Reliable confirmation and quantitation of human immunodeficiency virus type 1 antibody using a recombinant‐antigen immunoblot assay

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Abstract
The recombinant DNA-derived, human immunodeficiency virus (HIV) antigen-based immunoblot assay (RIBA-HIV216) is a new supplemental (confirmatory) test developed to detect antibodies to HIV-1. The assay employs four recombinant viral antigens, corresponding to HIV-1 p24, p31, p41 and gp120 proteins, in an immunoblot format. With this assay, HIV-1 antigen reactivity was detected in all 683 infected patient serum or plasma specimens evaluated; 665 (97.6%) of these sera met the criteria for a positive interpretation, and 18 (2.6%) were classified as indeterminate. All 683 samples reacted with the recombinant gp41-equivalent protein. The first sequential enzyme immunoassay (EIA)-reactive samples collected from 33 seroconverting homosexual men reacted on RIBA-HIV216. Eleven (1.1%) of 999 EIA-negative blood donor sera reacted weakly with a single recombinant antigen (p24 or p31), whereas 13 to 48 percent had indeterminate reactions on viral lysate Western blots. One (1.5%) of 66 EIA-positive, Western blot-negative blood donor samples and 19 (29%) of 66 EIA-positive, Western blot-indeterminate blood donor samples scored indeterminate on RIBA-HIV216. Nonspecific reactivity was seen with only 1 (0.8%) of 114 patient sera containing possible interfering antibodies, whereas 33 percent of these samples had indeterminate reactions on Western blot and 35 percent had equivocal reactions on immunofluorescence assay (IFA). We conclude that the RIBA-HIV216 is approximately as sensitive as and significantly more specific than virus-derived Western blot and IFA. The RIBA-HIV216 also allows for semiquantitation of specific antibodies that may be of value in clinical staging and therapeutic monitoring.