PRF1 and chronic obstructive pulmonary disease: The mechanisms underlying this resistance, particularly in lymphocytes, are largely unknown [2] Our group has reported increased production of Th1 pro-inflammatory cytokines IFN-γ and TNF-α by CD8+ T cells in peripheral blood and lungs [3] and higher levels of the cytotoxic mediators granzyme b and perforin in peripheral blood in current and ex-smoker COPD patients compared to healthy smokers and never-smokers [4].