Production of tumour necrosis factor-alpha (TNF-alpha) and reactive nitrogen intermediates by ovine peripheral blood leucocytes stimulated by Ehrlichia (Cytoecetes) phagocytophila.

Ehrlichia (Cytoecetes) phagocytophila, the causative agent of tick-borne fever in sheep and pasture fever in cattle, is an immunosuppressive, obligately intracellular rickettsia that invades granulocytes and monocytes of ruminants. Infected animals are known to suffer from a number of secondary infections. The mechanisms of immunosuppression are believed to be associated with physical or functional damage to leucocytes and the release of immunosuppressive substances. In the present study, the effects of E. phagocytophila on the production of tumour necrosis factor-alpha (TNF-alpha) and reactive nitrogen intermediates by ovine peripheral blood mononuclear cells (PBMCs) were investigated in vivo and in vitro. The concentration of TNF-alpha and nitrate in ovine sera were significantly increased during infection with E. phagocytophila, peak concentrations occurring at the peak period of rickettsiaemia. The addition of E. phagocytophila to cell cultures enhanced in-vitro production of TNF-alpha and nitric oxide by normal ovine PBMCs.