Seven human immunodeficiency virus (HIV) antigen-antibody combination assays: evaluation of HIV seroconversion sensitivity and subtype detection

In this study, we evaluated the performance of two prototype human immunodeficiency virus (HIV) antigen-antibody (Ag-Ab) combination assays, one from Abbott Laboratories (AxSYM HIV Ag-Ab) and the other from bioMerieux (VIDAS HIV Duo Ultra), versus five combination assays commercially available in Europe. The assays were Enzygnost HIV Integral, Genscreen Plus HIV Ag-Ab, Murex HIV Ag-Ab Combination, VIDAS HIV Duo, and Vironostika HIV Uniform II Ag-Ab. All assays were evaluated for the ability to detect p24 antigen from HIV-1 groups M and O, antibody-positive plasma samples from HIV-1 groups M and O, HIV-2, and 19 HIV seroconversion panels. Results indicate that although all combination assays can detect antibodies to HIV-1, group M, subtypes A to G, circulating recombinant form (CRF) A/E, and HIV-1 group O, their sensitivity varied considerably when tested using diluted HIV-1 group O and HIV-2 antibody-positive samples. Among combination assays, the AxSYM, Murex, and VIDAS HIV Duo Ultra assays exhibited the best antigen sensitivity (at approximately 25 pg of HIV Ag/ml) for detection of HIV-1 group M, subtypes A to G and CRF A/E, and HIV-1 group O isolates. However, the VIDAS HIV Duo Ultra assay had a lower sensitivity for HIV-1 group M and subtype C, and was unable to detect subtype C antigen even at 125 pg of HIV Ag/ml. The HIV antigen sensitivity of the VIDAS HIV Duo and Genscreen Plus combination assays was approximately 125 pg of HIV Ag/ml for detection of all HIV-1 group M isolates except HIV-1 group O while the sensitivity of Vironostika HIV Uniform II Ag-Ab and Enzygnost HIV Integral Ag-Ab assays for all the group M subtypes was >125 pg of HIV Ag/ml. Among the combination assays, the AxSYM assay had the best performance for detection of early seroconversion samples, followed by the Murex and VIDAS HIV Duo Ultra assays.

Long-term protease inhibitor-containing therapy results in limited improvement in T cell function but not restoration of interleukin-12 production in pediatric patients with AIDS

This study investigated whether immune restoration occurred in 26 human immunodeficiency virus (HIV) type 1-infected children treated first with indinavir for 16 weeks and then with combination antiretroviral therapy for >2 years. Compared with baseline, a significant, although modest, decrease in virus loads (maximum median, -0.86 log(10)) and increase in the number of CD4(+) lymphocytes, especially naive cells, were observed at several time points after 2 years. A maximum of 7% of treated children achieved undetectable viremia. There was a marked increase in the proliferative response and skin reactivity to recall antigens. However, responses to an HIV antigen remained depressed, and the production of interleukin-12 remained unchanged and abnormally low. The magnitude of virus suppression did not correlate with these measures of functional immune reconstitution. These findings suggest that long-term nonsuppressive antiretroviral therapy can induce limited improvement in immune function in pediatric AIDS patients and that the effect of suppressive treatments should be investigated.

Shortening of the diagnostic window with a new combined HIV p24 antigen and anti-HIV-1/2/O screening test

