-fold increase). Conclusions: Respiratory viral infections cause Treg apoptosis which leads to the development of de novo autoimmunity that may play a role in the pathogenesis of BOS.