Reliable confirmation of antibodies to human immunodeficiency virus type 1 (HIV-1) with an enzyme-linked immunoassay using recombinant antigens derived from the HIV-1 gag, pol, and env genes

Immunofluorescence assay reactivity patterns of serum samples presenting indeterminate Western blot results for antibodies to HIV-1 and HTLV-I/II in Cordoba, Argentina

Serum samples (n: 110) from blood donors and high risk individuals from Cordoba, Argentina with indeterminate HIV-1 and HTLV-I/II Wb profiles were studied for specific antibodies to HTLV-I/II and HIV-1 by indirect immunofluorescence assay (IFA) and for the presence or absence of HIV-1 and HTLV-I/II specific bands by Wb. This study was carried out in order to characterize their putative reactions with HIV-1 and HTLV-I/II proteins and to resolve the retrovirus infection status of these individuals. Results indicated that blood donors sera displaying indeterminate HIV-1 or HTLV-I/II Wb patterns were not immunoreactive to HTLV-I/II and HIV-1 on IFA. However, a high rate of indeterminate HIV-1 and HTLV-I/II Wb samples from high risk individuals had positive HTLV-I/II and HIV-1 IFA results respectively. Our study supports the growing evidence that HTLV-HIV indeterminate seroreactivity in low risk population is due to a cross reaction against nonviral antigens, and in high risk populations the indeterminate samples show serological cross-recognition between HIV-1 proteins and HTLV-I/II proteins on Wb. These results point out the necessity to investigate the HTLV-I/II reactivity in indeterminate HIV-1 samples and vice versa in order to confirm the diagnosis. Finally, this study shows the potential usefulness of IFA in elucidating the status of HIV-1 and HTLV-I/II infection of individuals with indeterminate Wb profiles, thus enabling resolution of retrovirus infection status.

More reliable diagnosis of infection with human immunodeficiency virus type 1 (HIV-1) by detection of antibody IgGs to pol and gag proteins of HIV-1 and p24 antigen of HIV-1 in urine, saliva, and/or serum with highly sensitive and specific enzyme immunoassay (immune complex transfer enzyme immunoassay): a review

Ultrasensitive enzyme immunoassays (immune complex transfer enzyme immunoassays) were developed for antibody IgGs to HIV-1 using recombinant reverse transcriptase (rRT), p17 (rp17), and p24 (rp24) as antigens. Antibody IgGs were reacted with 2,4-dinitrophenyl-recombinant antigens and recombinant antigen-beta-D-galactosidase conjugates, and the immune complexes formed, comprising the three components, were trapped onto polystyrene beads coated with (anti-2,4-dinitrophenyl group) IgG. After washing, the immune complexes were eluted from the polystyrene beads with excess of epsilon N-2,4-dinitrophenyl-L-lysine and were transferred to clean polystyrene beads coated with (antihuman IgG gamma-chain) IgG. beta-D-Galactosidase activity bound to the last polystyrene beads was assayed by fluorometry. By transfer of the immune complexes from one solid phase to another, the nonspecific binding of the beta-D-galactosidase conjugates was minimized and the sensitivity was markedly improved. The immune complex transfer enzyme immunoassays using rRT, rp17, and rp24 as antigens were 300-1,000-fold, 1,000-3,000-fold, and 30-100-fold, respectively, more sensitive than Western blotting for the corresponding antigens and 10-300-fold more sensitive than a conventional ELISA and a gelatin particle agglutination test. For urine (100 microliters), whole saliva (1 microliter), and serum (1 microliter) samples, the sensitivity and specificity of the immune complex transfer enzyme immunoassay using rRT as antigen were both 100%. However, for urine samples in which the specific activities of antibody IgG to RT, p17, and p24 were much lower than those in serum samples probably due to degradation by the kidney, a longer assay of bound beta-D-galactosidase activity or/and a concentration process for urine was required. The use of more than 1 microliter of whole saliva was recommended for reliable diagnosis of the infections, whereas 1 microliter of serum was sufficient for the purpose. The positivity with rRT as antigen could be confirmed by demonstration of antibody IgGs to p17 and p24 in most of the urine, whole saliva, and serum samples. In HIV-1 seroconversion serum panels, antibody IgG to p17 was detected as early as or even earlier than antibodies to HIV-1 by a conventional ELISA or/and a gelation particle agglutination test, whereas antibody IgGs to RT and p24 were detected as early as or later than antibody IgG to p17. Thus the uses of rRT and rp17 as antigens were advantageous over that of the other antigens for randomly collected serum samples probably long after the infection and serum samples at early stages of the infection, respectively. On the basis of these results and other reports, the immune complex transfer enzyme immunoassay was developed for simultaneous detection of p24 antigen and antibody IgGs to RT and p17 in a single assay tube, and the window period (8 weeks, although widely variable), during which diagnosis of HIV-1 infection is not possible due to the absence of detectable antibodies to HIV-1, was shortened by 2 weeks. As a result, the simultaneous detection made possible not only as early diagnosis as that by detection of p24 antigen, but also as reliable diagnosis as that by detection of antibodies to HIV-1. Finally, the immune complex transfer enzyme immunoassay has been recently improved so as to be performed within shorter periods of time (2-3 hr) with higher sensitivity, and testing many samples has become easy.

