RECOMBINANT OVINE INTERFERON-GAMMA INHIBITS THE MULTIPLICATION OF CHLAMYDIA-PSITTACI IN OVINE CELLS

The local production of interferon-gamma (IFN-gamma) in sheep in respo nse to Chlamydia psittaci was measured by cannulation of the efferent lymph duct draining the site of challenge inoculation. Peak production of IFN-gamma (256 U/ml) was detected 24 h after challenge. Based on t hese physiological data, functional studies were carried out in vitro to determine the effect of recombinant ovine (rOv) IFN-gamma on the mu ltiplication of C. psittaci in ovine fibroblasts. IFN-gamma inhibited the multiplication of C. psittaci in ovine cells over a range of conce ntrations (250 U/ml to 2.5 U/ml) in a dose-dependent manner. The inhib ition of chlamydial multiplication was most pronounced when cells were treated with rOvIFN-gamma for 24 h before infection. The addition of exogenous L-tryptophan (500 mu g/ml) to cultures within 48 h of infect ion abrogated the anti-chlamydial effect of rOvIFN-gamma thus suggesti ng that tryptophan deprivation is an anti-chlamydial mechanism induced by rOvIFN-gamma in these ovine cells.