Dialysis buffer with different ionic strength affects the antigenicity of cultured nervous necrosis virus (NNV) suspensions

Abstract

Nervous necrosis virus (NNV) belongs to the genus Betanodavirus (Nodaviridae). It is highly pathogenic to various marine fishes. Here, we investigated the antigenicity changes of cultured NNV suspensions during 14days of dialyses using a dialysis tube at 1.4×104 molecular weight cut off (MWCO) in three different buffers (Dulbecco’s phosphate buffered saline (D-PBS), 15mM Tris–HCl (pH 8.0), and deionized water (DIW)). Total NNV antigen titers of cultured NNV suspension varied depending on different dialysis buffers. For example, total NNV antigen titer during D-PBS dialysis was increased once but then decreased. During Tris–HCl dialysis, it was relatively stable. During dialysis in DIW, total NNV antigen titer was increased gradually. These antigenicity changes in NNV suspension might be due to changes in the aggregation state of NNV particles and/or coat proteins (CPs). ELISA values of NNV suspension changed due to changing aggregates state of NNV antigens. NNV particles in suspension were aggregated at a certain level. These aggregates were progressive after D-PBS dialysis, but regressive after Tris–HCl dialysis. The purified NNV particles self-aggregated after dialysis in D-PBS or in Tris–HCl containing 600mM NaCl, but not after dialysis in Tris–HCl or DIW. Quantitative analysis is merited to determine NNV antigens in the highly purified NNV particles suspended in buffer at low salt condition.