Because antibodies to the human immunodeficiency virus (HIV) are absent in the very early phase of HIV infection, there remains a slight residual risk for HIV transmission by blood donations by viremic but antibody negative donations. To shorten the diagnostic window between infection and the detection of antibodies, Enzygnost HIV Integral (Dade Behring, Germany) was developed. With this new test, HIV p24 antigen and HIV antibodies can be detected simultaneously in a single test. In a multicenter study the new screening assay has been compared with various tests that detect only HIV antibodies or HIV p24 antigen and with assays which permit a simultaneous detection of HIV antigen and HIV antibodies. The new assay showed 100% sensitivity for the detection of antibodies to HIV-1, groups M (n=1102) and O (n=55), and HIV-2 (n=289). In 23 out of 52 seroconversion panels, seroconversion was detected 2-18 days earlier with the new combined antigen/antibody test compared to single antibody tests. All samples from a viral load panel (n=451), all samples containing p24 antigen (n=302), and all but one of the cell culture supernatants (n=38) infected with various HIV-1 subtypes or HIV-2 were identified reliably by the new test. The specificity of the assay for 4002 unselected blood donors was 99.78% initially and 99.80% after retesting. Potentially interfering factors had no systematic influence on specificity. By testing for p24 antigen, which is present prior to the onset of antibody production in some cases of recent HIV infection, the new assay reduces the diagnostic window as compared to third generation screening assays, thus permitting an earlier diagnosis of HIV infection.

[Diagnosis and virologic monitoring of HIV infection]

The new challenge of the diagnosis of HIV infection concerns the treatment since an early diagnosis permits to start antiretroviral therapy with the aim to block the evolution to aids. The virological diagnosis may be done easily using new sensitive and specific techniques. Using the test of detection of p24 antigenemia and HIV-RNA in plasma, it is easy to approach the diagnosis of primary infection. The tests for HIV viral load are now largely available and they must be systematically included in the follow-up of infected persons.

[Evaluation of a new screening assay kit for the combined detection of HIV p24 antigen and antibody--comparison of the performance of the new kit and HIV antibody assay kits]

DUO is an automated HIV infection screening test kit based on the combined detection of p24 Ag and anti-HIV-1 and anti-HIV-2 IgG in human sera or plasma using the ELFA technique (Enzyme-Linked Fluorescent Assay). The performance of DUO was compared with that of HIV-1/HIV-2 3rd generation EIA plus and particle agglutination (PA) test. A total of 141 seropositive sera, 3 seroconversion panels, 300 seronegative sera and 387 potentially cross-reactive serum samples were tested. One hundred and forty one seropositive sera in Japan and Cameroon were all positive with DUO. Three seroconversion panels (panel Q, Z, AE) were tested to evaluate sensitivity. In Panel Q, infecution was detected seven days earlier with DUO than with the 3rd generation EIA plus and PA. In Panel AE, infection was detected four days earlier with DUO than with the single antibody assays. Three hundred seronegative sera from Kanagawa prefectural public health centers were all negative with DUO as well as PA test. Three hundred and eighty seven potentially cross-reacting samples were tested to challenge the specificity of the assay. These included samples from pregnant women and hepatitis patients. In four of the 204 samples from pregnant women, false-positive results were observed with DUO. In three of the 183 samples from hepatitis patients, false-positive results were also obtained with DUO. All samples of 7 DUO positive results were negative with western blot test. Five of them were negative with RT-PCR and 2 of them were not tested because there were not enough samples. Thirty cross-reacting (false-positive) samples by PA test from blood donors were tested by DUO, and all of these were negative by DUO.

Rapid and ultrasensitive enzyme immunoassay (thin aqueous layer immune complex transfer enzyme immunoassay) for HIV-1 p24 antigen

