Aerosol Q fever infection of the nude mouse [Coxiella burnetii]

Athymic nude mice and euthymic littermate controls were exposed to 104 Coxiella burnetii organisms by small-particle aerosol. Antibody response with and without 2-mercaptoethanol treatment of serum was determined at various intervals after infection and serial kills were done to determine morphologic changes in both mouse phenotypes. Total antibody titers determined by the indirect fluorescent antibody technique to phase I and phase II C. burnetii were identical for both groups of mice. Microagglutinin titers determined on days 28 and 33 were abolished by 2-mercaptoethanol treatment of serum from both phenotypes, indicating that the antibody probably resided in the IgM fraction. Microscopically, the reaction to C. burnetii infection was similar in nude and euthymic mice on days 7 and 14. Later, the number and size of lesions attributable to Q fever diminished in euthymic mice. Infection was progressive in nude mice, with macrophage infiltration of most tissues, especially spleen and liver. Numerous rickettsiae were seen by immunofluorescence and electron microscopy in phagocytic vesicles of macrophages, many of which were dilated, giving the macrophage a vacuolated appearance. Results suggest that clearance of C. burnetii infection in mice is dependent upon thymus-derived lymphocytes.