Comparison of systemic cytokine levels in mycobacterium spp. seropositive and seronegative Asian elephants (Elephas maximus)

Mycobacterium spp. infection is an important health concern for Asian elephant (Elephas maximus) populations worldwide. The disease is of particular concern considering its potential to affect not only the individual animal but also herd and public health. Although elephant tuberculosis susceptibility is poorly understood, immune function alterations are central to disease pathogenesis in other species and probably affect outcome of mycobacterial infections in elephants. Measurement of immune mediator (cytokine) levels within blood samples can provide information regarding immune function that may elucidate disease susceptibility. For this study, mRNA levels of interleukin (IL)-2, IL-4, IL-10, and IL-12; interferon (IFN)-γ; tumor necrosis factor (TNF)-α; and transforming growth factor (TGF)-β were measured using elephant-specific, real-time reverse transcription-polymerase chain reaction (RT-PCR) assays in RNA-preserved whole blood samples from 106 Asian elephants, 15 of which were Mycobacterium tuberculosis complex seropositive. The Elephant TB STAT-PAK® (Chembio Diagnostics, Inc., Medford, New York 11763, USA), a novel lateral flow antibody detection assay developed for specific use in elephants, was used to determine serologic status for the study. Seropositive animals had higher levels of TNF-α and lower levels of TGF-β than seronegative animals; these differences between groups were statistically significant when levels were analyzed as categorical variables. Trends toward higher levels of IFN-γ and IL-4 and slightly lower levels of IL-10 and IL-12 were noted in the seropositive group, although differences between groups were not statistically significant. Presence of other inflammatory conditions was found to be a significant confounding variable in the analysis of the relationship between tuberculosis status and TNF-α levels, necessitating its inclusion in statistical models. Age and sex were not found to significantly affect the relationship between tuberculosis status and any of the cytokines measured. Interleukin-2 levels were below the sensitivity of the real-time RT-PCR assay irrespective of tuberculosis status. These findings provide a foundation for future research into the immunopathogenesis of elephant tuberculosis.