NITRIC-OXIDE IS PRODUCED BY COWDRIA RUMINANTIUM-INFECTED BOVINE PULMONARY ENDOTHELIAL-CELLS IN-VITRO AND IS STIMULATED BY GAMMA-INTERFERON

Nitric oxide (NO) is a labile inorganic free radical produced by NO sy nthase from the substrate L-arginine in various cells and tissues incl uding endothelial cells. A substantial elevation of nitrite levels ind icative of NO production occurred in cultures of Cowdria ruminantium-i nfected bovine pulmonary endothelial cells (BPEC) incubated in medium alone. Exposure of the infected cultures to recombinant bovine gamma i nterferon (BorIFN-gamma) resulted in more rapid production of NO, redu ced viability of C. ruminantium, and induction of endothelial cell dea th. Significant inhibition of NO production was noted after addition o f the NO synthase inhibitor N-monomethyl-L-arginine (L-NMMA), indicati ng that the increase in production occurred via the inducible NO synth ase pathway. Reduction in the infectivity of C. ruminantium elementary bodies (EBs) occurred in a dose-dependent manner after incubation wit h the NO donor molecule S-nitroso-N-acetyl-DL-penicillamine (SNAP) pri or to infection of endothelial cells, The level of infection in cultur es maintained in SNAP was reduced in a dose-dependent manner with sign ificant negative correlation between the final level of infection on d ay 7 and the level of SNAP (r = -0.96). It was established:that pretre atment and cultivation of C. ruminantium EBs with the NO donor molecul e SNAP reduced infectivity to cultures and viability of EBs with the i mplication that: release of NO in vivo following inflection of endothe lial cells may have an effect upon the multiplication of the agent in the host animal and may be involved in the pathogenesis of heartwater through the effect of this molecule upon circulation.