Comparative pathogenicity of Mycoplasma bovis and Mycoplasma dispar for the respiratory tract of calves.

Mycoplasma bovis and M. dispar are both important in the etiology of calf respiratory disease, but marked differences are evident in the pathogenesis of disease caused by the two species. Both attach to bovine cells but vary in their invasiveness. M. bovis is capable of invading the lung parenchyma from the airways, while M. dispar predominantly infects the ciliated epithelial cells lining the respiratory tract. M. dispar causes ciliostasis in fetal-bovine tracheal organ cultures, whereas M. bovis does not have the same dramatic effect on ciliary activity. The immunological response of the host contributes to the lesions produced by M. bovis. Both T- and B-lymphocytes accumulate in the lung, which becomes a site for the production of antibody. In contrast, M. dispar produces a mild cellular response in the lungs of calves and may have immunosuppressive properties.