Perforin and granzyme B protein expression by peripheral CD56+, CD3+, CD4+, and CD8+ cells. PBMC were isolated from each subjects. They were first labelled with fluorochrome-conjugated anti-CD56, CD4, CD8, or CD3, permeabilized, then labelled with fluorochrome-conjugated anti- A) granzyme B or B) perforin and analysed by flow cytometry. Columns represent mean ± SEM. Normal non-smokers (white), normal smokers (black), and emphysematous smokers (grey).