Immunology

The susceptibility of the possum to the effects of M. bovis infection has prompted speculation on, and some investigation into the cell mediated immunity of the species.

Artificially infected possums showed no significant hypersensitivity to intradermal tuberculin whereas BCG vaccinated possums did show a slight degree of reaction. The vaccinated possums did show an increased resistance to subsequent infection manifest by longer survival times, fewer and less widely distributed lesions and the development of fewer but larger pulmonary lesions. The latter lesions were large but discrete areas of lung replaced by caseous tissue (O'Hara et al. 1976). These findings suggest that the possum may be a useful model in studying the relationship between hypersensitivity and immunity as the role of hypersensitivity in the immune response of animals to mycobacteria is not completely clear (Salvin and Neta 1975, Youmans 1975).

It has been found that possum splenic leucocytes are less readily induced to transform by low levels of mitogen than are rabbit cells (Moriarty 1973). Lymphocyte transformation is one in vitro method of assessing cell mediated immunity.

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Thus, there is some evidence that cell mediated immunity as a means of controlling tuberculosis is not as well developed in the possum as in other species.