The part played by cell-mediated immunity in mycoplasma respiratory infections

Intranasal inoculation of M. pulmonis in mice and M. pneumoniae in hamsters results in pneumonia characterised by peribronchiolar and perivascular cuffing by lymphocytes. Thymus-dependent lymphocytes were depleted in mice by thymectomy and X-irradiation or treatment with anti-lymphocyte serum (ALS), and in hamsters by treatment with ALS. These procedures caused a reduction in the severity of pneumonic lesions in infected animals compared with infected immunologically normal animals. In addition, the organisms were present in slightly greater numbers in the lungs of the immunosuppressed animals. These results indicate the importance of thymus-dependent lymphocytes in the pathogenesis of mycoplasma-induced pulmonary disease. However, the role that these cells play in resistance to infection is not known and it may be that local secretory antibody is also important. Results of preliminary experiments involving hamster tracheal organ cultures infected with M. pneumoniae indicate that there is a factor present in lung washings from immune hamsters that protects against loss of ciliary activity brought about by M. pneumoniae.