Animal model of Mycoplasma pneumoniae infection using germfree mice.

We have attempted to establish a gnotobiotic mouse model monoassociated with Mycoplasma pneumoniae following single or repeated infection to examine the mechanism of pathogenesis following M. pneumoniae infection. M. pneumoniae inoculated into germfree mice colonized equally well at 10(5) CFU/lung in both single infection and repeated infection. In histopathological observation, repeatedly infected mice showed pneumonia with mild infiltration of mononuclear cells and macrophages. Antibody titers against M. pneumoniae rose in the repeatedly infected mice but not in the singly infected mice. The percentage of CD4-positive, CD8-positive, and CD25-positive lymphocytes infiltrated in the lung was increased in the repeatedly infected mice. In contrast, the lymphocyte subset in the spleen was not significantly different among mock-, singly, and repeatedly infected mice. In the study of cytokine productivity of spleen cells, production of interleukin (IL)-4 and IL-10 was significantly increased and that of gamma interferon was remarkably increased in the mice following repeated infection. These results indicate that a gnotobiotic mouse model monoassociated with M. pneumoniae was established and that immune mechanisms might be involved in the pathogenesis in pneumonia following M. pneumoniae infection.