Induction of apoptosis by primary HIV-1 isolates correlates with productive infection in peripheral blood mononuclear cells

Dissecting How CD4 T Cells Are Lost During HIV Infection

Although the replicative life cycle of HIV within CD4 T cells is understood in molecular detail, less is known about how this human retrovirus promotes the loss of CD4 T lymphocytes. It is this cell death process that drives clinical progression to acquired immune deficiency syndrome (AIDS). Recent studies have highlighted how abortive infection of resting and thus nonpermissive CD4 T cells in lymphoid tissues triggers a lethal innate immune response against the incomplete DNA products generated by inefficient viral reverse transcription in these cells. Sensing of these DNA fragments results in pyroptosis, a highly inflammatory form of programmed cell death, that potentially further perpetuates chronic inflammation and immune activation. As discussed here, these studies cast CD4 T cell death during HIV infection in a different light. Further, they identify drug targets that may be exploited to both block CD4 T cell demise and the chronic inflammatory response generated during pyroptosis.

Elevated levels of macrophage migration inhibitory factor (MIF) in the plasma of HIV-1-infected patients and in HIV-1-infected cell cultures: a relevant role on viral replication

The cytokine macrophage migration inhibitory factor (MIF) is involved in the pathogenesis of inflammatory and infectious diseases, however its role in HIV-1 infection is unknown. Here we show that HIV-1-infected patients present elevated plasma levels of MIF, that HIV-1-infected peripheral blood mononuclear cells (PBMCs) release a greater amount of MIF, and that the HIV-1 envelope glycoprotein gp120 induces MIF secretion from uninfected PBMCs. The HIV-1 replication in PBMCs declines when these cells are treated with anti-MIF antibodies, and exposure of HIV-1-infected cells to the ABC-transporter inhibitor probenecid results in inhibition of MIF secretion. The addition of recombinant MIF (rhMIF) to HIV-1-infected PBMCs enhances viral replication of CCR5- or CXCR4-tropic HIV-1 isolates. Using a T CD4(+) cell lineage containing an HIV long terminal repeats (LTR)-Luciferase construct, we detected that rhMIF promotes transcription from HIV-1 LTR. Our results show that HIV-1 induces MIF secretion and suggest that MIF influences the HIV-1 biology through activation of HIV-1 LTR.

Vpr cytopathicity independent of G2/M cell cycle arrest in human immunodeficiency virus type 1-infected CD4+ T cells

The mechanism of CD4(+) T-cell depletion in human immunodeficiency virus type 1 (HIV-1)-infected individuals remains unknown, although mounting evidence suggests that direct viral cytopathicity contributes to this loss. The HIV-1 Vpr accessory protein causes cell death and arrests cells in the G(2)/M phase; however, the molecular mechanism underlying these properties is not clear. Mutation of hydrophobic residues on the surface of its third alpha-helix disrupted Vpr toxicity, G(2)/M arrest induction, nuclear localization, and self-association, implicating this region in multiple Vpr functions. Cytopathicity by virion-delivered mutant Vpr protein correlated with G(2)/M arrest induction but not nuclear localization or self-association. However, infection with whole virus encoding these Vpr mutants did not abrogate HIV-1-induced cell killing. Rather, mutant Vpr proteins that are impaired for G(2)/M block still prevented infected cell proliferation, and this property correlated with the death of infected cells. Chemical agents that inhibit infected cells from entering G(2)/M also did not reduce HIV-1 cytopathicity. Combined, these data implicate Vpr in HIV-1 killing through a mechanism involving inhibiting cell division but not necessarily in G(2)/M. Thus, the hydrophobic region of the third alpha-helix of Vpr is crucial for mediating G(2)/M arrest, nuclear localization, and self-association but dispensable for HIV-1 cytopathicity due to residual cell proliferation blockade mediated by a separate region of the protein.

Apoptosis induced in synchronized human immunodeficiency virus type 1-infected primary peripheral blood mononuclear cells is detected after the peak of CD4+ T-lymphocyte loss and is dependent on the tropism of the gp120 envelope glycoprotein

Disease progression in human immunodeficiency virus type-1 (HIV-1)-infected individuals is frequently accompanied by declining CD4 cell numbers and the acquisition of a T-tropic (X4) or dual tropic (R5X4) phenotype. Understanding the mechanism of CD4 cell loss in HIV-1 infection is essential for the development of effective therapeutic strategies. In this study, donor populations of peripheral blood mononuclear cells (PBMCs) were selected for their ability to support an equivalent acute infection by both R5 and X4 virus phenotypes. This demonstrated that CD4+ T-lymphocyte loss was due to the gp120 region of Env and was replication independent. Furthermore, apoptosis was only detected in cells infected with an X4 virus after the majority of CD4+ T-lymphocyte loss had occurred. These observations indicate that the CD4+ T-lymphocyte loss in an X4 HIV-1 infection is not directly mediated by apoptosis, although apoptosis may be induced in the remaining cell population as a consequence of this CD4+ T-lymphocyte loss.

