Prognostic importance of antibodies to human immunodeficiency virus by recombinant immunoassay and Western blot techniques in HIV antibody-positive hemophiliacs

Characterization of HIV-1-specific antibodies and HIV-1-crossreactive antibodies to platelets in HIV-1-infected haemophiliac patients

Sera from HIV-1-infected haemophiliacs were examined for human immunodeficiency virus (HIV) specific antibodies and for platelet crossreactive antibodies. Using HIV sepharose 4B affinity columns for serum absorption, antibodies against various HIV antigens, including HIV lysate. HIV-p24 and HIV-gp120, were eluted either by low or by high pH buffer. The eluates were examined by ELISA for HIV specificity and by flow cytometry for platelet crossreactivity. Two types of HIV antibodies could be eluted, i.e. acid-sensitive and alkaline-sensitive antibodies. HIV antibodies were obtained in 26/29 acid eluates and in 25/29 of the alkaline eluates from HIV-lysate columns; 96% (25/26) of the acid-eluted antibodies were HIV-specific but 48% (12/ 25) of the alkaline-eluted antibodies also showed crossreactivity to platelets. Of the 20 alkaline-eluted HIV-p24 antibodies, 40% (8/20) reacted specifically with HIV-p24 and 60% (12/20) were platelet crossreactive. In contrast, of the alkaline-eluted HIV-gp120 antibodies (n=17), 88% (15/17) were HIV gp120-specific and only 12% (2/17) were platelet crossreactive. Western blot analysis of platelets demonstrated that the anti-p24 antibodies recognized three bands with approximate molecular weights of 72000 to 95000. 69% of the serum antiplatelet antibodies showed platelet glycoprotein IIbIIIa specificity. Anti-HIV antibodies could be eluted from platelets. Hence, platelet crossreactive antibodies in HIV infection are primarily alkaline-sensitive and are associated predominantly with HIV p24 antibody; these antibodies may play a role in the immune thrombocytopenia of HIV-infected haemophiliacs.

Overproduction, purification, and diagnostic use of the recombinant HIV-1 Gag proteins, the precursor protein p55 and the processed products p17, p24, and p15

HIV-1 Gag protein precursor p55, and its processed products, p17, p24, and p15 were overproduced in Escherichia coli and purified to near homogeneity. To study the antigenic properties and the potentiality as the diagnostic and prognostic reagents, varying amounts of the purified Gag proteins were dotted onto the polyvinylidene difluoride membrane and reacted with 40 sera of HIV-1-infected individuals (35 AC, 1 ARC, and 4 AIDS patients) and 10 sera of normal healthy donors. p55 reacted with 40 (100%) sera of HIV-1 carriers, while p17, p24, and p15 reacted with 37 (92.5%), 35 (87.5%) and 34 (85%) of the 40 sera of HIV-1 carriers, respectively. On the whole, the reaction of p55 was especially strong and that of p15 was the weakest. p55 showed the strongest reaction among the four Gag proteins with all specimens, and it showed a positive reaction with a carrier serum with which none of the processed Gag proteins showed a positive reaction. Therefore, p55 is the most useful antigen among the four Gag proteins for detection of the Gag antibodies and may even be one of the most useful antigens for the diagnosis of HIV-1 infection.

Loss of Gag-specific antibody reactivity in cattle experimentally infected with bovine immunodeficiency-like virus

The development and persistence of virus-specific antibodies were investigated in eight cattle experimentally infected with the R29 isolate of bovine immunodeficiency-like virus (BIV). By 4 weeks postinoculation (p.i.), antibodies reactive to BIV gag- and env-encoded recombinant fusion proteins were detectable by immunoblotting in all animals. By 40 weeks p.i., seven of eight cattle had dramatically decreased Gag-specific antibodies, and anti-Gag reactivity remained very low or undetectable through 190 weeks p.i. Immunoprecipitation experiments revealed a similar loss of reactivity to nondenatured BIV Gag in these animals. In contrast, antibodies to a recombinant BIV Env protein were readily detectable throughout the study in all eight cattle. During the period of declining Gag antibody, infectious virus was recoverable from peripheral blood mononuclear cells of each animal. However, there was no evidence for sufficient amounts of BIV p26-containing immune complexes to explain the loss of anti-Gag reactivity. Interestingly, the single animal that maintained detectable anti-Gag reactivity throughout the study was repeatedly negative for virus recovery beyond 17 weeks p.i. All animals have remained clinically normal for over 4 years p.i., with no evidence of consistent changes in mononuclear cell subsets. These findings provide evidence that in BIV infection an early decline in Gag-specific antibody reactivity can occur without evidence of increasing viral replication or progression to overt clinical disease.

