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A colinearly synthesized peptide consisting of a H-2d restricted T-helper cell epitope of Semliki Forest virus (SFV) and triple repeats of sequence GPGRAF, derived from the V3 domain of HIV-1 strains, was used to immunize BALB/c (H-2d) mice. Pepscan analysis of sera from peptide-immunized mice revealed that the chimaeric peptide GREKFTIRPHYGKEIGPGRAFGPGRAFGPGRAF contains three distinct antibody-reactive sequences GREKFTIR, PHYGKEI and GPGRAF. The chimaeric peptide evoked HIV-1 IIIb neutralizing antibodies in serum as measured in vitro by reduction of syncytia formation and reduction of p24 production as well. So, the T-helper cell epitope of SFV provided help to a small linear neutralization epitope of HIV-1 strains. Interestingly, the T-helper cell epitope alone might induce antibodies cross-reactive with HIV-1 IIIb specific peptide GPGRAFVTIGK which shows some homology (residues underlined) with the antibody-reactive sequence GREKTIR of SFV.

The relationship between T cell activation and human immunodeficiency virus type 1 (HIV-1) replication was studied in HIV-infected subjects, 20 with and 10 without anti-HIV treatment. Expression of Ki-67 proliferation-associated antigen was increased in CD4+ and CD8+ T cells and correlated with HLA-DR. In subjects without anti-HIV treatment, the plasma HIV-1 RNA level correlated with HLA-DR in CD4+ T cells, with Ki-67 in CD8+ T cells, and with expression of CD38 in both T cell subsets. A proportion of treated subjects had increased T cell activation despite 4 months of highly active antiretroviral treatment (HAART). In subjects receiving HAART, a high percentage of HLA-DR+ CD4+ T cells was associated with signs of opportunistic infections. This work supports the concept that, in the natural course of HIV-1 infection, HIV replication itself leads to general T cell activation and that opportunistic infections generate additional CD4+ T cell activation and HIV replication.

To investigate the effects of Mycobacterium tuberculosis on HIV-1 replication, peripheral blood mononuclear cells (PBMC) of bacille Calmette-Guerin (BCG)-vaccinated donors and non-BCG-vaccinated donors were infected in vitro with a lymphotropic isolate of HIV-1 and cultured in the presence of purified protein derivative (PPD). Addition of PPD resulted in enhanced HIV-1 replication and lymphoproliferation in BCG-vaccinated donor PBMC, while PPD had no such effects in control PBMC. HIV-1 replication increased even more when monocytes were removed from PBMC, while lymphoproliferation was decreased. High percentages of monocytes were associated with a decreased HIV-1 replication and proliferation that could not be reversed by addition of antibodies against the cytokines IL-1, transforming growth factor-beta (TGF-beta) or indomethacin. PPD stimulates PBMC to release IL-10, a cytokine known to down-regulate proliferation and HIV-1 replication. PPD-induced effects on proliferation as well as HIV-1 replication could be partially blocked by adding a monoclonal antibody against MHC class II molecules, suggesting that part of the mechanism of PPD-induced enhancement is T memory cell activation.

To investigate the possible role of Cryptococcus neoformans var. neoformans in HIV disease progression, and to identify the responsible cryptococcal components, an in vitro cell culture model was set up to study the C. neoformans-induced enhancement of HIV replication in HIV-1-infected PBMC. Similar to whole C. neoformans, cell-wall membrane fraction and mannoproteins induced proliferation of PBMC and enhancement of lymphotropic HIV replication in HIV-infected PBMC, while galactoxylomannan did not. MoAbs capable of interfering with MHC class II-mediated antigen presentation prevented the induction of cell proliferation by whole C. neoformans or cryptococcal mannoproteins. MoAb binding to adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1) also inhibited C. neoformans-induced cell proliferation. In addition, anti-MHC class II MoAb inhibited the enhancement of HIV replication by C. neoformans. The results suggest that: (i) C. neoformans may accelerate HIV disease progression by stimulation of HIV replication through MHC class II-mediated antigen presentation; and (ii) cryptococcal mannoprotein may be one of the responsible components. The ability to enhance HIV replication in PBMC in vitro is not unique for C. neoformans. However, this is the first report to study in detail a yeast-induced enhancement of HIV replication in PBMC.