The varicella-zoster virus induces apoptosis in vitro in subpopulations of primary human peripheral blood mononuclear cells

Varicella-zoster virus (VZV), a member of Herpesviridae, subfamily alpha-Herpesvirinae, is pathogenic exclusively in the human. Chickenpox is the result of primary infection of VZV. During the viremic stage, VZV infects peripheral blood mononuclear cells (PBMC) and spreads to the periphery. In skin cells it causes typical lesions. Apoptosis has been demonstrated in different cell types by other alpha-herpesviruses. VZV-infected T lymphocytes, B lymphocytes, and monocytes, respectively, were examined in this in vitro study by flow cytometry, immunofluorescence and electron microscopy. All infected cell types showed signs of apoptosis: a lower DNA content, DNA fragmentation, loss of membrane integrity, and an altered nuclear morphology. The results observed led to the suggestion that VZV can induce apoptosis during infection in vivo in the PBMC subpopulations.

Role of nitric oxide in HIV-1 infection: friend or foe?

Nitric oxide (NO) is an important biologically active molecule that plays a key part in host defence against bacteria, protozoa, and tumour cells. NO has antiviral effects against several DNA viruses, such as murine poxvirus, herpes simplex virus, and Epstein-Barr virus, and some RNA viruses, such as coxsackievirus. In several studies, in vitro and in vivo, overproduction of NO has been noted in the presence of HIV-1 infection. Furthermore, increased NO production may contribute directly to the pathogenesis of HIV-1-associated dementia. The mechanisms of virus infection mediated by NO may be related to: direct antiviral effects of NO; impairment of antiviral defence mediated by T-helper-1 immune response by suppressing T-helper-1 functions; NO-induced cytotoxic effects by oxidative injury with cellular and organ dysfunctions; and NO-induced oxidative stress leading to rapid viral evolution with productions of drug-resistant and immunologically tolerant mutants. By contrast, there is some evidence of NO activity--directly, indirectly, or both--decreasing or blocking HIV-1 replication, through inhibition of viral enzymes, such as reverse transcriptase, protease, or cellular nuclear transcription factor (NF-kappa B) and long-terminal repeat-driven transcription. Therefore, although NO surely plays an important part in HIV-1 infection, that role is sometimes helpful and other times damaging to the host. Future challenges are to learn more about the beneficial and harmful effects of NO in HIV-1 infection, and how to selectively inhibit excessive NO production or to use NO-releasing drugs to decrease viral replication. This review discusses the role of NO in the pathogenesis of HIV-1 infection, inasmuch as its role against HIV-1 is unequivocal in inhibiting or increasing viral replication.

Cytopathic killing of peripheral blood CD4(+) T lymphocytes by human immunodeficiency virus type 1 appears necrotic rather than apoptotic and does not require env

An important unresolved issue of AIDS pathogenesis is the mechanism of human immunodeficiency virus (HIV)-induced CD4(+) T-lymphocyte destruction. We show here that HIV type 1 (HIV-1) exerts a profound cytopathic effect upon peripheral blood CD4(+) T lymphocytes that resembles necrosis rather than apoptosis. Necrotic cytopathology was found with both laboratory-adapted strains and primary isolates of HIV-1. We carefully investigated the role of env, which has been previously implicated in HIV cytopathicity. HIV-1 stocks with equivalent infectivity were prepared from constructs with either an intact or mutated env coding region and pseudotyped with the glycoprotein of vesicular stomatitis virus (VSV-G) so that the HIV envelope was not rate-limiting for infection. Infected Jurkat T cells died whether or not env was intact; however, the expression of env accelerated death significantly. The accelerated death was blocked by protease inhibitors, indicating that it was due to reinfection by newly produced virus in env(+) cultures. Accordingly, we found no disparity in kinetics in CD4(lo) Jurkat cells. In highly infected peripheral blood T cells, profound necrosis occurred equivalently with both env(+) and env(-) stocks of HIV-1. We also found that HIV-1 cytopathicity was undiminished by the absence of nef. However, viral stocks made by complementation or packaging of HIV-1 genomes with the natural protein-coding sequences replaced by the green fluorescent protein were highly infectious but not cytopathic. Thus, env can accelerate cell death chiefly as an entry function, but one or more viral functions other than env or nef is essential for necrosis of CD4(+) T cells induced by HIV-1.

