This statistical model implies that, unlike the strongly positive association we have previously described between advanced COPD stage and spontaneous [8] or stimulated [9] production of IFN-γ by lung CD8+ T cells, waning production of IFN-γ by lung CD4+ T cells is significantly associated with spirometrically-defined COPD progression. The gene discussed is IFNG; the disease is chronic obstructive pulmonary disease.