Effect of nonspecific interactions of the hepatitis B surface antigen with the solid phase on its detection by two-site immunoradiometric assay.

Two-site immunoradiometric assay (Austria II-125, procedure B, Abbott) was used to detect hepatitis B surface antigen (HBsAg) in chronic carrier sera from clinically healthy subjects or from kidney transplant or hemodialysis patients. The titration curves of some high-titered sera showed a prozone-like effect; this corresponded in two such sera LB and MA, to congruent to 80% inhibition of HBsAg detection in undiluted serum relative to a 1:800 dilution. The nature of the inhibition in the above two sera was investigated. We found that the inhibition depended on the time of first incubation but not on the affinity of capture antibodies. Nonspecific adsorption of HBsAg to the solid phase during the first incubation with inhibitory sera and elution of the thus adsorbed antigen during the second incubation, with the resulting neutralization of 125I-labeled anti-HBs, appeared to cause the inhibition of detection observed. The inhibition was prevented by addition of the detergent Triton X-100 to serum or by elution of adsorbed antigen prior to the second incubation, thus indicating that further improvements of the HBsAg immunoradiometric assay may be possible.