Induction of interleukin-10 by human immunodeficiency virus type 1 and its gp120 protein in human monocytes/macrophages.

In this study, we evaluated the effects of human immunodeficiency virus type 1 (HIV-1) and its gp120 protein on interleukin-10 (IL-10) expression in cultured human monocytes/macrophages. Infection of either 1-day monocytes or 7-day monocyte-derived macrophages with HIV-1 strain Ba-L resulted in clear-cut accumulation of IL-10 mRNA at 4 and 24 h. Likewise, treatment of these cells with recombinant gp120 induced IL-10 mRNA expression and caused a marked increase in IL-10 secretion. Monoclonal antibodies to gp120 strongly inhibited recombinant gp120-induced IL-10 secretion by monocytes/macrophages. Moreover, the addition of IL-10 to monocytes/macrophages resulted in a significant inhibition of HIV-1 replication 7 and 14 days after infection. On the whole, these results indicate that HIV-1 (possibly through its gp120 protein) up-regulates IL-10 expression in monocytes/macrophages. We suggest that in vivo production of IL-10 by HIV-primed monocytes/macrophages can play an important role in the early response to HIV-1 infection.     

Directional budding of human immunodeficiency virus from monocytes.

Time-lapse cinematography revealed that activated human immunodeficiency virus (HIV)-infected monocytes crawl along surfaces, putting forward a leading pseudopod. Scanning electron micrographs showed monocyte pseudopods associated with spherical structures the size of HIV virions, and transmission electron micrographs revealed HIV virions budding from pseudopods. Filamentous actin (F-actin) was localized by electron microscopy in the pseudopod by heavy meromyosin decoration. Colocalization of F-actin and p24 viral antigen by light microscopy immunofluorescence indicated that F-actin and virus were present on the same pseudopod. These observations indicate that monocytes produce virus from a leading pseudopod. We suggest that HIV secretion at the leading edges of donor monocytes/macrophages may be an efficient way for HIV to infect target cells.     

T-cell-induced expression of human immunodeficiency virus in macrophages

Macrophages are major reservoirs of human immunodeficiency virus (HIV) in the tissues of infected humans. As monocytes in the peripheral blood do not show high levels of infection, we have investigated the expression of HIV in T-cell-activated, differentiated macrophages. Peripheral blood mononuclear cells were isolated from HIV-seropositive individuals and stimulated with antigens or mitogens, and the nonadherent fraction was removed. Macrophages were cultured alone for 2 weeks, and HIV expression was assessed. Results from p24 antigen capture assays demonstrated that the presence of autologous T cells and concanavalin A or autologous T cells and allogeneic cells for the initial 24 h of culture induced HIV expression in 35 of 47 (74%) HIV-seropositive patients tested. The macrophage monolayers could be immunostained with anti-HIV antibodies to reveal discrete infectious centers, indicating that complete virus replication was occurring in the macrophages and that infection of adjacent cells was mediated by cell-cell contact. Time course studies of the interval of coculture of the adherent and nonadherent cells indicated that 24 h (but not 2 h) was sufficient for induction of HIV in the macrophages. Direct contact between the adherent cells and activated T cells was required as well. Since the presence of autologous T cells also appeared to be necessary, induction of HIV expression in macrophages may be genetically restricted. HIV-seronegative nonadherent cells were able to induce HIV expression in macrophages from HIV-seropositive donors, demonstrating that the virus originated in the monocytes and was reactivated in the context of a classic T-cell-mediated immune reaction. The high percentage of monocytes from HIV-seropositive donors which can be induced to replicate HIV by activated T cells suggests that infection of monocytes may be critical to the pathogenesis of this lentivirus infection.     

Twin studies demonstrate a host cell genetic effect on productive human immunodeficiency virus infection of human monocytes and macrophages in vitro.