Profile of antigen-specific antibody response detectable by western blot in relation to diagnostic criteria for human immunodeficiency virus type-1 (HIV-1) infection

BACKGROUND

Variability in the profile of antigen-reactive bands in Western blot for serodiagnosis of human immunodeficiency virus (HIV) infection may result in disagreement regarding interpretation of positive result, due to lack of consensus in the interpretive criteria laid down by various organisations.

OBJECTIVES

The objectives of this study were (i) to find out the extent of disagreement over various criteria regarding interpretation of positivity in Western blot and (ii) to review the discordance by retesting the discordant specimens using recombinant antigens as well as by performing repeat Western blot in follow-up specimens.

STUDY DESIGN

A total of 467 specimens from high-risk groups, diagnosed positive for HIV type-1 (HIV-1) infection by the criteria of at least one of the five organisations, viz. Association of State and Public Health Laboratories Directors (ASTPHLD), Consortium for Retrovirus Serology (CRSS), American Red Cross (ARC) and World Health Organisation (WHO), were analysed to find out the extent of discordance between various criteria for interpretation of Western blot positivity. The discordant specimens were subjected to line immunoassay (LIA) using recombinant antigens. Also, follow-up Western blots were performed in case of discordant specimens at 6, 12 and 24 weeks intervals.

RESULTS

We observed that criteria laid down by ASTPHLD, CDC and CRSS scored all the specimens as positive while ARC and WHO criteria scored 13 (2.8%) and 18 (3.8%) of specimens, respectively, as negatives which were detected as positives by other criteria (discordant specimens). The gp41 reactive band was the most frequently missing band, being undetectable in 11.6% of specimens while bands reactive to p24, p31, gp120 and gp160 could not be recorded in 1.9%, 9.4% and 3.2% and 1.5.% of specimens, respectively. Testing of the discordant specimens with recombinant antigen preparation and with repeat Western blot in follow-up specimens collected at 6, 12 and 24 weeks demonstrated all bands undetectable in initial Western blot, except 25% of gp41 reactive bands.

CONCLUSIONS

It is felt that before selecting any criterion for Western blot positivity, it should be evaluated in the local population at risk for HIV-1 infection with additional or follow-up tests.

Immune complex transfer enzyme immunoassay that is more sensitive and specific than western blotting for detection of antibody immunoglobulin G to human immunodeficiency virus type 1 in serum with recombinant pol and gag proteins as antigens

Antibody immunoglobulin G (IgG) to human immunodeficiency virus type 1 (HIV-1) in serum was detected by ultrasensitive enzyme immunoassays (immune complex transfer enzyme immunoassays) with recombinant reverse transcriptase (rRT), p17 (rp17) and p24 (rp24) of HIV-1 as antigens and beta-D-galactosidase from Escherichia coli as the label. The immune complex, comprising 2,4-dinitrophenyl-bovine serum albumin-recombinant protein conjugate, antibody IgG to HIV-1, and recombinant protein-beta-D-galactosidase conjugate, was trapped on polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG, eluted with epsilon N-2,4-dinitrophenyl-L-lysine, and transferred to polystyrene beads coated with affinity-purified (anti-human IgG gamma-chain) IgG. Bound beta-D-galactosidase activity was assayed by fluorometry. The assays were highly reproducible with no serious serum interference, and they were much more sensitive than Western immunoblotting for the corresponding antigens. Signals with rRT, rp17, and rp24 for asymptomatic carriers were at least 56,000-, 680-, and 22-fold higher, respectively, than those for seronegative individuals, and neither indeterminate nor false-positive results were observed, whereas some serum samples were false negative or false positive by Western blotting for p17 and/or p24 antigen. In some cases, seroconversion was detected earlier than by conventional methods. Therefore, these assays are suggested to be more useful than conventional methods not only for the confirmation of antibody IgGs to RT, p17, and p24 of HIV-1 in serum but also for the detection of seroconversion.

