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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.
Vox Sanguinis
|May 22, 1998
Summary
False-positive immunoassay results for immune globulin intravenous (human) (IGIV) are linked to low pH-dependent IgG hydrophobic conformations. Neutralizing pH shifts IgG to a hydrophilic state, reducing false positives in HCV antibody testing.
Area of Science:
- Biochemistry
- Immunology
- Analytical Chemistry
Background:
- Commercially available immunoassay kits occasionally yield false-positive results for Hepatitis C Virus (HCV) antibodies.
- Testing of pH 4 Gamimune N immune globulin intravenous (human) (IGIV) is particularly susceptible to these inaccuracies.
Purpose of the Study:
- To investigate the underlying causes of occasional false-positive immunoassay results for IGIV.
- To identify the conformational properties of IgG that contribute to assay interference.
Main Methods:
- Enzyme immunoassay (EIA) test results were correlated with Nile red hydrophobic dye binding assays.
- IGIV samples underwent pH neutralization and incubation at 37°C for 48 hours to assess conformational changes.
Main Results:
- Reactive EIA results strongly correlated with a higher proportion of low pH-dependent hydrophobic IgG conformations.
- Increased hydrophilic IgG conformations (favored at neutral pH) resulted in nonreactive EIA findings.
- The IGIV preparation procedure significantly reduced false-positive outcomes across four immunoassay formats.
Conclusions:
- The hydrophobic conformation of IgG, prevalent at low pH, is a primary cause of significant nonspecific binding in solid-phase immunoassays.
- Modulating IgG conformation through pH neutralization can mitigate false-positive results in IGIV testing.