The immune complex transfer enzyme immunoassay for HIV-1 p24 antigen was performed in three different ways (in the present immunoassays I, II, and III) within much shorter periods of time than previously reported. In the present (simultaneous) immunoassay I, p24 antigen was incubated simultaneously with 2,4-dinitrophenyl-biotinyl-bovine serum albumin-affinity-purified rabbit anti-p24 Fab' conjugate and monoclonal mouse anti-p24 Fab'-beta-D-galactosidase conjugate in a total volume of 19 microL for 15 min to form the immune complex comprising the three components. The reaction mixture was incubated with a polystyrene bead of 6.35 mm in diameter coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG for 5 min to trap the immune complex. After washing, the polystyrene bead was incubated with 35 microL of epsilonN-2,4-dinitrophenyl-L-lysine for 15 min to elute the immune complex (the first eluate) and, after removing the first eluate, with an additional 35 microL of epsilonN-2,4-dinitrophenyl-L-lysine for 1 min (the second eluate). The first and second eluates were incubated with a polystyrene test tube (12 x 75 mm) coated with streptavidin for 15 min. In the present (sequential) immunoassay II, a polystyrene bead of 6.35 mm in diameter successively coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG and 2,4-dinitrophenyl-biotinyl-bovine serum albumin-affinity-purified rabbit anti-p24 Fab' conjugate was incubated with p24 antigen in a total volume of 20 microL for 5 min and subsequently with monoclonal mouse anti-p24 Fab'-beta-D-galactosidase conjugate in a volume of 5 microL for 20 min. The immune complex formed on the polystyrene bead was transferred to a polystyrene test tube coated with streptavidin as described above. In the present (sequential) immunoassay III, p24 antigen was incubated with monoclonal mouse anti-p24 Fab'-beta-D-galactosidase conjugate in a total volume of 19 microL for 10 min and with a polystyrene bead of 6.35 mm in diameter coated successively with affinity-purified (anti-2,4-dinitrophenyl group) IgG and 2,4-dinitrophenyl-biotinyl-bovine serum albumin-affinity-purified rabbit anti-p24 Fab' conjugate for 20 min. The immune complex formed on the polystyrene bead was transferred as described above. The incubations were performed at room temperature either by shaking the polystyrene beads (one/assay) and the reaction mixtures in styrol test tubes (13.3 x 54 mm and 2.1 g) so as to randomly rotate the polystyrene beads or by rotating the polystyrene test tubes (12 x 75 mm) containing the reaction mixtures, so that small drops (19 to 70 microL) of the reaction mixtures evenly contacted all parts of the solid phase surfaces during the incubations (although they contacted only small parts of the solid phase surfaces at a time) to continuously mix thin aqueous layers covering the solid phase surfaces with the rest of the reaction mixtures. (Therefore, these immunoassays are called thin aqueous layer immunoassays.) The detection limits of p24 antigen by 1 hr assay of bound beta-D-galactosidase activity in the present immunoassays I, II, and III were 0.1, 0.2 and 0.1 amol/assay, respectively, and were slightly higher than or equal to that by the previously reported immune complex transfer enzyme immunoassay, in which the immune complex was formed for 4 hr, was trapped for 16 hr, and was transferred for 3 hr followed by 1-hr assay of bound beta-D-galactosidase activity. By 20-hr assay of bound beta-D-galactosidase activity, the detection limit of p24 antigen was further lowered to 10 zmol/assay in the present (simultaneous) immunoassay I and to 3 zmol/assay in the present (sequential) immunoassay III. However, the nonspecific reaction(s) with serum samples from HIV-1 seronegative subjects hampered the improvement of the detection limit by 20-hr assay of bound beta-D-galactosidase activity.

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).

Immune complex transfer enzyme immunoassay for antibody IgG to HIV-1 gp41 antigen using synthetic peptides as antigens

The immune complex transfer enzyme immunoassay for antibody IgG to HIV-1 gp41 antigen was developed using two synthetic peptides. An aliquot (10 microl) of serum samples from HIV-1 seropositive subjects was incubated simultaneously with 2,4-dinitrophenyl-bovine serum albumin-synthetic HIV-1 gp41 peptide conjugates and synthetic HIV-1 gp41 peptide-beta-D-galactosidase conjugates and subsequently with colored polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG to trap the immune complexes formed comprising the three components. After washing, the colored polystyrene beads were incubated with white polystyrene beads coated with affinity-purified (anti-human IgGgamma-chain) IgG in the presence of epsilonN-2,4-dinitrophenyl-L-lysine to transfer the immune complexes to the white polystyrene beads. Beta-D-Galactosidase activity bound to the white polystyrene beads was assayed by fluorometry. The formation, trapping and transferring of the immune complexes were completed within 0.5, 0.5 and 1.5 hr, respectively. Since each peptide appeared to react with its own specific antibody IgG, serum samples were tested by the equimolar combination of the two peptides. The lowest signals (fluorescence intensities for bound beta-D-galactosidase activity) for serum samples from HIV-1 asymptomatic carriers, patients with AIDS-related complex and patients with AIDS were 1490-, 2210- and 1460-fold, respectively, higher than the highest signal for serum samples from HIV-1 seronegative subjects. In five seroconversion serum panels, antibody IgG to HIV-1 gp41 antigen was detected as early as antibodies to HIV-1 detected by three currently commercially available methods.

