Suppression of cellular immune responses in guinea pigs infected with spotted fever group rickettsiae.

Using a guinea pig model, we demonstrated that infections with pathogenic species of spotted fever group rickettsiae transiently and nonspecifically suppress established cellular immune responses as measured by in vitro lymphocyte transformation and in vivo delayed cutaneous hypersensitivity responses to unrelated, nonrickettsial antigens. The correlation of the duration of this immunosuppression with the virulence of the infecting rickettsial species suggests that this suppression is a pathological effect of the rickettsial infection. Although we did not specifically study the mechanism of this suppression, it is not associated with either lymphocytopenia or leukocytosis.