Biological and genetic variability is a prominent feature of human immunodeficiency virus (HIV) strains, especially in tropism, syncytium formation, and replicative capacity. To determine whether there were variable host cell effects on HIV replication in monocytes, three different strains of low-passage-number monocytotropic blood isolates of HIV and the laboratory-adapted strain Ba-L were inoculated into panels of adherent monocytes drawn from 44 different donors, and peak extracellular HIV p24 antigen titers were compared. The clinical HIV strains showed patterns of either moderate or low-level replication in most donor monocytes (20 to 4,000 pg/ml). However, within this range there was marked variation in peak titers in most donors. HIV type 1 Ba-L replicated in all donor monocytes to much higher levels with less variability (30 to 40 ng/ml). Furthermore, replication of 21 clinical blood-derived strains of HIV in blood monocytes and monocyte-derived macrophages (MDM) from pairs of identical twins and age-matched unrelated donors (URD) of the same sex were compared. In all of the seven pairs of identical twins, the kinetics of replication (measured by extracellular HIV p24 antigen) of panels of four clinical HIV type 1 isolates in monocytes were similar within pairs. However, marked and significant differences in kinetics of HIV production occurred within 10 of the 12 unrelated donor pairs (P = 0.0007). The remaining two URD pairs showed similar kinetic patterns, but only one pair had the same HLA-DR genotype. Similar results were observed with monocytes/MDMs obtained from a second bleed of the same donor. Hence, discordant patterns of HIV replication kinetics between URD monocyte pairs contrasted with concordant patterns in identical twin monocytes. These data strongly suggest a host cell genetic effect on productive viral replication in monocytes and MDMs. So far, no consistent genetic linkage of HIV replication pattern with HLA-DR genotype has been observed.     

Mechanisms for adaptation of simian immunodeficiency virus to replication in alveolar macrophages

In contrast to the simian immunodeficiency virus SIVmac239, which replicates poorly in rhesus monkey alveolar macrophages, a variant with nine amino acid changes in envelope (SIVmac239/316E) replicates efficiently and to high titer in these same cells. We examined levels of viral DNA, RNA, antigen, and infectious virus to identify the nature of the block to SIVmac239 replication in these cells. Low levels of viral antigen (0.1 to 1.0 ng of p27 per ml) and infectious virus (100 to 1,000 infectious units per ml) were produced in the supernatant 1 to 4 days after SIVmac239 infection, but these levels did not increase subsequently. SIVmac239 DNA was synthesized in these macrophage cultures during the initial 24 h after infection, but the levels did not increase subsequently. Quantitation of the numbers of infectious cells in cultures over time and the results of experiments in which cells were reexposed to SIVmac239 after the initial exposure indicated that only a small proportion of cells were susceptible to SIVmac239 infection in these alveolar macrophage cultures and that the vast majority (>95%) of cells were refractory to SIVmac239 infection. In contrast to the results with SIVmac239, the levels of viral antigen, infectious virus, and viral DNA increased exponentially 2 to 7 days after infection by SIVmac239/316E, reaching levels greater than 100 ng of p27 per ml and 100,000 infectious units per ml. Since SIVmac239/316E has previously been described as a virus capable of infecting cells in a relatively CD4-independent fashion, we examined the levels of CD4 expression on the surface of fresh and cultured alveolar macrophages from rhesus monkeys. The levels of CD4 expression were extremely low, below the limit of detection by flow cytometry, on greater than 99% of the macrophages. CCR5(+) cells were profoundly depleted only from alveolar macrophage cultures infected with SIVmac239/316E. High concentrations of an antibody to CD4 delayed but did not block replication of SIVmac239/316E. The results suggest that the adaptation of SIVmac316 to efficient replication in alveolar macrophages results from its ability to infect these cells in a CD4-independent fashion or in a CD4-dependent fashion even at extremely low levels of surface CD4 expression. Since resident macrophages in brains and lungs of humans also express little or no CD4, our findings predict the presence of human immunodeficiency virus type 1 that is relatively CD4 independent in the lung and brain compartments of infected people.     

Complement activation by human monoclonal antibodies to human immunodeficiency virus.

