Antigenic characterization of human coronaviruses 229E and OC43 by enzyme-linked immunosorbent assay

Human coronaviruses 229E and OC43 possess three distinct antigens each which are located in peplomer, membrane, and nucleoprotein virion subcomponents. Although specific antigens are associated with similar polypeptides in both viruses, neither shared antigens nor serological cross-reactions have been observed. These findings were confirmed by enzyme-linked immunosorbent assay; rabbit whole-virus-specific antisera reacted with dissociated homologous virus and each of its subcomponents, whereas antisera monospecific to separate subcomponents (peplomers, membrane, or core) recognized only their respective components. Since neither shared antigens nor serological cross-reactions were seen between the two viruses, the specificity of the assay was similar to that of crossed-immunoelectrophoresis, virus neutralization, and complement fixation assays. However, sensitivity was increased at least 1,000-fold; complement fixation antibody titers of 2,000 corresponded to enzyme-linked immunosorbent assay titers of 3,200,000. Similar results were obtained with human convalescent-phase sera. In addition, the most prevalent human antibodies were found to be directed against virion peplomers. However, specific antibodies to core antigens and lesser amounts to membrane antigens were found in the sera of patients, which showed significant antibody rises when purified virion subcomponents were used as antigens. Importantly, rises and declines in titers of antibody to one virus and its specific antigens were independent from levels of titers of antibody to the other virus.