Animal Model ofMycoplasma pneumoniaeInfection Using Germfree Mice

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Abstract
We have attempted to establish a gnotobiotic mouse model monoassociated withMycoplasma pneumoniaefollowing single or repeated infection to examine the mechanism of pathogenesis followingM. pneumoniaeinfection.M. pneumoniaeinoculated into germfree mice colonized equally well at 105CFU/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 againstM. pneumoniaerose 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 withM. pneumoniaewas established and that immune mechanisms might be involved in the pathogenesis in pneumonia followingM. pneumoniaeinfection.