Detection of IgM to hepatitis B core antigen in a reductant containing, chemiluminescence assay

The Abbott PRISM® hepatitis B core (HBc) antigen assay is an automatic in vitro competitive chemiluminescence immunoassay for the detection of total antibody to HBc (anti-HBc) antigen in human serum or plasma. The assay utilizes cysteine solution as a reducing reagent in order to maximize specificity. To help understand the effect of cysteine on detection of anti-HBc antigen, we separated and purified anti-HBc IgM and IgG from human plasma using size exclusion, protein A/G, and affinity chromatography techniques. We showed that cysteine affected the reactivity of anti-HBc IgM with recombinant HBc (rHBc) antigen but not the reactivity of anti-HBc IgG. Anti-HBc IgM treated with cysteine yielded byproducts which were reactive in the PRISM HBcore assay. Reduction-sensitive factor (RSF) — IgM fraction from serum known to be non-specific for anti-HBc activity, similarly treated with cysteine, was no longer reactive in the PRISM HBcore assay. We showed that cysteine treatment is effective against non-specific IgM in human blood. Also, the inclusion of cysteine in the PRISM HBcore assay does not compromise the detection of HBc specific antibodies.