Whole saliva dried on filter paper or diagnosis of HIV-1 infection by detection of antibody IgG to HIV-1 with ultrasensitive enzyme immunoassay using recombinant reverse transcriptase as antigen

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.

Mapping of B-cell epitopes in rabbits immunised with various gag antigens for the production of HIV-1 gag capture ELISA reagents

An HIV-1 p24 capture enzyme linked immunosorbent assay (ELISA) was developed and used in a study of B-cell epitopes in rabbits immunised with different gag p24 antigens. Rabbits were immunised with virion HIV-1/Lai, baculovirus recombinant p24, Escherichia coli recombinant p24-15 and a mixture of synthetic peptides representing sequences of HIV-1 gag p24 protein, respectively. Five out of nine rabbits developed antibodies that could be used for an antigen capture ELISA. No significant differences in IgG titers to the whole gag protein were seen when comparing rabbits immunised with four different antigens. Three major common linear epitope regions were mapped in the rabbits immunised with virion HIV-1/Lai and baculovirus recombinant p24. The rabbit immunised with HIV-1 gag peptides had the broadest linear epitope reactive responses whereas animals immunised with E. coli recombinant antigen had the most restricted linear epitope response. The capture ELISA method thus developed using the different rabbit anti-p24 IgG preparations was shown to capture isolates from HIV-1 subtypes or clades A to G. Only rabbits immunised with virion HIV-1/Lai and baculovirus recombinant p24 developed IgG that was capable of efficiently capturing HIV-1 p24 in ELISA, indicating the importance of preparing antibodies able to recognise native or discontinuous and linear antigen configurations.

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.

Optimal conditions of immune complex transfer enzyme immunoassay for p24 antigen of HIV-1

In the immune complex transfer enzyme immunoassay for HIV-1 p24 antigen, different preparations of anti-p24 Fab'-beta-D-galactosidase conjugate, various periods of time for immunoreactions involved, and shaking for incubations with polystyrene beads were tested. On the basis of the results of these experiments, p24 antigen was measured as follows. The antigen was reacted simultaneously with 2,4-dinitrophenyl-biotinyl-bovine serum albumin-affinity-purified rabbit anti-p24 Fab' conjugate and highly polymerized monoclonal mouse anti-p24 Fab'-beta-D-galactosidase conjugate at 37 degrees C for 2 hr. The immune complex formed comprising the three components was trapped onto colored polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG for 1.5 hr and was transferred to white polystyrene beads coated with streptavidin in the presence of epsilon N-2,4-dinitrophenyl-L-lysine for 1.5 hr. The incubations with polystyrene beads were performed at room temperature with shaking. beta-D-Galactosidase activity bound to the white polystyrene beads was assayed by fluorometry at 30 degrees C for 2 hr. The detection limit of p24 antigen (0.1 amol/tube and 10 amol (0.24 pg)/ml of serum) was equal to that obtained when the formation, trapping, and transferring of the immune complex were performed for 4, 16, and 3 hr, respectively, by incubation without shaking. Namely, the period of time required for the immune complex transfer enzyme immunoassay of p24 antigen was markedly shortened (25.5-7 hr) without loss of the sensitivity. By the improved immune complex transfer enzyme immunoassay, p24 antigen was detected 12-20 days earlier than the detection of antibodies to HIV-1, i.e., seroconversion by the conventional ELISA.

More sensitive immune complex transfer enzyme immunoassay for antibody IgG to p17 of HIV-1 with shorter incubation time for immunoreactions and larger volumes of serum samples

In the previous immune complex transfer enzyme immunoassay for antibody IgG to p17 of HIV-1, the immune complex comprising 2,4-dinitrophenyl-bovine serum albumin-recombinant p17 conjugate, anti-p17 IgG, and recombinant p17-beta-D-galactosidase conjugate was trapped onto polystyrene beads coated with (anti-2,4-dinitrophenyl group) IgG by overnight incubation and was transferred to polystyrene beads coated with (antithuman IgG gamma-chain) IgG by 3 hr incubation in the presence of excess of epsilon N-2,4-dinitrophenyl-L-lysine. These processes were made efficient by incubation with shaking and by using solid phases with larger surface areas. In addition, the volume of serum samples used was increased from 10 microliters to 100 microliters. As a result, the sensitivity was improved 20-30-fold and was approximately 100,000-fold higher than that of Western blotting for p17 band, even when both trapping and transferring of the immune complex were performed for only 30 min. Furthermore, testing many samples became easily possible with higher sensitivity using microplates and a fluororeader.

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).