Chlamydia trachomatis pneumonia in the immune, athymic and normal BALB mouse

This paper compares the histopathology of pneumonia due to murine Chlamydia trachomatis (MoPn, mouse pneumonitis agent) in susceptible athymic nude mice (nu/nu), resistant heterozygous littermates (nu/+) and very resistant immunized nu/+ mice. While all groups had an early heterophil response, successful host defence correlated with the presence of large numbers of plasma cells, lymphocytes, monocytes, and lipid laden macrophages. Reticulate bodies were seen in all groups, predominantly in type I alveolar epithelial cells. By 24 h in the immune nu/+ group, no intact organisms were visible. Optimal control of infection was thus rapid and not clearly related to heterophils. These studies show that the histopathology of chlamydial infection may be quite atypical in the immunocompromised host, mononuclear cells seem critical in host defence, and B cell activation with plasma cell infiltration is dependent on intact T cell function in this model.