IFNG and chronic obstructive pulmonary disease: There was however a significant increase in CD137 + Granzyme b + expression in NK cells in COPD patients compared with control subjects (91 ± 8 and 62 ± 14% (mean ± sd) CD137 + GB + NK cells for COPD patients and controls respectively) but not CD137 + IFNγ + NK cells or CD137 + TNFα + NK cells (data not shown).