Development of a neutralizing antibody response during acute primary human immunodeficiency virus type 1 infection and the emergence of antigenic variants

We monitored the primary humoral response to human immunodeficiency virus type 1 infection and showed that, in addition to antibodies to p24 and gp41, antigens which form the basis of most diagnostic assays, the response included a significant antibody response directed to the gp120 region of the infecting viral quasispecies. When tested in a recombinant virus neutralization assay, these antibodies were capable of inhibiting viral growth. We found the primary viral quasispecies to solely utilize the CCR-5 chemokine receptor; however, recombinant viruses differed in their cytopathology and in their sensitivity to beta-chemokine inhibition of viral growth. Sequence analysis of the gp120 open reading frames showed that amino acid changes in the C1 (D-->G at position 62) and C4 (V-->A at position 430) regions accounted for the phenotypic differences. These data demonstrate that early in infection, polymorphism exists in envelope glycoprotein coreceptor interactions and imply that therapeutic strategies targeted at this step in the viral life cycle may lead to rapid resistance.

Rhesus macaques that become systemically infected with pathogenic SHIV 89.6-PD after intravenous, rectal, or vaginal inoculation and fail to make an antiviral antibody response rapidly develop AIDS

A new simian-human immunodeficiency virus (SHIV) stock (SHIV 89.6-PD), derived from plasma of a rhesus macaque used for in vivo serial passage of virulence-attenuated SHIV 89.6, produces systemic infection after intravenous, intravaginal, or intrarectal inoculation of rhesus macaques. Infection with this virus results in high levels of viral antigen in plasma, a precipitous decline in CD4+ T-cell counts, and a disease syndrome that is characteristic of AIDS. Rapid progression to disease was associated with failure to seroconvert to viral antigens, whereas longer survival was associated with production of antiviral antibodies. In intravenously inoculated animals, peak antigenemia occurred at 7 days postinjection (PI) and severe CD4+ depletion occurred at 14 days PI. In mucosally infected animals, peak antigenemia occurred at 14 days PI and severe CD4+ depletion was not evident until 21 days PI. The 1-week delay in both viral antigenemia and CD4+ T-cell decline in mucosally infected animals is consistent with the hypothesis that, following vaginal inoculation, virus dissemination proceeds in a stepwise manner from the mucosal surface to the draining lymph nodes and subsequently to the bloodstream. This animal model can be used to test the ability of HIV-1 envelope-based vaccines to prevent infection or disease after challenge by the three major routes of HIV transmission.

Design and evaluation of an in-house HIV-1 (group M and O), SIVmnd and SIVcpz antigen capture assay

An enzyme-linked immuno-sorbent assay (ELISA) for the detection of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIVcpz/SIVmnd) antigens was designed using immunoreagents from naturally infected individuals, and compared to the commercially available Vironostika HIV-1 Antigen Microelisa System (Organon Teknika). The in-house assay proved to be specific for HIV-1 isolates belonging to group M (A-H) and group O and for SIVcpz and SIVmnd isolates, but was less sensitive than the Vironostika HIV-1 Antigen Microelisa System, except for SIVmnd. For the strains belonging to HIV-2, SIVmac and SIVagm, the in-house assay could not detect antigen to an appreciable degree. This study shows that a considerably less expensive but sufficiently accurate HIV-1 antigen capture assay can be developed to monitor HIV-1 (group M and O), SIVcpv and SIVmnd antigen in the supernatants of virus cultures.

