Expression of Equine Interleukin-18 by Baculovirus Expression System and Its Biologic Activity

Evaluation of the reactivity of commercially available monoclonal antibodies with equine cytokines

Research on equine cytokines is often performed by analyses of mRNA. For many equine cytokines an analysis on the actual protein level is limited by the availability of antibodies against the targeted cytokines. Generation of new antibodies is ongoing but time consuming. Thus, testing the reactivity of commercially available antibodies for cross-reactivity with equine cytokines is of particular interest. Fifteen monoclonal antibodies against IL-1β, IL-6, IL-8, IL-12, IL-18 and Granulocyte Macrophage Colony stimulating factor (GM-CSF) of different species were evaluated for reactivity with their corresponding equine cytokines. Dot Blot (DB) and Western Blot (WB) analyses were performed using recombinant equine cytokines as positive controls. Immunohistochemistry (IHC) was carried out on equine tissue and flow cytometry on equine PBMC as positive controls. As expected, three equine IL-1β antibodies detected equine IL-1β in DB, WB and IHC. For these, reactivity in IHC has not been described before. One of them was also found to be suitable for intracellular staining of equine PBMC and flow cytometric analysis. Two antibodies raised against ovine GM-CSF cross-reacted with equine GM-CSF in DB, WB and IHC. For these anti-GM-CSF mAbs this is the first experimental description of cross-reactivity with equine GM-CSF (one mAb was predicted to be cross-reactive in WB in the respective data sheet). The other clone additionally proved to be appropriate in flow cytometric analysis. Two mAbs targeting porcine IL-18 cross-reacted in IHC, but did not show specificity in the other applications. No reactivity was shown for the remaining five antibodies in DB, although cross-reactivity of two of the antibodies was described previously. The results obtained in this study can provide beneficial information for choosing of antibodies for immunological tests on equine cytokines.

Expression of recombinant human interferon-γ with antiviral activity in the bi-cistronic baculovirus-insect/larval system

A bi-cistronic baculovirus-insect/larval system containing a polyhedron promoter, an internal ribosome entry site (IRES), and an egfp gene was developed as a cost-effective platform for the production of recombinant human interferon gamma (rhIFN-γ). There was no significant difference between the amounts of rhIFN-γ produced in the baculovirus-infected Spodoptera frugiferda 21 cells grown in serum-free medium and the serum-supplemented medium, while the Trichoplusia ni (T. ni) and Spodoptera exigua (S. exigua) larvae afforded rhIFN-γ amounting to 1.08±0.04 and 9.74±0.35 µg/mg protein respectively. The presence of non-glycosylated and glycosylated rhIFN-γ was confirmed by immunoblot and lectin blot. The immunological activity of purified rhIFN-γ, with 96% purity by Nickel (II)-nitrilotriacetic acid (Ni-NTA) affinity chromatography, was similar to that commercially available. Moreover, the rhIFN-γ protein from T. ni had more potent antiviral activity. These findings suggest that this IRES-based expression system is a simple and inexpensive alternative for large-scale protein production in anti-viral research.

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.

IL-18 Level Correlates with Development of Sepsis in Surgical Patients

Interleukin 18 may play an important role in sepsis. We measured circulating IL-18 levels in 47 patients with surgical wounds, 27 of them had clinical and laboratory evidences of sepsis. The patients had significantly higher IL-18 levels than healthy control (p1 = 0.001), patients with local infection (p4 = 0.001) and patients with clean surgical wound (p5 = 0.001) both at admission and after 48 hours. Serial observations revealed that in all patients, IL-18 levels increased significantly especially in patients with sepsis after 48 h (p = 0.007). IL-18 levels appeared to correlate significantly with leucocytes counts (p = 0.001) and with C-RP (p = 0.007). These results suggest that IL-18 levels are increased in patients with sepsis and correlate with CRP and leukocyte counts suggesting that IL-18 may play a role in sepsis. We suggest that IL-18 could be used as a collaborative evidence of surgical sepsis.

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.