PRF1 and chronic obstructive pulmonary disease: A higher percentage of CD28nullCD8+ T cell and NKT-cells expressing perforin and granzyme b was found in COPD patients compared with control subjects (eg., 44 ± 12 (15 ± 13) p = .031; and 34 ± 11 (13 ± 9) p = .021 for the percentage of CD28null CD8+ T cells expressing granzyme b and perforin (median ± sem) from COPD patients (controls) respectively, consistent with a previous report [9].