Earlier detection of human immunodeficiency virus type 1 p24 antigen and immunoglobulin G and M antibodies to p17 antigen in seroconversion serum panels by immune complex transfer enzyme immunoassays

For earlier diagnosis of human immunodeficiency virus type 1 (HIV-1) infection, the sensitivities of immune complex transfer enzyme immunoassays for HIV-1 p24 antigen and antibody immunoglobulin G (IgG) to HIV-1 p17 antigen were improved approximately 25- and 90-fold, respectively, over those of the previous immunoassays by performing solid-phase immunoreactions with shaking and increasing the serum sample volumes, and immune complex transfer enzyme immunoassay of antibody IgM to p17 antigen was also performed in the same way as the improved immunoassay of antibody IgG to p17 antigen. By the improved immunoassays, p24 antigen and antibody IgG to p17 antigen were detected earlier in 32 and 53%, respectively, of the HIV-1 seroconversion serum panels tested than before the improvements, and p24 antigen was detected as early as or earlier than HIV-1 RNA by reverse transcriptase-PCR (RT-PCR) in all of the panels tested. In 4 panels out of 19 tested, antibody IgG to p17 antigen or both antibodies IgG and IgM to p17 antigen were detected earlier than p24 antigen and RNA, although the antibody levels declined slightly before their steep increases usually observed after p24 antigen and RNA. Thus, the window period in diagnosis of HIV-1 infection can be shortened by detection of p24 antigen with the improved immunoassay as much as by detection of RNA with RT-PCR and, in some cases, more by detection of antibodies IgG and IgM to p17 antigen with the improved immunoassays than by detections of p24 antigen with the improved immunoassay and RNA with RT-PCR.

Recombinant p51 as antigen in an immune complex transfer enzyme immunoassay of immunoglobulin G antibody to human immunodeficiency virus type 1

An ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) of antibody immunoglobulin G (IgG) to human immunodeficiency virus type 1 (HIV-1) has been developed using recombinant HIV-1 reverse transcriptase (rRT) as antigen. However, some disadvantages were noted in the use of rRT as antigen: rRT was produced only with low efficiency in widely used strains of Escherichia coli using a rather long DNA fragment (3,012 bp) of the whole HIV-1 pol gene, and it was impossible to produce fusion proteins of RT for simple purification, since rRT is a heterodimer of p66 and p51. In this study, recombinant HIV-1 p51 and p66 with Ser-Ser at the N termini (Ser-Ser-rp51 and Ser-Ser-rp66) were produced in E. coli as fusion proteins with maltose binding protein containing a factor Xa site between the two proteins and were purified after digestion with factor Xa. Ser-Ser-rp51 was produced in larger amounts and purified in higher yields with less polymerization than Ser-Ser-rp66. Polymerized Ser-Ser-rp66 tended to be precipitated on mercaptoacetylation for conjugation to beta-D-galactosidase (used as a label) and showed higher nonspecific and lower specific signals in an immune complex transfer enzyme immunoassay of antibody IgG to HIV-1 than Ser-Ser-rp51. The signals for serum samples of HIV-1-seropositive subjects by immune complex transfer enzyme immunoassay of antibody IgG to HIV-1 using Ser-Ser-rp51 as antigen (Y) were well correlated to those obtained using rRT as antigen (X) (log Y = 0.99 log X + 0.23; r = 0.99). Thus, the use of rp51 as antigen was advantageous over that of rp66 and rRT in an immune complex transfer enzyme immunoassay of antibody IgG to HIV-1.

Immune complex transfer enzyme immunoassay for antibody IgM to HIV-1 p17 antigen

The immune complex transfer enzyme immunoassay for antibody IgM to HIV-1 p17 antigen is described. Serum samples containing antibody IgM to HIV-1 p17 antigen were incubated simultaneously with 2,4-dinitrophenyl-bovine serum albumin-recombinant p17 (rp17) conjugate and rp17-beta-D-galactosidase conjugate, and the immune complex formed comprising the three components was trapped onto colored polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG. Subsequently, the immune complex was transferred to white polystyrene beads coated with monoclonal mouse (antihuman IgM) IgG in the presence of excess of epsilonN-2,4-dinitrophenyl-L-lysine. The signal for antibody IgM to p17 antigen was the fluorescence intensity by fluorometric assay of beta-D-galactosidase activity bound to the white polystyrene beads. The periods of time required for the formation, trapping, and transferring of the immune complex comprising the three components were more than 4 hr, 2 hr, and 3 hr, respectively. The immunoassay developed was shown to be specific by inhibition of transferring the immune complex in the presence of excess of nonspecific IgM but not IgG. Signals for antibody IgM to p17 antigen with serum samples of HIV-1 seroconversion serum panels,--that is, with serum samples in early stages of the infection--tended to be higher than those with serum samples from HIV-1 asymptomatic carriers probably long after the infection and patients with ARC and AIDS. In contrast, signals for antibody IgG to p17 antigen with serum samples of HIV-1 seroconversion serum panels tended to be higher than signals for antibody IgM to p17 antigen but were much lower than signals for antibody IgG to p17 antigen with serum samples from HIV-1 asymptomatic carriers and patients with ARC and AIDS.

Rapid formation of the immune complexes on solid phase in the immune complex transfer enzyme immunoassays for HIV-1 p24 antigen and antibody IgGs to HIV-1

In order to perform the immune complex transfer enzyme immunoassays for HIV-1 p24 antigen and antibody IgGs to HIV-1 p17, reverse transcriptase and gp41 antigens as rapidly as possible, methods for rapid formation of the immune complexes on solid phase are described. HIV-1 p24 antigen was reacted with monoclonal anti-p24 Fab'-beta-D-galactosidase conjugate at a high concentration and subsequently with polystyrene beads coated successively with affinity-purified (anti-2,4-dinitrophenyl group) IgG and 2,4-dinitrophenyl-biotinyl bovine serum albumin-affinity-purified anti-p24 Fab' conjugate. Antibody IgGs to HIV-1 were reacted with polystyrene beads coated successively with affinity-purified (anti-2,4-dinitrophenyl group) IgG and 2,4-dinitrophenyl-HIV-1 antigen conjugates and subsequently with HIV-1 antigen-beta-D-galactosidase conjugates. The periods of time used for the formation of the immune complexes comprising the three components on the polystyrene beads (15-30 min) were much shorter than those used in the previous immune complex transfer enzyme immunoassays (90-300 min), and the sensitivities of the present and previous immune complex transfer enzyme immunoassays were similar. The detection limit of the HIV-1 p24 antigen by the present and previous methods were similar (3 to 10 zmol/assay).