PRODUCTION OF ALPHA-INTERFERON IN COWDRIA RUMINANTIUM-INFECTED CATTLEAND ITS EFFECT ON INFECTED ENDOTHELIAL-CELL CULTURES

Cattle that resisted experimental heartwater infection caused by the r ickettsia Cowdria ruminantium produced significant levels of circulati ng alpha interferon (IFN-alpha), whereas animals that died from heartw ater did not. In vitro, recombinant bovine IFN-alpha was found to sign ificantly reduce the yield of Cowdria organisms in bovine endothelial cells, but even at a high concentration (1,000 U/ml), IFN-alpha did no t completely prevent the growth of Cowdria organisms in these cells. T his limited inhibitory effect of IFN-alpha is in agreement with the in vivo situation where an infectious process has to take place to induc e a protective immune response. Our results suggest that IFN-alpha pro duced in vivo in response to Cowdria infection may represent an effici ent way to slow down the infection and allow the animal to mount a pro tective immune response. IPN-a is the first endogenously produced fact or shown to have anti-Cowdria activity.