Evaluation of the level of Mx3 protein synthesis induced by infectious pancreatic necrosis virus (IPNV) strains of different infectivity

The in vitro infectivity and genotype of three IPNV strains (V70, V112 and V98) was linked to the level of transcript synthesis for the Mx3 protein in RTG-2 (Rainbow trout gonad) cells and in Salmo salar. The V70 and V98 strains corresponded to the Sp genotype, whilst the V112 corresponded to VR-299; the presence of Pro-217 and Ala-221 in VP2 identified V70 as a strain of medium virulence level whilst V112 (Ala-217 and Thr-221) and V98 (Pro-217 and Thr-221) were of low virulence. This is concurrent with several in vitro tests which showed V70 to be a strain with highly infectivity (P < 0.05). In both the in vitro and in vivo trials, the strains demonstrated the induction of the Mx transcript, although no differences were detected, and the level always were significantly lesser that observed in poly I:C samples. The results suggest that the infectivity observed is related to the presence of certain specific residues in VP2, and that neither the infectivity nor the genotype appears to bear any relation to Mx induction capacity.