Characterization of capsid genes, expressed in the Baculovirus system, of three new genetically distinct strains of "Norwalk-Like viruses"

"Norwalk-like viruses" (NLVs), members of a newly defined genus of the fami ly Caliciviridae, are the most common agents of outbreaks of gastroenteriti s in the United States. Two features of NLN's have hindered the development of simple methods for detection and determination of serotype: their genet ic diversity and their inability to grow in cell culture. To assess the imm une responses of patients involved in outbreaks of gastroenteritis resultin g from infection with NLN's, we previously used recombinant-expressed capsi d antigens representing four different genetic clusters, but this panel pro ved insufficient for detection of an immune response in many patients. To e xtend and further refine this panel, we expressed in baculovirus the capsid genes of three additional genetically distinct viruses, Burwash Landing vi rus (BLV), White River virus (WRV), and Florida virus. All three expressed proteins assembled into virus-like particles (VLPs) that contained a full-l ength 64-kDa protein, but both the BLV and WRV VLPs also contained a 58-kDa protein that resulted from deletion of 39 amino acids at the amino terminu s. The purified VLPs were used to measure the immune responses in 403 patie nts involved in 37 outbreaks of acute gastroenteritis. A majority of patien ts demonstrated a fourfold rise in the titer of immunoglobulin G to the ant igen homologous to the outbreak strain, but most seroconverted in response to other genetically distinct antigens as well, suggesting no clear pattern of type-specific immune response. Further study of the antigenicity of the NLVs by use of VLPs should allow us to design new detection systems with e ither broader reactivity or better specificity and to define the optimum pa nel of antigens required for routine screening of patient sera.