In this report we describe the topological mapping of neutralizing domains of canine parvovirus (CPV). We obtained 11 CPV-specific monoclonal antibodies (MAbs), six of which are neutralizing. The reactivities were as determined by ELISA and Western blot (immunoblot) analysis. VP2, the most abundant protein of the CPV capsid, seemed to contain all the neutralization sites. Also, an almost full-length genomic clone of CPV was constructed in the bacterial plasmid pUC18 to enable expression of CPV proteins. All the neutralizing MAbs recognized recombinant VP2 when it was expressed as a free protein in Escherichia coli but not when expressed as a fusion protein with glutathione-S-transferase. When two large fragments containing about 85 % and 67 % of the C terminus of VP2 were expressed, no neutralization sites were detected. When fusion proteins containing the N terminus were expressed, two linear determinants were mapped, one between residues 1 to 10 of VP2, and the other between amino acids 11 and 23. The peptide 11 GQPAVRNERATGS 23, recognized by MAb 3C9, was synthesized chemically and checked for immunogenicity, not being able to induce neutralizing activity. Although the antibody response in rabbits to all the fusion proteins was uniformly high, the anti-CPV response was very variable. Protein from pCPVExl 1, which contains a T cell epitope (peptide PKIFINLAKKKKAG) present in the VPl-specific region as well as the B cell epitopes, seemed to be the most effective in inducing virus neutralization.

SUMMARYWe have determined the nucleotide sequence of an almost full-length clone of porcine parvovirus (PPV). The sequence is 4973 nucleotides (nt) long. The 3' end of virion DNA shows a Y-shaped configuration homologous to rodent parvoviruses. The 5' end of virion DNA shows a repetition of 127 nt at the carboxy terminus of the capsid proteins. The overall organization of the PPV genome is similar to those of other autonomous parvoviruses. There are two large open reading frames (ORFs) that almost entirely cover the genome, both located in the same frame of the complementary strand. The left ORF encodes the non-structural protein NS1 and the right ORF encodes the capsid proteins (VP1, VP2 and VP3). Promoter analysis, location of splicing sites and putative amino acid sequences for the viral proteins show a high homology of PPV with feline panleukopenia virus and canine parvoviruses (FPV and CPV) and rodent parvovirus. Therefore we conclude that PPV is related to the Kilham rat virus (KRV) group of autonomous parvoviruses formed by KRV, minute virus of mice, Lu III, H-I, FPV and CPV.

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A new commercially available antigen-capture, blocking enzyme-linked immunosorbent assay (antigen-capture b-ELISA), based on baculovirus truncated-S recombinant protein of Transmissible gastroenteritis virus (TGEV) and 3 specific monoclonal antibodies, was developed and evaluated by examining a panel of 453 positive Porcine respiratory coronavirus (PRCoV), 31 positive TGEV, and 126 negative field sera by using another commercially available differential coronavirus b-ELISA as the reference technique to differentiate TGEV- from PRCoV-induced antibodies. The recombinant S protein-based ELISA appeared to be 100% sensitive for TGEV and PRCoV detection and highly specific for TGEV and PRCoV detection (100% and 92.06%, respectively), when qualitative results (positive or negative) were compared with those of the reference technique. In variability experiments, the ELISA gave consistent results when the same serum was evaluated on different wells and different plates. These results indicated that truncated recombinant S protein is a suitable alternative to the complete virus as antigen in ELISA assays. The use of recombinant S protein as antigen offers great advantages because it is an easy-to-produce, easy-to-standardize, noninfectious antigen that does not require further purification or concentration. Those advantages represent an important improvement for antigen preparation, in comparison with other assays in which an inactivated virus from mammalian cell cultures is used.