Nuclear factor kappaB (NF-kappaB) is an important cellular regulator of human immunodeficiency virus (HIV) gene expression. In T cells, N-acetyl-L-cysteine (NAC) inhibits the induction of NF-kappaB and transcription of HIV-1. However, NAC up-regulates HIV-1 replication in monocyte-derived macrophages (MDM). In this study we demonstrate that NAC treatment of MDM transfected with a chloramphenicol acetyltransferase (CAT) construct under transcriptional control of the HIV-1 long terminal repeat resulted in an up-regulation of CAT activity. Furthermore, MDM transfected with a HIV-1-NF-kappaB-CAT construct also produced increased CAT activity after NAC treatment. In addition, electrophoretic mobility shift assays revealed that nuclei of NAC-treated MDM contained increased binding activity to wild-type, but not mutant, kappaB oligonucleotides. Components of the binding activity were identified with antibodies as the NF-kappaB subunits p50 and p65. These data indicate that NAC-induced enhancement of HIV-1 replication in MDM is regulated at the level of viral gene expression and mediated by NF-kappaB.

N-acetyl-L-cysteine (NAC) has been proposed as a therapeutic agent for AIDS patients because it reduces human immunodeficiency virus type 1 (HIV-1) replication in stimulated T cells. However, NAC and glutathione enhanced acute HIV-1 replication in monocyte-derived macrophages. Buthionine sulfoximine did not affect NAC-mediated enhanced HIV-1 replication, indicating that the NAC-mediated effects are glutathione-independent. Superoxide dismutase and the hydroxyl radical scavengers dimethylthiourea and thiourea, but not urea, inhibited acute HIV-1 replication in macrophages. NAC reduced ferricytochrome c and increased dose-dependently Fe(III)-citrate and Fe(III)-EDTA-catalyzed hydroxyl radical formation in a system using glucose and glucose oxidase. Dimethylthiourea and thiourea, but not urea and superoxide dismutase, dose-dependently inhibited NAC-mediated enhancement of HIV-1 replication. These data suggest that oxygen radicals play an important role in self-sustained HIV-1 replication in macrophages and that oxygen radical scavengers other than NAC should be considered as therapeutic agents for AIDS patients.

The immunopathogenesis of human immunodeficiency virus (HIV) infection is characterized by the failure to control opportunistic infections. Here, the direct effect of HIV on macrophage phagocytic function was studied. HIV-1-infected monocyte-derived macrophages expressed as many Fc gamma and complement receptors as did control macrophages. The function of these receptors was not affected by HIV-1 infection since binding and internalization of opsonized Escherichia coli and Staphylococcus aureus were not impaired. Production of reactive oxygen species induced by stimulation of the HIV-1-infected macrophages with opsonized E. coli, zymosan, or PMA was intact. HIV-1-infected macrophages killed opsonized E. coli and Candida albicans as effectively as did control macrophages. These results, therefore, do not support the hypothesis that HIV-1 infection of macrophages causes phagocytic dysfunction and suggest that HIV-induced abnormalities outside the mononuclear phagocyte system may lead to the inability to control opportunistic pathogens.

Low levels of anti-viral antibodies may facilitate virus infection of Fc-receptor bearing cells. For human immunodeficiency virus (HIV) it has been reported that antibodies can enhance infection of phagocytic cells. We show that HIV-1 can infect an Epstein-Barr virus transformed B cell line and that low levels of anti-HIV antibodies enhance infection. The enhanced infection was characterized by an increase in viral DNA and increased HIV p24 protein production. Detection of cell surface antigen expression of CD4, the receptor for HIV, Fc-receptor type II for IgG, but not of type I and III could be demonstrated by immunofluorescence cytometry. The enhancement was abrogated when infection was performed in presence of a monoclonal antibody directed against CD4. Based on these results we conclude that antibody mediated enhancement of HIV-1 infection can also occur in non-phagocytic cells in a CD4 dependent manner and that IgG Fc-receptors other than types I or III are involved in this process.

Objective: To characterize antibody- and complement-mediated binding and uptake of HIV-1 by human monocytes., Design: The first step in the infection of the monocyte by HIV-1 is binding of the virus to the susceptible cell. Procedures were designed to assess the influence of anti-HIV-1 antibodies and complement on this binding, and to study the process of internalization following binding., Methods: Human monocytes were incubated with fluorescein-labelled purified HTLV-IIIB virions and human sera with high-titre anti-HIV-1 antibodies and/or complement. Binding and uptake of virus by the monocytes was measured as fluorescence per cell by flow cytometry., Results: Binding of purified HIV-1 to monocytes was increased by complement and, to a lesser extent, by anti-HIV-1 antibodies. Uptake of HIV-1 bound to the monocyte appeared to be mediated by antibodies and was increased further by the presence of complement. Complement alone, however, resulted in the uptake of only a small part of the bound virus., Conclusions: Complement significantly increases the binding of HIV-1 to human monocytes, and a combination of antibodies and complement efficiently mediates uptake of HIV-1 by monocytes.