Solid-phase radioimmunoassay for antibodies to flavivirus structural and nonstructural proteins.

A micro-solid-phase radioimmunoassay (SPRIA) is described for quantitation of antibodies to purified flaviviruses as well as to the purified envelope glycoprotein and 80,000-molecular-weight viral nonstructural protein. Sera from mice experimentally infected with Saint Louis encephalitis (SLE) virus or from humans after a primary SLE virus infection reacted more specifically with the major viral envelope protein in the SPRIA test than with antigens conventionally used in the complement fixation (CF) and hemagglutination inhibition tests. A high degree of correlation (P is less than 0.05) was observed between SPRIA anti-immunoglobulin G binding values with the 80,000-molecular-weight nonstructural protein of SLE virus and antibody titers obtained by plaque reduction neutralization and CF with the nonstructural protein. In five of seven human sera in which CF antibody titers to the nonstructural protein were 4 or less, SPRIA testing revealed significant titers of IgG immunoglobulin reactive with this viral protein. The SPRIA test for antibodies reactive with group B togavirus nonstructural protein is as specific and sensitive as the plaque reduction neutralization test for titrating viral antibody in human and animal sera. Antibodies reactive with viral envelope proteins are broadly cross-reactive by the Spria technique, demonstrating both group- and complex-reactive antigenic determinants. The SPRIA test, using wells precoated with antigen, can be completed in 1 day, providing a rapid, highly sensitive test which can be adapted to use in testing a large number of sera.