IL17A and chronic obstructive pulmonary disease: In COPD GOLD I, strong positive correlations were revealed between the relative number of circulating Th cells expressing TLR2 and serum levels of IL-6 (r = 0.71 and p < 0.05), IL-17A (r = 0.77 and p < 0.05), and IL-21 (r = 0.79 and p < 0.05).