Abstract Rational Interstitial lung disease (ILD) is a chronic fatal pulmonary disorder with poorly understood pathogenesis. Thermal regulation or body temperature regulation is a critical yet understudied variable that modifies immunity. In pre-clinical models, mice housed at an ambient temperature at which they do not expend metabolic energy to maintain core temperature are immunologically unique from mice housed below thermoneutrality, or in cold stress (CS). IL-10 is a critical cytokine in thermal regulation. The role of IL-10 in pulmonary fibrosis is debated. We hypothesized that mice housed at TN are protected from lung fibrosis because of enhanced responses to IL-10 due to regulation of the IL-10 receptor. Methods We use the established model of bleomycin (BLM) induced lung fibrosis to test our hypothesis in C57BL/6L mice exposed to TN (32ºC) or CS (21ºC). Lung injury was assessed by IgM and total protein in bronchoalveolar lavage fluid (BALF) via ELISA and Bicinchoninic Acid assay respectively. Lung collagen content was measured using hydroxyproline assays and histological sections. Single cell RNA (scRNA) sequencing was performed on whole lung single cell suspensions. Flow cytometry was used to identify cell populations and intracellular cytokines. Results We show that bleomycin treated mice housed in TN demonstrate protection against lung fibrosis compared to mice housed at CS. Mice in TN have less weight loss (p ≤ 0.0001, 14 days post BLM), mortality (log rank p = 0.01) and reduced lung collagen content (p ≤ 0.001) compared to CS mice. Initial lung injury, caused by bleomycin administration, is similar in TN and CS conditions (p = 0.99, 5 days post BLM). Transgenic IL-10 deficient mice are not protected in TN conditions with increased lung collagen content (p ≤ 0.01) and mortality (log rank p = 0.02) post bleomycin. IL-10KO mice in TN exhibit an increase in the profibrotic cytokine IL-17(p ≤ 0.0001) and IL-17 producing cell types (p ≤ 0.0001). ScRNAseq revealed an upregulation of Il10ra in inflammatory monocytes and interstitial macrophages in TN mice compared to CS mice treated with BLM (L2FC= 0.84, padj≤ 0.01). In the same cells, Il10ra is downregulated in CS BLM compared to CS saline (L2FC= -1.0, padj≤ 0.0001). Conclusion Thermoneutral exposure may protect against lung fibrosis through modulation of the IL-10 ligand receptor axis whereby protection is dependent on IL-10 presence and upregulation of Il10ra. Our work highlights the importance of environmental conditions in lung fibrosis models and may help discriminate novel molecular pathways involved in the pathogenesis of organ fibrosis. This abstract is funded by: R01HL162659, F31HL181994, Graduate Program in Immunology Miller Fund
Mikhail et al. (Fri,) studied this question.