Antigenic relationship between human coronavirus strain OC 43 and hemagglutinating encephalomyelitis virus strain 67N of swine: antibody responses in human and animal sera.

Hemagglutinating encephalomyelitis virus of swine (HEV) was adapted to growth in suckling mouse brain. Electron micrographs of HEV-infected suckling mouse brain, prepared by negative staining and thin-section techniques, exhibited typical morphological characteristics shared with other members of the Coronaviridae. The adaptation of HEV to suckling mouse brain facilitated serologic testing by the use of common host reagents and compatible animal systems. With hemagglutination inhibition, complement-fixation, and neutralization tests, an antigenic relationship was demonstrated between human coronavirus OC 43 and HEV in specific immune and hyperimmune animal sera. Children and adults with seroconversion to OC 43 antigen had diagnostic rises in titer of antibody to HEV antigens. Individuals with seroconversion to human coronaviruse 229E and B814 demonstrated antibody to HEV but not diagnostic rises in titer. Swine with titers of antibody to HEV had lower or no detectable titers of antibody to coronavirus OC 43. Although the prevalence and geometric mean titer of antibody to OC 43 were higher than the titer of antibody to HEV in every group of normal humans tested, significant differences in antibody response to coronavirus OC 43 and HEV were seen between populations that did or did not have possible contact with swine. The evidence suggested that antibody to HEV in humans probably represented a heterologous response to infection with coronavirus OC 43. However, a heterotypic response to unknown or uncharacterized strains of coronavirus cannot be excluded.