IL13 and chronic obstructive pulmonary disease: Following TCR stimulation, protein levels for the following analytes did not differ between COPD subjects and smokers without COPD, although concentrations (mean ± SD) were low in both groups: IL-10 (57±90 vs. 50±73 pg/mL); IL-13 (47±94 vs. 28±55 pg/mL); IL-17A (undetectable; minimum detectable concentration = 20 pg/mL); TNF-α (13±15 vs. 31±53 pg/mL); CCL5 (431±511 vs. 513±673 pg/mL).