HIV-1 and HIV-2 dual infection: lack of HIV-2 provirus correlates with low CD4+ lymphocyte counts

OBJECTIVE

We conducted this study to genetically characterize dual infection in individuals demonstrating a dual serological profile.

METHODS

All subjects were first evaluated by immunoblot for antibody reactivity to the major viral antigens for HIV-1 and HIV-2. Sera were judged to be dual-seropositive if they reacted with strong and equal intensity with the envelope antigens of both HIV-1 and HIV-2 and were confirmed with type-specific recombinant env peptides. We used nested polymerase chain reaction (PCR) to amplify proviral gag and env sequence from peripheral blood mononuclear cell (PBMC) DNA from HIV-1- and HIV-2-infected individuals. Positive amplification was detected after Southern blot hybridization.

RESULTS

Plasmid dilution and mixing showed equivalent sensitivity of HIV-1 and HIV-2 primers that was not altered by heterologous target sequences. The DNA PCR showed 100% sensitivity and specificity for detection of monotypic HIV infection. Serologically defined HIV-dual reactives were evaluated by this assay, with 100% detection in female sex workers (21 out of 21), but only 38.5% detection (five out of 13) in hospitalized patients; all being HIV-1 positive only. The lack of HIV-2 proviral signal was significantly correlated with low CD4+ lymphocyte counts (Pvalue = 0.04).

CONCLUSION

The results suggest that HIV dual infection may not be a static condition. Levels of HIV-2 may decrease with disease progression or sequester in tissue reservoirs; our results may also suggest that HIV-1 effectively overgrows HIV-2 in the dually exposed host individual.

Cultured blood dendritic cells retain HIV-1 antigen-presenting capacity for memory CTL during progressive HIV-1 infection

Dendritic cells (DC) are potent APC that may be involved in the pathogenesis of HIV-1 infection. We studied the APC function of DC from HIV-1-infected subjects that were derived from monocyte-depleted PBMC by culture in human IL-4 and human granulocyte-macrophage CSF. The cultured cells from the HIV-1-infected subjects had similar morphology and phenotype of mature DC (CD80 = 41 +/- 8%, CD86 = 77 +/- 5%, CD40 = 87 +/- 6%, CD1a = 1 +/- 1%) to DC cultured from seronegative subjects. The yield of these DC was lower than from HIV-1-seronegative subjects (4 +/- 0% vs 11 +/- 2%, p < 0.01), and the lower DC yields correlated with lower numbers of blood CD4+ T cells (r = 0.60, p < 0.01) and higher plasma viral load (r = -0.49, p < 0.01). DC from HIV-1-infected subjects were infected with recombinant vaccinia virus vectors expressing Gag, Pol, and Env and were able to stimulate equal or higher levels of MHC class I-restricted, anti-HIV-1 memory CTL (CTLm) than were similarly treated, autologous B lymphocyte cell lines. DC pulsed with peptides representing HIV-1 CTL epitopes stimulated higher levels of anti-HIV-1 CTLm responses than did DC infected with the vaccinia virus-HIV-1 constructs. Allogeneic, MHC class I-matched DC also stimulated anti-HIV-1 CTLm activity in cells from HIV-1-infected subjects. DC from early and late stages of HIV-1 infection had a similar ability to activate CTLm specific for targets expressing either HIV-1 genes via vaccinia virus vectors or HIV-1 immunodominant synthetic peptides. However, DC from either early or late stages of HIV-1 infection could not overcome the defect in anti-HIV-1 CTLm response in advanced infection.

Detection of HIV-1 window period infection in blood donors using borderline anti-HIV results, HIV-1 proviral DNA PCR, and HIV-1 antigen test

Prevention of transmission of HIV-1 via blood transfusion has been carried out by the National Blood Center by screening donated blood with anti-HIV and HIV antigen tests. To increase the safety measure, detection of proviral DNA by PCR has been proposed; however, it was impractical to test all samples by PCR. From August 1994 to September 1995, there were 296,169 blood donors with 0.32 per cent prevalence of anti-HIV positive. From these donors, 153 samples of which the anti-HIV enzyme immunoassay optical density (OD) between cutoff and 80 per cent of cutoff value (borderline results) were selected for PCR testing. One out of 153 borderline cases showed positive by PCR test for HIV-1 proviral DNA. However, this case was also positive by HIV antigen test. Therefore, most of the samples with borderline anti-HIV results were true negative for HIV infection. On the other hand, there were 8 HIV antigen positive samples which had anti-HIV OD below the borderline value determined in this study. This finding confirmed the necessity of using both the anti-HIV and HIV antigen tests for screening of donated blood.

