Spread and distribution of Coxiella burnetii in C57BL/6J (H-2b) and Balb/cJ (H-2d) mice after intraperitoneal infection.

Spread and distribution of Coxiella burnetii were investigated immunocytochemically and antigen dissemination was correlated with light microscopic alterations in Balb/cJ (H-2d) and C57BL/6J (H-2b) mice. Intraperitoneal inoculation of C. burnetii resulted in a self-limiting systemic infection. Gross findings consisted of hepatosplenomegaly and histological lesions were characterized by microabscesses and granulomas in numerous organs including spleen, liver, mesentery, bone marrow, lymph nodes, pancreas, heart and uterus. In addition, splenic lymphoid depletion, venous microthrombi and reduction of bone marrow cells were observed. Coxiella burnetii antigen was demonstrated immunocytochemically in the aforementioned organs, especially in spleen, liver and most of all in the bone marrow. Coxiella antigen was detected in macrophages, macrophage precursor cells, and occasionally endothelial cells. Numerous C. burnetii antigen-positive cells were observed between 5 and 12 days post-infection; thereafter, the amount of C. burnetii antigen decreased rapidly. Immunopositivity was detectable until 30 and 44 days post-infection in the bone marrow of Balb/cJ and C57BL/6J mice, respectively. Severity of histological lesions was associated with presence and clearance of C. burnetii antigen. Specific IgM antibodies were detected 4 days after infection and IgG seroconversion was noticed 7 to 10 days post-infection. Coxiella burnetii-specific IgM and IgG antibodies were still present 150 days after infection. Significant strain-specific differences in the antibody response were not found. The findings demonstrate systemic spread of C. burnetii, especially to bone marrow, spleen and liver, and antigen distribution was closely correlated with the appearance and degree of histological lesions.