Markers predicting progression of human immunodeficiency virus-related disease

Human immunodeficiency virus (HIV) interacts with the immune system throughout the course of infection. For most of the disease process, HIV activates the immune system, and the degree of activation can be assessed by measuring serum levels of molecules such as beta 2-microglobulin and neopterin, as well as other serum and cell surface phenotype markers. The levels of some of these markers correlate with clinical progression of HIV disease, and these markers may be useful as surrogate markers for development of clinical AIDS. Because the likelihood and timing of development of clinical AIDS following seroconversion, for any particular individual, are not readily predictable, the use of nonclinical disease markers has become critically important to patient management. Surrogate markers of HIV infection are, by definition, measurable traits that correlate with disease progression. An ideal marker should identify patients at highest risk of disease progression, provide information on how long an individual has been infected, help in staging HIV disease, predict development of opportunistic infections associated with AIDS, monitor the therapeutic efficacy of immunomodulating or antiviral treatments, and the easily quantifiable, reliable, clinically available, and affordable. This review examines the current state of knowledge and the role of surrogate markers in the natural history and treatment of HIV infection. The clinical usefulness of each marker is assessed with respect to the criteria outlined for the ideal surrogate marker for HIV disease progression.

Analysis of antibody response to ovine lentivirus by using viral gene products expressed in a prokaryotic system

The polymerase chain reaction (PCR) was used to amplify, clone, and express eight DNA fragments encoding p25, p16, reverse transcriptase (RT) core, C'-terminal RT, N'- and C'-terminals of external (gp70), and transmembrane (gp40) envelope proteins from visna virus infectious recombinant DNA. Efforts were focused on characterizing the nature of the humoral immune response of ovine progressive pneumonia (OPP) virus infected animals and identifying the conserved and prime-reactive antigenic determinants that have potential diagnostic value. This communication reports that the N'-terminal region of gp40 appeared to be the most immunoreactive of the bacterially expressed proteins and could serve as a sensitive immunodiagnostic antigen for the detection of OPP infection.

Quantitation of antibody reactivity to human immunodeficiency virus (type 1) proteins and glycoproteins on Western immunoblots by reflectance densitometry

The human serum antibody response to polypeptides of human immunodeficiency virus type 1 (HIV-1) was quantitated by reflectance densitometry of Western immunoblots by using two commercially available blotting systems. In one system, human antibodies were detected by an avidin-biotin method using peroxidase as the label, and in the other, human antibodies were detected by peroxidase-labeled conjugate against human immunoglobulins. When staining intensity was plotted against the log of the serum dilution, a shallow slope was evident, with a 50% change in staining intensity requiring as much as a 100-fold change in antibody content. The linear range of the staining intensity curves was frequently found in serum dilutions of 1:2,500 to 1:1,000,000, and a plateau was often observed at high antibody concentrations (1:80 to 1:640). When replicate strips were tested, staining intensities varied by +/- 7 to 37%. Antibodies to p24gag and gp160env were readily detectable in several sera diluted 1:1,000,000, a result seen with both blotting systems. If Western blotting were to be used to observe increase or decreases in levels of antibodies to various polypeptides, several widely spaced serum dilutions would need to be tested.

HGP-30, a synthetic analogue of human immunodeficiency virus (HIV) p17, is a target for cytotoxic lymphocytes in HIV-infected individuals

Evaluation of the immune response of individuals exposed to human immunodeficiency virus (HIV) is an important component of any plan designed to lead toward the development of an AIDS vaccine. Since the levels of antibodies to HIV p17 and the synthetic p17 peptide HGP-30 correlate with stages of progression to AIDS, studies were initiated to determine whether cytotoxic lymphocytes directed toward target cells pulsed with HGP-30 and radioactive chromium were present in seropositive individuals. The significance of such cells in controlling HIV viral infection has recently been enhanced by reports that HIV p17 is on the surface of infected cells and that an inactivated virus vaccine depleted of viral envelope appears to be effective in controlling expression. The selection of HGP-30 as the p17 peptide to be evaluated in early studies is based on the presence of both T-cell and B-cell epitopes as predicted by computer modeling and mouse studies and the demonstration of in vitro neutralization activity by antibodies to the epitope. By using B-lymphoblastoid cells pulsed with HGP-30 and radioactive chromium as autologous targets and mixed leukocyte culture-expanded peripheral blood lymphocytes as effectors, CD8+ cytotoxic T lymphocytes against HGP-30-coated targets were identified in seropositive individuals. In this report we demonstrate that a synthetic p17 epitope can be a target for major histocompatibility complex-restricted cytotoxic T lymphocytes in HIV-infected individuals.

Detection and quantitation of human immunodeficiency virus-infected peripheral blood mononuclear cells by flow cytometry