It has been shown that the incubation of human immunodeficiency virus (HIV) with polyclonal antibodies from HIV-infected persons and complement results in complement-mediated neutralization due, at least in part, to virolysis. The current study was performed to determine whether any of a panel of 16 human monoclonal antibodies to HIV could activate complement and, if so, which determinants of the HIV envelope could serve as targets for antibody-dependent complement-mediated effects. Human monoclonal antibodies directed to the third variable region (V3 region) of HIVMN gp120 induced C3 deposition on infected cells and virolysis of free virus. Antibodies to two other sites on HIVMN gp120 and two sites on gp41 induced few or no complement-mediated effects. Similarly, only anti-V3 antibodies efficiently caused complement-mediated effects on the HIVIIIB isolate. In general, the level of C3 deposition on infected cells paralleled the relative level of bound monoclonal antibodies. As expected, pooled polyclonal antibodies from infected persons were much more efficient than monoclonal antibodies inducing C3 deposition per unit of bound immunoglobulin. Treatment of virus or infected cells with soluble CD4 resulted in increases in anti-gp41 antibody-mediated virolysis and C3 deposition but decreases in anti-V3 antibody-mediated virolysis and C3 deposition. In general, virolysis of HIV was more sensitive as an indicator of complement-mediated effects than infected-cell surface C3 deposition, suggesting the absence of or reduced expression of functional complement control proteins on the surface of free virus. Thus, this study shows that human monoclonal antibodies to the V3 region of gp120 are most efficient in causing virolysis of free virus and C3 deposition on infected cells. Elution of gp120 with soluble CD4 exposes epitopes on gp41 that can also bind antibody, resulting in virolysis and C3 deposition. These findings establish a serologically defined model system for the further study of the interaction of complement and HIV.     

Change in tropism upon immune escape by human immunodeficiency virus.

The V3 loop of human immunodeficiency virus type 1 is both a determinant of viral cell tropism and a target for neutralizing antibodies. This relationship was investigated. Selection of a dual-tropic (T cells and macrophages) virus to replicate in CD4+ brain cells results in loss of macrophage tropism and of neutralization by an anti-V3 loop monoclonal antibody. Moreover, selection of the brain-selected variant to escape from V3 loop-specific neutralizing monoclonal antibodies results in the reduction or loss of brain cell tropism and the reacquisition of macrophage tropism. These data may indicate that the antigenic diversification of human immunodeficiency virus type 1 apparent after seroconversion can be selected either by immune responses or by colonization of new cell types.     

CCR5 signal transduction in macrophages by human immunodeficiency virus and simian immunodeficiency virus envelopes

The capacity of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) envelopes to transduce signals through chemokine coreceptors on macrophages was examined by measuring the ability of recombinant envelope proteins to mobilize intracellular calcium stores. Both HIV and SIV envelopes mobilized calcium via interactions with CCR5. The kinetics of these responses were similar to those observed when macrophages were treated with MIP-1beta. Distinct differences in the capacity of envelopes to mediate calcium mobilization were observed. Envelopes derived from viruses capable of replicating in macrophages mobilized relatively high levels of calcium, while envelopes derived from viruses incapable of replicating in macrophages mobilized relatively low levels of calcium. The failure to efficiently mobilize calcium was not restricted to envelopes derived from CXCR4-utilizing isolates but also included envelopes derived from CCR5-utilizing isolates that fail to replicate in macrophages. We characterized one CCR5-utilizing isolate, 92MW959, which entered macrophages but failed to replicate. A recombinant envelope derived from this virus mobilized low levels of calcium. When macrophages were inoculated with 92MW959 in the presence of MIP-1alpha, viral replication was observed, indicating that a CC chemokine-mediated signal provided the necessary stimulus to allow the virus to complete its replication cycle. Although the role that envelope-CCR5 signal transduction plays in viral replication is not yet understood, it has been suggested that envelope-mediated signals facilitate early postfusion events in viral replication. The data presented here are consistent with this hypothesis and suggest that the differential capacity of viral envelopes to signal through CCR5 may influence their ability to replicate in macrophages.     

Multibranched V3 peptides inhibit human immunodeficiency virus infection in human lymphocytes and macrophages.

