Specific vs. nonspecific immune responses in murine respiratory mycoplasmosis.

Murine respiratory mycoplasmosis (MRM), due to Mycoplasma pulmonis, is a chronic respiratory disease in laboratory rats. LEW and F344 rats differ in the severity and progression of disease. LEW rats develop more severe disease than do F344 rats. Also, F344 rats are able to resolve lung and middle ear lesions, but the severity of these lesions in LEW rats continues to increase. LEW lymphocytes produce higher responses in vitro to various mitogens, including M. pulmonis mitogen, than do F344 lymphocytes; this difference is apparently due to higher levels of T-helper cells in LEW rats. The level of infiltration or expansion of mononuclear cells in the submucosa probably depends upon the host's ability to respond to nonspecific stimuli. In contrast to nonspecific responses, F344 rats produce a much higher specific antibody and cellular response to M. pulmonis antigens after immunization, suggesting that F344 rats, in contrast to LEW rats, are able to resolve lesions because they are able to mount an effective immune response to M. pulmonis.