Specificities and sensitivities of three systems for determination of antibodies to human immunodeficiency virus by electrophoretic immunoblotting

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Abstract
Electrophoretic immunoblotting (EIB [Western blotting]) has emerged as the major method for verification of seropositivity for human immunodeficiency virus (HIV) and therefore needs to be thoroughly characterized. The specificities of three EIB systems, our own and two commercial systems, were studied with anticellular sera and serial dilutions of human sera. We demonstrated that in one system, anti-HLA classes I and II gave bands comigrating with viral proteins, which can be controlled by EIB with uninfected H9 cells. In addition, animal antisera, including anti-immunoglobulin enzyme conjugates, occasionally reacted with HIV gag proteins, necessitating appropriate controls. Whereas none of 10 blood donors reacted at the standard dilution in serum (1/100 or 1/400) in any of the three systems, 6, 1, and 2 of 10 donors reacted with p24, p55, or both at a dilution of 1/10 for the three systems tested. Thus, nonspecific reactions can arise in several ways and justify critical EIB interpretation. The sensitivity of the three systems was studied by comparative titrations and direct quantification of bound immunoglobulin G (IgG). In the titrations with all three, the minor anti-HIV bands p53 and p64, coded from pol, were often detectable in higher dilutions than were antibodies to any other HIV protein. The minimum visible amounts of IgG bound per HIV protein band estimated by extra- and interpolation in densitometric curves and liquid scintillation counting of radiolabeled patient IgG were approximately 0.1, 0.05, and 0.02 ng per band in the three systems. One of the commercial systems had both the highest sensitivity and highest specificity.