Cell mediated immunity in the Australian brushtail possum (Trichosurus vulpecula)

Abstract

The Australian brushtail possum (Trichosurus vulpecula) is very susceptible to infection with bovine tuberculosis suggesting an inability to mount an effective cell-mediated immune response. Experiments were, therefore, designed to evaluate the effectiveness of cell mediated immunity in this species. These included mixed lymphocyte reactions, delayed typed hypersensitivity responses to soluble, particulate and mycobacterial antigens, skin graft rejection and tests of macrophage function. The results of this work indicate that, as in other marsupials, T. vulpecula fails to respond to alloantigens in the mixed lymphocyte reaction. However, and in contrast to earlier studies in marsupials, evidence was produced that T. vulpecula is capable of mounting strong DTH responses compared to a eutherian species, namely the rabbit. Delayed type hypersensitivity responses to a mycobacterial antigen, protein purified derivative, were similar to a Jones-Mote, rather than a classical, type reaction. In other species this finding has been linked with susceptibility to tuberculosis. T. vulpecula also rejects tail skin allografts in a time course comparable to that seen in rats and other eutherians. A method for generating mature, confluent, long-lived T. vulpecula macrophage cultures is described. Lipopolysaccharide did not induce the macrophage cultures to show an enhanced bacteriostatic or bactericidal effect. Histochemical studies on intact tissues indicated a lack of normal levels of the macrophage enzymes β-galactosidase and non specific esterase as compared to the rabbit. The findings in this study, describing delayed type hypersensitivity reactions to mycobacterial antigens and the lack of normal enzyme levels in the macrophage, may help to explain the susceptibility of T. vulpecula to bovine tuberculosis.