The role of HHIP in COPD lymphocytic inflammation

Chronic obstructive pulmonary disease (COPD) is characterized by persistent and amplified inflammation to cigarette smoke in vulnerable subjects. The genetic risk of persistent inflammation is poorly understood. A mouse model targeting hedgehog interacting protein (HHIP)(Hhip+--), a genetic risk factor for COPD, displays progressive, persistent inflammation resembling human cases, providing a valuable model to study the contribution of the genetic risk factor HHIP to inflammation in COPD. By single cell RNA sequencing of Hhip+-- lungs at different disease stages, we identified induction of IFN-gamma in activated CD8+T cells possibly driving the inflammatory phenotype in Hhip+-- lungs. Hhip expression was restricted to lung fibroblasts, which interaction with CD8+T cells were mediated by increased levels of IL-18 from Hhip+-- fibroblasts. Our finding provides insight into how a common genetic variation contributes to the amplified lymphocytic inflammation in COPD. single cell RNA sequencing of Hhip+-- and Hhip+-+ mouse lungs at 4 different age points