Detection of antibodies to caprine arthritis-encephalitis virus using recombinant gag proteins

The coding sequences of the core proteins p17 and p28 of caprine arthritis-encephalitis virus (CAEV) were amplified using the polymerase chain reaction and cloned into the plasmid expression vector p-GEX-2T. Both p17 and p28 were expressed as fusion proteins with glutathione S-transferase. The recombinant proteins were affinity purified from induced bacterial lysates using glutathione-agarose beads. The purified proteins were used in an enzyme-linked immunosorbent assay (ELISA) to detect antibodies against CAEV in goat sera and milk samples. Three different ELISA tests were developed based on p17, p28 or the combination of these two recombinant proteins (p17 + p28). A comparison was made to an ELISA based on purified whole virus particles and to agar immunodiffusion test (AGID). Sera with conflicting results in the different ELISA tests were examined by Western blotting. There was a high correlation between the ELISA tests based on p17 + p28 recombinant proteins and whole virus ELISA, with an estimated kappa value of 0.92. Only 72-75% of the sera that tested positive in these two ELISA tests were positive in AGID. Antibodies to CAEV were detected in significantly more animals when serum samples were tested compared to milk samples. Based on the time and materials required to prepare the reagents, the recombinant based ELISA test was less expensive than the whole virus ELISA.

Microtiter enzyme-linked immunosorbent assay using recombinant derived antigens versus western blot in the confirmation of presence of antibodies against the human immunodeficiency virus type 1

A microtiter enzyme-linked immunosorbent assay using recombinant derived antigens was compared with the Western blot (Dupont) in the confirmation of the presence of antibodies against the human immunodeficiency virus type 1 (HIV-1). Of 104 sera (104 individuals) that were negative by a screening ELISA, 91 were also negative by both confirmation assays. In three sera only the microtiter assay was found to be indeterminate, and in nine other sera only Western blot. The only microtiter assay positive serum was from a male patient at risk for infection with HIV. 279 sera from 83 patients were found positive by screening. Of these, 223 sera were positive in both confirmation assays, and no serum was negative. Only one serum was indeterminate by the microtiter ELISA in contrast to 55 sera, including follow-up samples from 25 patients, most of whom had AIDS, by Western blot (Dupont criteria). However, the number of Western blot indeterminate sera decreased substantially applying less stringent criteria for interpretation. In conclusion, the microtiter ELISA performed well as a confirmation test for the presence of antibodies against HIV-1. In addition, the results demonstrate that in the microtiter assay the envelope peptide kp41 is highly discriminative in detecting anti-HIV-1 negative and anti-HIV-1 positive sera.

Viral-specific immunization in AIDS-related complex by photopheresis

The potential for therapeutic intervention in 7 patients with AIDS-related complex (ARC) was evaluated through the use of photopheresis. The rationale for the study was based on: 1. the demonstration that psoralen and UVA could inactivate HIV/virus in vitro; 2. CD4 cells are the primary target population effected by HIV and photopheresis; and 3. reinfusion of inactivated virus and cell-associated virus might serve to engender an immune response. Preliminary results in 7 patients with ARC over 6 to 18 months revealed a virus-specific response with an elevation of HIV antibodies, while EBV and CMV titers remained unchanged. The immunologic results revealed an increase in the CD8 lymphocyte population, stable activation markers (B2 microglobulin neopterin), a decrease in p24 antigen titers and inability to culture HIV virus in 3 patients. All of these results were in the context of a stable or increasing CD4+ percent. Six patients did not reveal a generalized inhibition of other immune responses as demonstrated by recovery of DTH. In addition, the resolution of lymphadenopathy, night sweats, fever and weight loss, paralleled the immunologic response.

