Antigenic diversity of Norwalk-like viruses: expression of the capsid protein of a genogroup I virus, distantly related to Norwalk virus.

The gene encoding the capsid protein of a genogroup I Norwalk-like virus (NLV) (Hu/NLV/Stav/95/Nor) was cloned and expressed in insect cells using a baculovirus vector. The His-tagged recombinant capsid protein (rStav) was antigenic and immunogenic, showed an apparent molecular weight of approximately 68 kD in protein gels, and was only soluble under denaturing conditions. The amino acid sequence of the rStav protein showed 65-88% similarity to capsid protein sequences from other genogroup I NLV and was most closely related to Desert Shield virus. Norwegian recruit sera were tested for antibodies against rStav by Western blotting (rStav WB). The sera had previously been tested for antibodies against a recombinant Norwalk virus capsid protein in an ELISA (rNV ELISA). Several rNV ELISA-negative sera showed a positive response in the rStav WB, indicating that the use of antigens representing different stains may be necessary when screening sera for antibodies against genogroup I NLV.