STAT5A and chronic obstructive pulmonary disease: In addition, exposure to cigarette smoke in the early COPD development leads to a reduction in the signal transducer and activator of transcription 5 (STAT5)+, phospho-STAT5 (pSTAT5)+ cells, and expression levels of anti-inflammatory/immunosuppressive cytokines such as transforming growth factor- β (TGF-β) and interleukin-10 (IL-10), followed by an increase in STAT3+ and pSTAT3+ cells and upregulated IL-17 cytokine [3].