Assessment of cellular immune responses of healthy and diseased Tasmanian devils (Sarcophilus harrisii)

The Tasmanian devil (TD) (Sarcophilus harrisii) is under threat from devil facial tumour disease (DFTD), a cancer that is transmitted between devils by direct cell implantation. As no devil is known to have rejected the tumour allograft, an understanding of the immune status of this species is essential to help explain the unique infectious nature of this cancer. We analysed differential white blood cell counts, the phagocytic response of neutrophils as well as mitogen-induced lymphocyte proliferation. Devils analysed included healthy TDs kept in captivity, healthy devils from disease-free and diseased areas as well as diseased devils. Neutrophils isolated from the peripheral blood of healthy devils showed competent phagocytosis and peripheral blood mononuclear cells from healthy and diseased devils proliferated in response to Con A, PHA and PWM stimulation. Although a wide range of responses was observed and relatively high doses of mitogens were required, there was no significant difference between males and females, adults and juveniles or between normal and diseased animals, suggesting that transmission of DFTD is not a consequence of a severely impaired immune system. As lymphocytes from all TDs appear to require strong stimulation for activation, this threshold may contribute to all devils being susceptible to DFTD.