High serum level of soluble CD30 in acute primary HIV-1 infection

CD30 has been suggested to play a role in HIV infection. In this study the serum concentration of soluble CD30 (sCD30) was determined by an ELISA essay on samples collected from patients with acute primary HIV-1 infection during the acute phase (n = 17) and after seroconversion (n = 13). sCD30 during acute infection was consistently elevated (137.58 +/- 120.33 versus 6.4 +/- 5.4 U/ml (mean +/- s.d.) in normal controls, P<0.0001) and decreased after seroconversion (49.1 +/- 66.17 U/ml; P = 0.0018 compared with acute infection). This trend mirrored the disappearance of detectable levels of HIV antigen in the blood, resulting in a direct correlation between sCD30 and HIVAg values (P = 0.002). These data suggest that the high levels of sCD30 observed during the peak concentration of HIVAg in acute primary HIV infection might reflect the high rate of viral replication.

Simple monitoring of antiretroviral therapy with a signal-amplification-boosted HIV-1 p24 antigen assay with heat-denatured plasma

OBJECTIVE

Virus load determination has become indispensable for the management of HIV patients, but depends on expensive assays of a low throughput. We evaluated whether a highly improved HIV-1 p24 antigen detection procedure which involves heat-mediated immune complex dissociation and signal-amplification-boosted enzyme-linked immunosorbent assay (ELISA) was suitable for antiretroviral treatment monitoring.

DESIGN AND METHODS

Virus load in plasma was determined for 127 plasma samples taken at 0, 2, 6, 12, 18, 24, 30 and 36 weeks from 23 patients with CD4+ T cells < 50 x 10(6)/l who received indinavir 800 mg three times daily in addition to prior antiretroviral treatment. Tests included polymerase chain reaction (PCR) for viral RNA, measured prospectively with the Roche Amplicor kit, and retrospective batch testing of heat-denatured samples for p24 antigen by the DuPont HIV-1 p24 Core Profile ELISA linked with a tyramide signal amplification step. Particle-associated reverse transcriptase (RT) by the product-enhanced RT (PERT) assay was determined as an independent third-opinion viral load marker.

RESULTS

p24 antigen was detected as sensitively as viral RNA. Overall detection during a median observation time of 25 weeks (range, 0-39) amounted to 75.6% for antigen and 73.6% for RNA. The antigen detection limit was 0.2 pg/ml. Antigen was detectable in all 23 baseline samples, whereas RNA was undetectable in one. Antigen and RNA levels in 79 samples positive for both markers correlated with r = 0.714 (P < 0.0001). Average changes in levels of p24 antigen and RNA at eight timepoints correlated with r = 0.982 (P < 0.0001). In individual patients, the two parameters behaved similarly, and in certain cases virtually identically. RT activity was measurable in all samples.

CONCLUSIONS

The performance of this antigen detection procedure is comparable to RNA PCR, thus providing a simple, high throughput alternative in monitoring the efficacy of antiretroviral treatment.

