Single-antibody in situ enzyme immunoassay for infectivity titration of hepatitis A virus.

Hepatitis A virus (HAV) establishes a persistent infection in cultured cells, with minimal effect on host cell metabolism. As a result, the virus produces very little, if any, cytopathic effect (CPE), even with cell culture-adapted strains. This feature precludes the use of a plaque or standard endpoint assay (using CPE as an indicator of infection) for the titration of infectious virus. The radioimmunofocus assay (RIFA) is the standard method for HAV titration, though this method is labour intensive and requires the use of radioisotopes. To this end, a single-antibody in situ enzyme immunoassay (EIA) has been developed, using binding of a perioxidase-labelled monoclonal antibody to fixed cell monolayers as an indicator of infection. This novel assay is highly reproducible, can be read by eye, and is suitable for high throughput situations. Furthermore, the assay has been validated against the RIFA making it suitable for use in studies validating the safety of therapeutic biologicals for human use.