Synthetic polymeric constructions (SPCs) including the consensus sequence of the human immunodeficiency virus type 1 (HIV-1) surface envelope glycoprotein gp120 V3 loop (GPGRAF) blocked the fusion between HIV-1- and HIV-2-infected cells and CD4+ uninfected cells. A structure-activity relationship study using V3 SPC analogs showed that the most efficient inhibitor of cell fusion was an eight-branched SPC with the hexapeptide motif GPGRAF (i.e., [GPGRAF]8-SPC). N-terminal acetylation or incorporation of D-amino acids in the GPGRAF sequence of this SPC resulted in significant loss of activity. Analogs with fewer than six residues in the motif (i.e., GPGRA or GPGR), as well as SPCs with a nonrelevant sequence, did not inhibit cell fusion, demonstrating the high specificity of the antifusion activity. [GPGRAF]8-SPC, which was not toxic to CEM cells at concentrations of up to 50 microM, inhibited 50% of HIV-1(LAI) replication in these cells at a concentration of 0.07 microM. Moreover, [GPGRAF]8-SPC inhibited the infection of human peripheral blood mononuclear cells by several HIV-1 and HIV-2 isolates, including laboratory strains [HIV-1(LAI), HIV-1(NDK), and HIV-2(ROD)], and fresh primary isolates, including two zidovudine-resistant HIV-1 isolates and two HIV-2 isolates obtained from infected individuals. The multibranched peptide also inhibited infection of human primary macrophages by the highly cytopathic macrophage-tropic isolate HIV-1(89.6). The antiviral activity of [GPGRAF]8-SPC was not related to a virucidal effect, since preincubation of HIV-1 with the peptide did not affect its infectious titer. This result is in agreement with the concept that the multibranched peptide mimics a part of the V3 loop and thus interacts with the host cell. The therapeutic properties of synthetic multibranched peptides based on the V3 loop consensus motif should be evaluated in HIV-infected patients.     

UV activation of human immunodeficiency virus gene expression in transgenic mice.

Human immunodeficiency virus (HIV) infection is associated with a clinical latency of as long as 10 years before the development of disease. One explanation for this delay is the requirement of cofactors such as other DNA or RNA viruses, cytokines critical for immune modulation, or environmental UV light. At least in tissue culture studies, these agents are capable of inducing HIV gene expression in cell lines which either harbor the entire viral genome or contain a reporter gene under the control of the viral long terminal repeat regulatory region. The role of these cofactors in terminating clinical latency and inducing disease has been difficult to ascertain because of the lack of an appropriate animal model. We now report that UV light can markedly induce HIV gene expression in transgenic mice carrying both the cis-acting (long terminal repeat) and trans-acting (the tat gene) elements which are essential for viral transactivation and replication in infected cells. Our finding may explain the clinical observations that cutaneous lesions in HIV-infected individuals are often seen in the sunlight exposed areas of the skin, including the face and neck.     

Nitric oxide synthesis enhances human immunodeficiency virus replication in primary human macrophages

Macrophages are suspected to play a major role in human immunodeficiency virus (HIV) infection pathogenesis, not only by their contribution to virus dissemination and persistence in the host but also through the dysregulation of immune functions. The production of NO, a highly reactive free radical, is thought to act as an important component of the host immune response in several viral infections. The aim of this study was to evaluate the effects of HIV type 1 (HIV-1) Ba-L replication on inducible nitric oxide synthase (iNOS) mRNA expression in primary cultures of human monocyte-derived macrophages (MDM) and then examine the effects of NO production on the level of HIV-1 replication. Significant induction of the iNOS gene was observed in cultured MDM concomitantly with the peak of virus replication. However, this induction was not accompanied by a measurable production of NO, suggesting a weak synthesis of NO. Surprisingly, exposure to low concentrations of a NO-generating compound (sodium nitroprusside) and L-arginine, the natural substrate of iNOS, results in a significant increase in HIV replication. Accordingly, reduction of L-arginine bioavailability after addition of arginase to the medium significantly reduced HIV replication. The specific involvement of NO was further demonstrated by a dose-dependent inhibition of viral replication that was observed in infected macrophages exposed to N(G)-monomethyl L-arginine and N(G)-nitro-L-arginine methyl ester (L-NAME), two inhibitors of the iNOS. Moreover, an excess of L-arginine reversed the addition of L-NAME, confirming that an arginine-dependent mechanism is involved. Finally, inhibitory effects of hemoglobin which can trap free NO in culture supernatants and in biological fluids in vivo confirmed that endogenously produced NO could interfere with HIV replication in human macrophages.