Apoptosis induced by in vitro infection with simian-human immunodeficiency chimeric virus in macaque and human peripheral blood mononuclear cells

We investigated apoptosis induced by in vitro infection with the chimeric virus of simian immunodeficiency virus and human immunodeficiency virus (SHIV). Macaque and human peripheral blood mononuclear cells (PBMCs) were infected with pathogenic SHIV-89.6p (89.6p) or nonpathogenic SHIV-NM-3rN (NM-3rN). In macaque PBMCs, the extent of virus production and apoptosis induction in CD4(+) cells was much greater in 89.6p infection than in NM-3rN infection. The result was consistent with our previous study of in vivo SHIV infection. In human PBMCs, 89.6p replicated and induced apoptosis more extensively than did NM-3rN, when the cells were infected with the same infectious doses of the viruses. However, in cells infected with a high dose of NM-3rN, the levels of virus production and apoptosis induction were comparable to those in 89.6p infection. There was no significant difference in the extent of apoptosis induction between 89.6p and NM-3rN infection when growth curves of the two viruses matched. Thus, apoptosis induction by SHIV might depend quantitatively on the amount of virus production rather than on the strains of the virus. Moreover, the correlation between the extent of apoptosis induction and virus pathogenicity in macaque PBMCs has also been found in SHIV-infected macaques. This suggests that the profiles of SHIV infection in vitro reflect the in vivo phenomena. Therefore, the in vitro evaluation of apoptosis induction by SHIV could be useful as a safety test for the development of live-attenuated vaccines.

Requirement of calmodulin binding by HIV-1 gp160 for enhanced FAS-mediated apoptosis

Accelerated apoptosis is one mechanism proposed for the loss of CD4+ T-lymphocytes in human immunodeficiency virus type 1 (HIV-1) infection. The HIV-1 envelope glycoprotein, gp160, contains two C-terminal calmodulin-binding domains. Expression of gp160 in Jurkat T-cells results in increased sensitivity to FAS- and ceramide-mediated apoptosis. The pro-apoptotic effect of gp160 expression is blocked by two calmodulin antagonists, tamoxifen and trifluoperazine. This enhanced apoptosis in response to FAS antibody or C(2)-ceramide is associated with activation of caspase 3, a critical mediator of apoptosis. A point mutation in the C-terminal calmodulin-binding domain of gp160 (alanine 835 to tryptophan, A835W) eliminates gp160-dependent enhanced FAS-mediated apoptosis in transiently transfected cells, as well as in vitro calmodulin binding to a peptide corresponding to the C-terminal calmodulin-binding domain of gp160. Stable Tet-off Jurkat cell lines were developed that inducibly express wild type gp160 or gp160A835W. Increasing expression of wild type gp160, but not gp160A835W, correlates with increased calmodulin levels, increased apoptosis, and caspase 3 activation in response to anti-FAS treatment. The data indicate that gp160-enhanced apoptosis is dependent upon calmodulin up-regulation, involves the activation of caspase 3, and requires calmodulin binding to the C-terminal binding domain of gp160.

Apoptosis induced by infection of primary brain cultures with diverse human immunodeficiency virus type 1 isolates: evidence for a role of the envelope

Apoptosis of neurons and astrocytes is induced by human immunodeficiency type 1 (HIV-1) infection in vitro and has been demonstrated in brain tissue from patients with AIDS. We analyzed a panel of diverse HIV-1 primary isolates for the ability to replicate and induce neuronal and astrocyte apoptosis in primary human brain cultures. Apoptosis was induced three- to eightfold by infection with the blood-derived HIV-1 isolates 89.6, SG3, and ADA. In contrast, the brain-derived HIV-1 isolates YU2, JRFL, DS-br, RC-br, and KJ-br did not induce significant levels of apoptosis. The ability of HIV-1 isolates to induce apoptosis was independent of their replication capacity. Studies of recombinant chimeras between the SG3 and YU2 viruses showed that replacement of the YU2 Env with the SG3 Env was sufficient to confer the ability to induce apoptosis to the YU2 virus. Replacement of the Env V3 regions alone largely conferred the phenotypes of the parental clones. The SG3 Env used CXCR4 and CCR3 as coreceptors for virus entry, whereas YU2 used CCR5 and CCR3. The V3 regions of SG3 and YU2 conferred the ability to use CXCR4 and CCR5, respectively. In contrast, the 3' region of Env, particularly the C3V4 region, was required in conjunction with the V3 region for efficient use of CCR3. These results provide evidence that Env is a major determinant of neurodegenerative mechanisms associated with HIV-1 infection in vitro and raise the possibility that blood-derived viruses which emerge during the late stages of disease may affect disease progression in the central nervous system.