Expression of interferon-γ and its effect on cough hypersensitivity in chronic refractory cough patients

Chronic refractory cough (CRC) is characterised by cough hypersensitivity. Interferon-gamma (IFN-gamma) has been reported to induce calcium influx, action potentials of vagal neurons in vitro and cough response in guinea pigs. While the effect of IFN-gamma in CRC patients remains unknown. Here, via flow-cytometry and inhalation cough challenge, we found CRC patients had significantly increased levels of sputum IFN-gamma(+)CD4(+) T cells, IFN-gamma(+)CD8(+) T cells as well as supernatant of IFN-gamma. The average number of coughs in CRC patients increased as the concentration of inhaled IFN-gamma went up in IFN-gamma cough challenge. Two or more coughs and five or more coughs elicited by inhaled IFN-gamma in CRC patients occurred in 7 of 10 and 2 of 10, respectively. Preinhaled IFN-gamma (100 mu g/mL) increased the capsaicin cough sensitivity in CRC patients but not healthy volunteers. Targeting IFN-gamma may be a potential effective anti-tussive strategy in CRC patients.