T Cell-Deficiency Exacerbates Diacetyl-Induced Obliterative Bronchiolitis

Purpose RATIONALE: Obliterative bronchiolitis (OB) is the major graft-limiting complication after lung transplantation. OB also occurs in manufacturing workers exposed to compounds such as diacetyl (DA), an artificial butter flavoring. We recently established a novel OB model in rats using intratracheal instillation (ITI) of DA. Given the importance of adaptive immunity in post-transplant OB, we hypothesized that T cells are necessary for the development of DA-induced OB. Methods and Materials Athymic nude rats and wild-type (WT) Sprague Dawley controls received one ITI dose of DA (125mg/kg) and were euthanized 7 days later. Lung OB was semi-quantitatively graded in a blinded fashion. Lung cell suspensions were assessed for RNA transcripts and also analyzed by flow cytometry using antibodies against CD3, CD4, CD25, intracellular FOXP3, and neutrophils. Results Unexpectedly, DA-exposed nude rats had significantly more severe airway obliteration and an increased percentage of airways affected by OB, compared to DA-exposed controls ( Fig. 1 ). A significant reduction in overall T cells and CD4+CD25+FOXP3+ regulatory T cells (Tregs) was confirmed in nude rats vs. WT controls after DA exposure. Lungs of DA-treated nude rats further demonstrated increased neutrophils and upregulation of IL-8, a neutrophil chemoattractant, compared to WT. Conclusions T cell-deficiency leads to exacerbation of DA-induced OB in rats. A potential mechanism may involve decreased regulation by Tregs of IL-8 expression, with a resulting increase in neutrophilic inflammation. Given the limited small animal models that reflect OB pathology, further study of mechanisms that lead to DA-induced OB could be useful to understand basic mechanisms of disease pathogenesis.