Cloning and sequencing of Indian water buffalo interleukin-18 cDNA

The first evidence of four transcripts from two Interleukin 18 genes in animal and their involvement in immune responses in the largest amphibian Andrias davidianus

Interleukin 18 (IL-18), a member of IL-1 cytokine superfamily, is an important proinflammatory cytokine with multiple functions in both innate immunity and acquired immunity. However, the characteristics and functional roles of IL-18 remain largely unknown in amphibians, which were classed as major group of vertebrates. In the present study, two IL-18 genes (AdIL-18A and AdIL-18B) and four transcripts (AdIL-18A1, AdIL-18A2, AdIL-18B1 and AdIL-18B2) were firstly identified and characterized from Chinese giant salamander (Andrias davidianus). To the best of our knowledge, this is the first report on the presence of more than one gene copy or two transcripts of IL-18 in one species. The complete open reading frames of AdIL-18A1, AdIL-18A2, AdIL-18B1 and AdIL-18B2 were 588 bp, 603 bp, 591 bp and 606 bp, respectively. The putative AdIL-18 proteins possessed the typical IL-1 domains and phylogenetic analysis indicated that AdIL-18s grouped together with other vertebrate IL-18 proteins. The expression profiles of AdIL-18s were investigated under the challenges of Aeromonas hydrophila, Staphylococcus ureae and Poly (I:C) respectively, and the results suggested that AdIL-18s were involved in the immune responses against both bacterial and viral infections. Moreover, the expression levels of two NF-κBs (P100 and P105) and four proinflammatory cytokines (IL-1β, IL-6, TNF-α and IFN-γ) were inhibited in AdIL-18A1/A2-silenced cells when treated with bacteria and viral RNA analog. Additionally, the transcription levels of these immune-related cytokine genes were markedly induced when the lymphocytes were treated with recombinant AdIL-18A1 or AdIL-18A2 proteins, implying the involvement of AdIL-18s in triggering NF-κB signaling and proinflammatory responses. These results might provide new insights into the origin or evolution of IL-18 in amphibians and even in vertebrates.

Expression of bovine (Bos indicus) interleukin-18 in Escherichia coli and its biological activity

IL-18 modulates immune functions by inducing IFN-γ production and promoting Th1 immune responses. In the present study, we amplified and cloned the sequence (582 bp) encoding full-length bovine IL-18 from PBMC stimulated with PHA. The nucleotide and the deduced amino acid sequence of Bos indicus IL-18 showed an identity of 86-98% compared with IL-18 sequences of other ruminants. The insert was subcloned into a pET 32a vector and expressed in Escherichia coli as a fusion protein and the matured protein was obtained by caspase I treatment. The specificity of these proteins was confirmed by western blotting. The biological activity of the purified protein was analyzed by its ability to induce IFN-γ production in PBMC measured by ELISA and qPCR.

Molecular characterization and expression of caprine (Capra hircus) interleukin-18 cDNA

Interleukin 18 (IL-18) has been identified as a potent upstream cytokine required for upregulation of IFN-gamma secretion that plays a crucial role in polarization of Th1 type of immune response. Considering the potential applications of the cytokine in immunomodulation, it has been characterized in many livestock species including cattle, equines, canines, felines and porcines. In this paper we report the isolation, cloning sequencing and expression of caprine precursor IL-18. Full-length caprine IL-18 cDNA was isolated from mitogen-stimulated adherent peripheral blood mononuclear cells using reverse transcription polymerase chain reaction (RT-PCR). The cDNA contained an open reading frame of 579 bp encoding a putative polypeptide of 192 amino acids. Deduced amino acid sequence of caprine IL-18 showed varying amino acid identity with the published sequences of other domestic ruminant species ranging from 94.3% to 96.9%, while it shared over 78% aa identity with other domestic animals. Pairwise multiple aligned sequences showed a deletion of Glu31in caprine IL-18 unlike in other species. Recombinant caprine IL-18 was produced in Escherichia coli, which cross-reacted with two antiporcine IL-18 monoclonal antibodies.