P102 Differential antiviral effect of porcine interferon alpha subtypes on classical swine fever virus infection of porcine monocytes
Abstract Introduction Classical swine fever virus (CSFV) causes a serious disease of pigs that is a major threat to pork production industries worldwide [1] . The interferons (IFNs) elicit a variety of antiviral effects and recombinant IFNs have been shown to be prophylactically and therapeutically effective against virus infections [2,3] . Hence we are investigating the potential use of recombinant IFNs as a useful tool in the control of CSFV. We have previously demonstrated that pre-treating monocytes with recombinant porcine (Po) IFN- α subtype 1 and PoIFN- γ resulted in a reduction of CSFV infected monocytes [4] . As there are currently 17 different PoIFN- α subtypes, we investigated whether there are differences in anti-CSFV activity between the subtypes. Methods His-tagged recombinant PoIFN- α 2–PoIFN- α 16 proteins were expressed in Chinese hamster ovary (CHO) cells, affinity purified from culture supernatants and detected by western blot analysis. The activity of the purified proteins was determined with a vesicular stomatitis virus (VSV) bioassay [5] using PK-15 cells and a commercial PoIFN- α 1 as a reference standard. CD14 positive porcine monocytes were pre-treated for 24 h with standardised quantities of recombinant PoIFN- α subtypes, either alone or in combination. Cells were then cultured for a further 24 h in the presence of CSFV and infection was assessed by flow cytometry [4] . Results Pre-treatment of porcine monocytes with PoIFN α -2, 3, 4, 6, 8, 9, 10, 12, 13, 14, 16 and 17 was found to inhibit CSFV infection, with 20 U/ml reducing infection of monocytes to less than 10%, compared to 55% infection in untreated cells. Treatment with poIFN- α 15 reduced the percentage of cells infected, but was significantly less effective than the other 12 active subtypes. In contrast, treatment with poIFN- α 5 and 7 did not result in any notable reduction in the percentage of monocytes infected by CSFV. A combination of PoIFN- α 15 with PoIFN- γ or with PoIFN- α 9 and - β enhanced the antiviral effect of PoIFN α 15 against CSFV. Conclusion Treatment of monocytes with the majority of porcine IFN- α subtypes effectively induced protection against CSFV infection. Interestingly, two subtypes; poIFN- α 5 and 7, had very little anti-CSFV activity, probably due to the virus blocking downstream signalling events of these IFNs. The limited activity of PoIFN- α 15 was shown to be potentiated by combination with other type I or II IFNs. Ongoing studies are investigating which sub-type or subtype combination would be most suited to protection of pigs against CSFV infection.