The common gamma chain cytokine interleukin‐21 is expressed by activated lymphocytes from two macropod marsupials,Macropus eugenii and Onychogalea fraenata

In mammals, interleukin‐21 is a member of the common gamma chain cytokine family that also includes IL‐2, IL‐4, IL‐7, IL‐9 and IL‐15. IL‐21 has pleiotropic effects on both myeloid and lymphoid immune cells and as a consequence, the biological actions of IL‐21 are broad: regulating both innate and adaptive immune responses and playing a pivotal role in antiviral, inflammatory and antitumour cellular responses. While IL‐21 genes have been characterized in mammals, birds, fish and amphibians, there are no reports for any marsupial species to date. We characterized the expressed IL‐21 gene from immune tissues of two macropod species, the tammar wallaby (Macropus eugenii), a model macropod, and the closely related endangered bridled nailtail wallaby (Onychogalea fraenata). The open reading frame of macropod IL‐21 is 462 nucleotides in length and encodes a 153‐mer putative protein that has 46% identity with human IL‐21. Despite the somewhat low amino acid conservation with other mammals, structural elements and residues essential for IL‐21 conformation and receptor association were conserved in the macropod IL‐21 predicted peptides. The detection of IL‐21 gene expression in T‐cell‐enriched tissues, combined with analysis of the promotor region of the tammar wallaby gene, suggests that macropod IL‐21 is expressed in stimulated T cells but is not readily detected in other cells and tissues. The similarity of gene expression profile and functionally important amino acid residues to eutherian IL‐21 makes it unlikely that the differences in B‐ and T‐cell responses that are reported for some marsupial species are due to a lack of important functional residues or IL‐21 gene expression in this group of mammals.