For AHSV serotypes 1, 3, 7, 8 and 9, open reading frames based on amino acid sequences of VP2 proteins (GenBank accession number: CAP04841; U01832; AAN74570; ABI96883, respectively), were designed for optimized expression in insect cells

(Gene Art, Regensburg, Germany). VP2 genes were amplified by PCR with specific primers containing BamHI or SmaI site for cloning purposes into the transfer vector pAcYM1 [27]. Recombinant vectors pAcYM1 with VP2 genes were purified and co-transfected into Sf9 cells with linearized baculovirus DNA (strain BAC10:KO1629), using Cellfectin® II Reagent (Invitrogen) according to the manufacturer’s instruction. On day six after transfection, 200 μl of the supernatants were transferred to fresh Sf9 cells in 12-wells plates. After click here the first passage,

supernatants were transferred to fresh Sf9 cells every 3–5 days until virus infection was confirmed by light microscopy. The virus titer was measured by standard plaque assay using Sf21 cells. Recombinant R428 purchase baculoviruses expressing AHSV VP2 were used to infect Sf9 cells with a multiplicity of infection (moi) of 5. Infected cells were incubated at 28 °C for 72 h. Then, infected cells were harvested by centrifugation, washed with phosphate buffered saline (PBS) and pelleted by centrifugation. Cell pellets were suspended in 25 mM sodium bicarbonate (NaHCO3, pH 8.39) at 1.0 × 107 cells/ml. Cells were disrupted by dounce homogenization and after centrifugation at 6000 rpm for 3 min, supernatants containing soluble VP2 protein were collected. To examine the amount of VP2 proteins, soluble VP2 were mixed with equal volumes of SDS-PAGE sample buffer (10 mM Tris-HCl, pH 6.8, 2% (w/v) SDS, 2% β-mercaptoethanol,

20% glycerol, 0.05% bromophenol blue). After heating at 95 °C for 1 min, the samples were analyzed by SDS-PAGE with BSA as concentration standard and protein molecular weight standard (Page Ruler, SM0671, Fermentas). Concentrations of all samples were adjusted to 100 μg of VP2 per ml by 25 mM sodium bicarbonate and stored at −80 ° C until use. All experiments with live animals were performed under the guidelines of the European GBA3 Community (86/609) and were approved by the Committee on the Ethics of Animal Experiments of the Central Veterinary Institute (Permit numbers: 2011-042 and 2011-170). Adult female guinea pigs were purchased from a registered breeding farm for guinea pigs and were randomly divided into groups of six animals. Nine groups were immunized with VP2 protein from each AHSV serotype, two groups were immunized with cocktails of different combinations of VP2 proteins (one consisting of serotypes 1, 3, 7, 8 and other, serotypes of 2, 4, 5, 6, 9, respectively) and one group was immunized with phosphate buffered saline (PBS). Shortly before immunization, recombinant VP2 proteins or PBS in 1.5 ml were warmed to 37 °C and mixed with an equal volume of Montanide 206VG (Seppic) by vortexing.