IL10 and chronic obstructive pulmonary disease: In the early development of COPD in animal models, exposure to SM decreases the numbers of signal transducer and activator of transcription 5 (STAT5) and phospho-STAT5 (pSTAT5) expressing cells and the expression levels of Treg cytokines transforming growth factor- β (TGF-β) and interleukin-10 (IL-10).