IDENTIFICATION OF VP3 AS AN IMPORTANT NEUTRALIZING EPITOPE FROM DRT STRAIN, A KOREAN ISOLATE OF INFECTIOUS PANCREATIC NECROSIS VIRUS (IPNV)

Infectious pancreatic necrosis virus (IPNV) has long been known to hav e at least four distinct viral proteins, with the smallest one being a broken piece of VP3. We have previously reported a Korean isolate of IPNV (Park et al., 1989), referred to as DRT, with serotype similar to YR-299. DRT has the typical pattern of viral proteins of IPNV; VP1 (9 6 kDa), VP2 (53 kDa), VP3 (32 kDa), and VP4 (30 kDa). On the basis tha t VP2 is responsible for the determination of different serotypes of I PNV and all different serotypes so far known share the same host speci ficity, it was assumed that there must be an important molecule(s) oth er than VP2 for the infection of host cells. We developed antisera eit her against whole viral particles or against each of the purified vira l proteins, and tested if any antiserum had a neutralising activity du ring the infection. Immunisation with whole viral particles induced ne utralising activity on day 5 after injection, detected by virus neutra lisation assay and ELISA, and the neutralising activity increased abru ptly thereafter. It was found from this antiserum that VP2 was the fir st epitope against which antibody was developed. Antibodies against VP 3/VP4 were detected much later. While the activity against VP2 remaine d constant for at least a month, the amount of antibodies specific to VP3/VP4 increased in proportion to the titre of virus neutralising act ivity. Antiserum against VP2 of DRT, raised in mice, showed extremely low levels of neutralising effect. On the other hand, the mouse antise rum raised against VP3/VP4 had a high level of virus neutralising acti vity. Thus, it appears that VP3/VP4 are major immunogens of IPNV-DRT a nd that these viral polypeptides contain neutralising epitopes. (C) 19 96 Academic Press Limited