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Solid-phase immunoassays for HCV antibodies in Gamimune N
C Schreiner1, L Musmanno, M Kuenzi
1Bayer Corporation, Pharmaceutical Division, Clayton, N.C. 27520, USA.
Background And Objectives:
Occasional false-positive results for the presence of HCV antibodies occur when testing pH 4 Gamimune N immune globulin intravenous (human) (IGIV) using commercially available immunoassay kits. We investigated the causes.
Materials And Methods:
EIA test results were compared with Nile red hydrophobic dye binding.
Results:
There was a strict correlation of reactive EIA results with a larger relative proportion of molecules in a low pH-dependent hydrophobic conformation. Conversely, the greater the hydrophilic contribution to the population of IgG molecules (favored at neutral pH), the more nonreactive the EIA test results became for the same lots. An IGIV test preparation procedure consisting of pH neutralization followed by 48-hour incubation at 37 degrees C decreased positive test result outcomes in four different immunoassay formats by shifting the IgG population to a more hydrophilic conformation.
Conclusions:
The hydrophobic conformation of IgG favored at low pH appears to give rise to significant levels of nonspecific binding in solid phase immunoassays.