Molecular cloning, phylogenetic analysis and expression of beluga whale (Delphinapterus leucas) interleukin 6

Interleukin 6 (IL-6) is a cytokine produced primarily by the monocytes/macrophages with regulatory effects in hematopoiesis, acute phase response, and multiple aspects of the immune response. IL-6 exerts its activity through its binding to specific high affinity receptors at the surface of target cells. As yet, no molecular data have been reported for the beluga whale IL-6. In this study, we cloned and determined the entire beluga whale IL-6-encoding cDNA sequence by reverse transcription-polymerase chain reaction (RT-PCR) sequencing, and analysed its genetic relationship with those from several mammalian species including human, rodent, ruminant, carnivore and other marine species. The identity levels of beluga whale IL-6 nucleic and deduced amino acid sequences with those from these mammalian species ranged from 62.3 to 97.3%, and 42.9 to 95.6%, respectively. Phylogenetic analysis based on amino acid sequences showed that the beluga whale IL-6 was most closely related to that of the killer whale. Thereafter, beluga whale IL-6-encoding sequence was successfully expressed in Escherichia coli by using the pTHIOHisA expression vector for the production of a recombinant fusion protein. The immunogenicity of the recombinant fusion protein was then confirmed as determined by the production of a beluga whale IL-6-specific rabbit antiserum.