A flow cytometric assay has been developed to detect and quantitate human immunodeficiency virus (HIV)-infected peripheral blood mononuclear cells obtained from HIV-seropositive patients. Peripheral blood was obtained from patients attending an acquired immune deficiency syndrome clinic, and mononuclear cells were separated by centrifugation onto Ficoll-Hypaque. The cell layer at the interface was removed, washed in phosphate-buffered saline without Ca2+ and Mg2+, and fixed with 90% methanol, and intracellular HIV antigens were detected by indirect immunofluorescence with monoclonal antibodies to HIV antigens as the primary antibody and fluorescein isothiocyanate-conjugated goat anti-mouse immunoglobulin G F(ab')2 antibody as the secondary antibody. DNA content was determined by propidium diiodide staining after RNase treatment. These fluorochrome-treated cells were analyzed for two-color fluorescence by flow cytometry. The results showed that HIV-infected cells in peripheral blood that have been treated with monoclonal antibodies to the p24 or nef antigens of HIV can be detected and quantitated by flow cytometry. The percentage of p24 antigen-positive mononuclear cells had a significant correlation (P = 0.0001) with the clinical status of the patient, i.e., those with a high percentage of p24 antigen-positive cells had a poorer prognosis than those with a lower percentage of p24 antigen-positive mononuclear cells. In addition, for those in Centers for Disease Control groups III and IV, there was an inverse correlation between the percentage of p24 antigen-positive mononuclear cells and the number of T4 cells. However, cell-associated antigen detection by flow cytometry did not correlate with detection of antigen in sera of HIV-seropositive patients by the standard antigen capture enzyme-linked immunosorbent assay. This lack of correlation was probably due to the presence of immune complexes in the sera of HIV-seropositive patients. These results suggest that flow cytometry can be used as a rapid, sensitive, and quantitative assay system for the determination of the antigen status of HIV-seropositive patients and that it may be more useful as an indicator of disease progression than the currently used antigen detection methods.

Prognostic significance of quantitative levels of HIV p24 binding capacity in HIV infection

Human immunodeficiency virus, type 1 (HIV-1), produces a chronic infection with a long latency before clinical disease. We followed 214 untreated subjects for 12-42 months to study the natural history of HIV infection: 110 were classified as asymptomatic, 11 as AIDS-related complex (ARC), 15 as AIDS with Kaposi's sarcoma (KS), 31 as AIDS with opportunistic infections (AIDS/OI), and 47 were HIV-seronegative controls. The quantitative capacity of serum to complex HIV p24 antigen, termed the p24 binding capacity (p24 BC), and quantitative levels of HIV p24 antigen in serum were determined at regular intervals. For people in all diagnostic groups, a p24 BC below 31 ng/ml was more closely associated with progression to AIDS/OI than was p24 antigen positivity; 94% of AIDS/OI, 86% of ARC, 56% of AIDS/KS, and 19% of asymptomatic subjects had p24 BC less than 31 ng/ml during the study period, while 67% of AIDS/OI, 27% of ARC, 61% of AIDS/KS, and 20% of asymptomatic subjects were p24 antigenemic. Prospective analysis of 47 asymptomatic seropositive men followed for 3 years, who showed actuarial progression rates to ARC at 4%, 13%, and 23% and to AIDS at 5%, 8%, and 8% at 1, 2, and 3 years, indicated that entry levels of p24 BC below 31 ng/ml were as strongly associated with progression to ARC/AIDS as was p24 antigenemia (p = 0.0003 vs. p = 0.008). The p24 binding capacity assay is a new and convenient methodology to measure immunocomplexing antibody to HIV p24 and is a powerful indicator of progressive HIV disease.

Prevalence of antibodies to the core protein P17, a serological marker during HIV-1 infection

Studies on monitoring the immune response to viral structural proteins during human immunodeficiency virus (HIV-1) infection have established the significance of antibodies to the core protein p24 during the progression of the disease. We have studied the prevalence of antibodies to the core protein p17 in order to study their diagnostic and prognostic significance in the pathogenesis of HIV-1. Full-length HIV-1 p17, molecularly cloned and expressed in Escherichia coli was purified by immunoaffinity chromatography using an HIV-1 p17-specific monoclonal antibody. A highly sensitive enzyme-linked immunoassay was developed using the purified recombinant p17 as the serological target to detect antibodies to p17. The results indicated that antibodies to p17 decline during progression of disease, with the decline being more dramatic as patients moved from asymptomatic to AIDS-related complex (ARC). Patient specimens deficient in p24 antibody, but having detectable levels of antibody to p17 were almost always positive for p24 antigen. Under these conditions, p17 antibody is an important serological marker because it provides a more consistent marker for core antigens during HIV-1 infection.

Comparison of different methods for detecting human immune deficiency virus in human immunodeficiency virus-seropositive hemophiliacs

Since the detection of antibodies against the human immune deficiency virus (HIV) does not definitely prove HIV infection in hemophiliacs, virus detection was attempted by virus isolation from the peripheral blood monocytes (PBL), by demonstration of p24 antigen and decline of p24 antibody, and by detection of viral DNA by the polymerase chain reaction (PCR). Virus isolation was optimized by immediate coculture of PBL and by replacement of the reverse transcriptase test by the p24 antigen test, whereas the elimination of CD8+ lymphocytes proved to be unnecessary. Virus detection was dependent on the clinical stage of the illness. Virus isolation in 70 of 211 patients (33%) was more sensitive than detection of p24 antigen or decline of p24 antibody. PCR was performed in 25 patients and indicated infection in all of 15 isolation-positive cases and in 6 of 10 patients from whom virus was not isolated. Changes from negative to positive virus culture and from a weakly fusiogenic to a highly fusiogenic isolate were often accompanied by a progression of the disease. The results suggest that reactivation of HIV occurs when immune deficiency has become manifest. Apparently virus isolation detects only the virus already reactivated in vivo, whereas the PCR may also detect latent virus.