Respiratory diseases in cyclophosphamide-treated mice. I. Increased virulence of Mycoplasma pulmonis.

Mice infected intranasally with Mycoplasma pulmonis were treated with cyclophosphamide, a potent immunologic suppressor. In place of a chronic smouldering infection with little mortality (2%), a rapidly lethal infection with high mortality (66%) was produced. M. pulmonis was able to be isolated from several organs during the course of the unmodified infection. In the infected animals treated with cyclophosphamide, dissemination occurred earlier, and higher titers of mycoplasma were found. Reconstitution experiments with spleen cells from previously infected animals reversed the effect of cyclophosphamide, indicating that immunity plays an important role in containment of the infection and eventual recovery.