CD4 and chronic obstructive pulmonary disease: Our novel finding of a pro‐inflammatory effect of UPM on DC‐stimulated CD8 T‐lymphocyte responses, important in the pathology of COPD, is broadly consistent with the literature studying the effect on CD4 T‐lymphocyte responses.16, 17, 18, 19 That such an effect is enhanced with GM‐CSF is in agreement with our current understanding for a pro‐inflammatory role for GM‐CSF in pollution‐induced lung disease.16, 18, 19 Although not the focus of this research, our finding of suppression of MHC class I expression by GM‐CSF is intriguing and deserves more detailed investigation in dedicated studies.