Enzyme-immunoassay in the diagnosis of human hepatitis A: specific and non-specific reactions.

Solid-phase enzyme-immunoassay (EIA) used for the detection of hepatitis A virus (HAV) often reveals a non-specific activity which can be reduced or fully eliminated in the presence of normal serum. The factor responsible for this activity appeared to be a non-viral EIA-active material (NVEAM) that non-specifically reacted with normal serum of some mammalian species (human, monkey, rabbit, cattle). The HAV and NVEAM have been separated by CsC1 gradient centrifugation, where the HAV banded in a narrow zone at 1.34 g/cm3, whereas the NVEAM could be found in a wider zone with an average density of 1.31 g/cm3. Non-immunological character of the non-specific activity was demonstrated by the inhibitory effect of weak non-ionic detergents (0.05% Tween 20 or bile, 1:500). The conditions for preferential binding of the HAV by immune sera and elimination of non-specific reaction have been determined.