Differential susceptibility to Mycoplasma pulmonis intranasal infection in X-linked immunodeficient (xid), severe combined immunodeficient (scid), and immunocompetent mice.

Mice with the scid mutation are highly susceptible to Mycoplasma pulmonis infection and develop a disseminated disease. In order to study the contribution of humoral immunity to the immune response, M. pulmonis was inoculated intranasally to X-linked immunodeficient (xid) mice. Severe combined immunodeficient (scid) and immunocompetent CBA mice were used as controls. The mice were killed and necropsied at day 30 or 37 post-infection. Samples from the nose, lungs and joints were taken for bacteriological and histological examination. Rhinitis was observed in all mouse strains. Chronic purulent bronchopneumonia was diagnosed in some of the CBA mice. Xid mice did not show severe lung lesions, despite the presence of numerous mycoplasma organisms in the lungs, in contrast to immunocompetent mice, which developed lung pathology. Scid mice showed less signs of pneumonia, but unlike in xid and CBA mice, there was spread of mycoplasmas from the respiratory tract and severe pathological changes in the joints. Our results indicate that B and/or T lymphocytes protect against dissemination of M. pulmonis from the airways. Innate immune reactions and/or bacterial virulence factors seem to contribute to the development of joint lesions, whereas IgG3 and IgM antibodies might be involved in lung pathology.