Lack of predictive value for progression of dissociated circulating P24 antigen in human immunodeficiency virus type 1-infected black patients

In human immunodeficiency virus type 1 (HIV)-1-infected Black people, the circulating p24 antigen is hidden frequently in immune complexes, because of high titers of serum anti-p24 antibodies. In order to evaluate the prognostic values for progression of free and dissociated serum p24 antigen in Black people, sera from 45 HIV-1-infected Black patients, all at non-AIDS stages, were evaluated prospectively for p24 antigen by several assays; circulating free p24 antigen was measured by immunocapture ELISA only (method 1) and with ELAST amplification (method 2), and dissociated p24 antigen determined after glycine-HCl pretreatment of serum, by immunocapture ELISA only (method 3) and with ELAST amplification (method 4). Serum CD4 and CD8 cell counts, beta 2-microglobulin, and total IgA were determined also at least twice a year. Clinical events for AIDS were those included in the 1986 CDC classification for HIV infection. At entry, p24 antigen was found in 3 (6.7%) patients by method 1, in 7 (15.6%) by method 2, in 14 (31.1%) by method 3, and in 22 (48.9%) by method 4. Methods 3 and 4 were more sensitive than method 1 (P < 0.001) and method 2 (P < 0.001). The mean follow-up was 30 months. The free symptom survival times (mean +/- SD months) were significantly lower in patients being p24 antigen positive by method 1 [(+) 33 +/- 27 vs. (-) 61 +/- 15, P = 0.03), but they were similar in patients positive and in those negative for p24 antigen determined by method 2 [(+) 71 +/- 17 vs. (-) 74 +/- 9, P = 0.54], method 3 [(+) 76 +/- 12 vs. (-) 69 +/- 13.2, P = 0.80], and method 4 [(+) 79 +/- 9 vs. (-) 63 +/- 7, P = 0.71]. At 24 months, p24 antigen positivity did not correlate either with CD4 or CD4/CD8 slops, nor with beta 2-microglobulin or IgA variations. By contrast, a CD4 cell count below 200/mm3 at entry was significantly associated with disease progression. In conclusion, dissociated p24 antigenemia does not appear as a useful surrogate marker for progression in HIV-1-infected Black people.

Racial differences in rate of CD4 decline in HIV-1-infected homosexual men

OBJECTIVE

To determine whether racial differences exist in the rate of CD4 lymphocyte decline in HIV-1-infected homosexual men.

DESIGN

Prospective cohort study.

STUDY POPULATION

Non-Hispanic white (n = 321) and black (n = 102) HIV-1-seropositive homosexual and bisexual men were recruited from the Baltimore/Washington, DC metropolitan areas between 1984-1985 and 1987-1990, and evaluated semiannually.

MAIN MEASUREMENTS

Changes in CD4 lymphocyte count and CD4 percentage over time were analysed using linear regression methods for the 271 white and 69 black participants who had at least four semiannual CD4 lymphocyte measurements.

RESULTS

Rate of decline in CD4 lymphocyte count over 6 months was much slower among black than white seroprevalent men at all levels of baseline CD4 count (baseline 201-400 x 10(6)/l: + 0.24 versus -17.7 x 10(6)/l; 401-600 x 10(6)/l: -11.3 versus -23.9 x 10(6)/l; 601-800 x 10(6)/l: -15.1 versus -35.2 x 10(6)/l; > 800 x 10(6)/l: -4.3 versus -42.7 x 10(6)/l for black versus white, respectively), although this was only statistically significant for the lowest and highest strata of baseline CD4 count. These racial differences persisted after adjustment for recruitment period (1984-1985 or 1987-1990), follow-up duration, age and zidovudine therapy or Pneumocystis carinii pneumonia prophylaxis. Similar findings were observed among the 70 white and 11 black seroconverters. Black participants were also less likely than a subgroup of white participants matched on baseline CD4 lymphocyte count to be HIV-1 p24 antigen-positive. However, after acid dissociation of samples initially p24 antigen-negative, there were no significant differences in the prevalence of p24 antigenemia at enrollment or after 1 year of follow-up.

CONCLUSIONS

This analysis suggests a more gradual decline in CD4 lymphocyte count among black than white Americans. The clinical significance of and reasons for this are unclear, but the lower prevalence of p24 antigenemia due to immune complexing among black Americans suggests that racial differences in the immune response to HIV may exist. Additional studies are needed to validate these findings in a larger cohort of non-whites, and to assess their relationship with other measures of cell-mediated immune function.