Molecular characterization and expression of Interferon-γ of Asian elephant (Elephas maximus)

Tuberculosis (TB) caused by Mycobacterial organisms has emerged as one of the major diseases in captive elephants. In vitro Interferon-gamma (IFN-γ) assay is being used as an ancillary test for early detection of TB in domestic and captive wild animals. In the present study, basic sequence information and immunological cross-reactivity of this major cytokine of Asian elephants were explored. At predicted amino acid level, IFN-γ of Asian elephant showed maximum identity to that of horse (73%). Other IFN-γ amino acid sequences that showed high level identity were that of giant panda (72%), dog (71%), nine-banded armadillo (69%), cattle (63%) and human (62%). IFN-γ promoter sequences of Asian elephant, human, cattle and mouse showed high level conservation of the putative transcription factor binding sites, TATA box and transcriptional start site. The functionally important human IFN-γ promoter elements, such as AP-2IRE-BE, YY1-γIFN-BED, ATFCS and AP-1γINF binding sites, were absolutely conserved in the corresponding elephant sequence. There was only a single nucleotide variation in the other two important elements, NFAT-γINF and IFN-γPE, indicating the highly conserved regulation of IFN-γ expression across different species. Phylogenetic analysis based on IFN-γ protein sequences revealed a closer relation of Asian elephants and nine-banded armadillo. This shows a closer evolution of these members of Afrotheria and Xenarthra, respectively; and supports the previous reports based on mitochondrial DNA studies. In Western blot analysis, IFN-γ of Asian elephant expressed in Escherichia coli was detected using an anti-bovine IFN-γ monoclonal antibody, indicating immunological cross-reactivity.