IL4 and chronic obstructive pulmonary disease: To deeper investigate whether smoking exposure affected IL-4 in COPD, we analyzed the percentage of IL-4-expressing Th2 cells in subgroups of COPD with either high or low level of IL-4 but all with a low concentration of IFN-γ (IL-4highIFN-γlown = 7, and IL-4lowIFN-γlown = 11) (Fig. 3a).