Specifically in COPD small airways, IL-17 receptor C (IL17RC) and CXCL1 (upstream and downstream components of the IL-17 F inflammatory pathway, respectively) were both identified to be hypermethylated and underexpressed, while DNA hypomethylation and overexpression of colony stimulating factor 2 (CSF2), an IL-17 F-induced pro-inflammatory cytokine, was observed [89]. Here, IL17A is linked to chronic obstructive pulmonary disease.