In vitro measurement of antigen-specific cell-mediated immune responses using recombinant HIV-1 proteins adsorbed to latex microspheres

Recombinant proteins representing full-length and truncated forms of the human immunodeficiency virus type 1 envelope protein gp160 were produced in E. coli and sf9 insect cells. These proteins were denatured and reduced as a function of purification. We adsorbed these proteins onto latex microspheres and used the protein-coated particles as a vehicle to present the antigen in vitro to splenic mononuclear cells from immune mice. Recombinant proteins presented on the latex particles induced antigen-specific proliferative responses that were dependent on the antigen concentration. The proliferative responses were similar to those produced against an identical protein used in soluble form and equivalent protein concentrations. Latex microspheres coated with recombinant proteins could also induce precursor cytotoxic T lymphocytes to mature to functional effector cells in vitro. The use of the latex microspheres to present recombinant proteins as antigens allowed for the use of denatured proteins in our assay that were not soluble in aqueous solutions, such as cell culture media. This system of delivering recombinant proteins in vitro should greatly facilitate the use of recombinant proteins in assays involving live cells.

Expression in Escherichia coli and sequencing of the coding region for the capsid protein of Dutch maedi-visna virus strain ZZV 1050: application of recombinant protein in enzyme-linked immunosorbent assay for the detection of caprine and ovine lentiviruses

Maedi-visna in sheep and caprine arthritis-encephalitis in goats are caused by two closely related and widespread lentiviruses. The infections are characterized by life-long virus persistence and slow induction of antiviral antibodies. The diagnosis is based on the detection of antiviral antibodies. We have used the polymerase chain reaction (PCR) to amplify a part of the gag gene coding for the entire capsid protein and for parts of the matrix and nucleocapsid proteins. Sequencing of the PCR fragment of the Dutch maedi-visna virus strain ZZV 1050 revealed 85 and 92% homology to the DNA and deduced amino acid sequences, respectively, of the distantly related Icelandic visna virus strain 1514. The respective homologies with caprine arthritis-encephalitis virus strain CO were 76 and 80%. The PCR fragment was cloned into pGEX-2T and expressed as a glutathione S-transferase fusion protein. The recombinant protein could be detected on immunoblots by using a monoclonal antibody and polyclonal antisera and was further purified by glutathione-based affinity chromatography. Enzyme-linked immunosorbent assay with purified recombinant fusion protein is shown to be a sensitive and specific diagnostic tool for the detection of lentiviral infection in goats and sheep.

Continuous epitopes of the human immunodeficiency virus type 1 (HIV-1) transmembrane glycoprotein and reactivity of human sera to synthetic peptides representing various HIV-1 isolates

Immunoreactive regions of human immunodeficiency virus type 1 (HIV-1) gp41 were mapped by reacting HIV-1 antibody-positive human sera with overlapping synthetic peptides which covered the transmembrane protein. Three immunoreactive domains were identified, and five different and partially overlapping epitopes recognized by HIV-1-positive human sera were found within one immunodominant region. The effect on antibody recognition after single amino acid substitutions within one defined epitope was also studied. The reactivity of various HIV-1-positive sera to synthetic peptides with amino acid substitutions representing known isolates suggests an important substitution in the major epitope of African HIV-1 strains.

Development and evaluation of a human T-cell leukemia virus type I serologic confirmatory assay incorporating a recombinant envelope polypeptide

A recombinant protein derived from the gp21 region of the human T-cell leukemia virus type I (HTLV-I) env gene was synthesized in Escherichia coli and purified by reversed-phase high-performance liquid chromatography. The purified protein was free of contaminating bacterial proteins and retained reactivity with human HTLV-I- and HTLV-II-positive sera and a gp21 monoclonal antibody. An immunoblot procedure using the recombinant polypeptide in conjunction with native viral proteins was more sensitive than the conventional immunoblot and radioimmunoprecipitation confirmatory assays for detection of antibodies to HTLV-I and HTLV-II env-encoded gene products. The recombinant protein was equally reactive with sera from polymerase chain reaction-confirmed HTLV-I or HTLV-II infections. Furthermore, on the basis of the differential reactivities of gp21-positive sera with the HTLV-I p19 and p24 gag-encoded proteins, an algorithm was proposed to distinguish exposure to HTLV-I from exposure to HTLV-II. These results establish the utility of a modified immunoblot assay incorporating a recombinant envelope polypeptide as an alternative to existing HTLV-I-confirmatory assays.