Characterization of Immune Responses in Tuberculosis Positive Asian Elephants (Elephas maximus)
Abstract
Tuberculosis is an important health concern for Asian elephant (Elephas maximus) populations worldwide. Most infections are due to Mycobacterium tuberculosis, though mechanisms underlying tuberculosis susceptibility are unknown.3,4 In humans and other species, tuberculosis susceptibility is dependent on the host immune response following infection. Disturbances in the balance between host cell-mediated and humoral immune responses are central to disease pathogenesis.5,7 Recent studies have begun to describe contributions of elephant immune responses to tuberculosis. Real time RT-PCR measurement of cell-mediated (TH1) and humoral (TH2) cytokine levels in baseline peripheral blood samples from tuberculosis positive and negative elephants showed trends towards higher expression of some TH1 cytokines in positive elephants, though findings were not significant.1,2 Subsequent related studies were conducted to examine functional responses of peripheral blood mononuclear cells from 8 tuberculosis positive and 8 negative elephants following mycobacterial antigen stimulation. Results showed that samples from positive elephants exhibited enhanced proliferation and greater production of TH1 cytokines, including tumor necrosis factor-a, interluekin-12, and interferon-g, than tuberculosis negative elephants. Additionally, examination of elephant pulmonary tuberculosis lesions (n=14; 9 affected 5 controls) using light microscopy, immunohistochemistry, and in situ hybridization illustrated distinct patterns of inflammation with morphology and local cytokine expression reminiscent of both human latent and active tuberculosis lesions.6 Altogether, results of these investigations have indicated the elephant immune system does play a role in tuberculosis pathogenesis. Ideally, the foundation of knowledge established by these findings will serve to promote continued investigation of elephant tuberculosis immunopathogenesis for the long-term conservation of this endangered species.
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