Solid-phase immunoassays for HCV antibodies in Gamimune N.
OBJECTIVE
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.


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.
Schreiner
C
C
Bayer Corporation, Pharmaceutical Division, Clayton, N.C. 27520, USA.
Musmanno
L
L
Kuenzi
M
M
Torres
J
J
D004396:Coloring Agents; D004797:Enzyme-Linked Immunosorbent Assay; D005189:False Positive Reactions; D018937:Hepatitis C Antibodies / Q000032:analysis* / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000032:analysis* / Q000737:chemistry; D016756:Immunoglobulins, Intravenous / Q000737:chemistry*; D010078:Oxazines; D011487:Protein Conformation; D013696:Temperature
D004396:Coloring Agents; D018937:Hepatitis C Antibodies; D007074:Immunoglobulin G; D016756:Immunoglobulins, Intravenous; D010078:Oxazines; C044808:nile red