Sensitization of mice to rickettsial toxin by Coxiella burnetii

Intraperitoneal (ip.) inoculation with live or killed Coxiella burnetii (C.b.) rendered mice more sensitive to intravenous (iv.) administration of a toxic live suspension of Rickettsia typhi. Sensitization of mice by live and killed C.b. was time-and dose-dependent. Killed phase I and phase II C.b. cells possessed a similar degree of sensitization, which was increased slightly by their preincubation with corresponding immune sera. Lipopolysaccharide (LPS)-protein complex extracted from phase I C.b. cells exerted lower sensitization than whole phase I C.b. cells, and chloroform-methanol (CM) treatment of phase I C.b. cells reduced markedly their sensitizing effect. No toxic effect was observed either in C.b.-inoculated or in control mice upon i.v. administration of a heated R. typhi suspension. Specificity of rickettsial toxicity was demonstrated by its distinct reduction both in control and C.b.-inoculated mice after preincubation of R. typhi suspension with immune anti-R. typhi mouse serum.