Production of a monoclonal antibody against the Snow Mountain agent of gastroenteritis by in vitro immunization of murine spleen cells.

The Snow Mountain agent (SMA) is a 27- to 32-nm noncultivatable virus that causes acute gastroenteritis in humans. SMA is morphologically similar to but immunologically distinct from the Norwalk agent. SMA has been partially purified from the stool of experimentally infected volunteers and contains a single structural protein of Mr 62,000 as well as one or more non-virion-associated soluble proteins. Further characterization of this important human pathogen and other Norwalk-like viruses has been hindered by the lack of reagents with which to study them. To further characterize SMA, we developed a monoclonal antibody to SMA using in vitro immunization--a technique that permitted use of small quantities of antigen for immunization. The monoclonal antibody, SM-4, was specific for SMA and did not react with the Norwalk or Hawaii agents. In addition, SM-4 reacted with purified virion but not with the soluble protein. SM-4 also blocked the ability of labeled postinfection human IgG to bind to purified virion. Finally, both SM-4 and human postinfection sera specifically recognized the Mr 62,000 virion-associated protein. Thus, SM-4 is directed against an epitope present on the SMA structural protein that is not shared by the Norwalk or Hawaii agents and that is not present on the soluble protein. The availability of a monoclonal antibody against SMA should facilitate further purification and characterization of this agent. The techniques utilized in these studies provide a method for the production of additional monoclonal antibodies to this group of viruses and also should be useful for the study of other occult viral agents.