Human Immunodeficiency Virus Propagation Research Articles

A Multi-Scale Model for the Spread of HIV in a Population Considering the Immune Status of People

A multi-scale mathematical model is proposed, seeking to describe the propagation of Human Immunodeficiency Virus (HIV) in a group of young people between 15 and 24 years of age, through unprotected sexual contact. The uses of antiretroviral therapy (ART) and therapeutic failure are considered to show how the rate of propagation and prevalence are affected. The model consists of a complex network modeling the interactions on the population scale, coupled with the immunological dynamics of each individual, which is modeled by a system of differential equations. The immunological model allows to observe some known facts from the literature, such as to control HIV infection in the immune system, it is necessary to reduce the probability of healthy CD4 T cells becoming infected or increase the probability at which cells of the specific cell response against HIV eliminate infected CD4 T cells. At the population level, it is shown that, to have a high prevalence, it is not necessary for the virus to spread rapidly at the beginning of the simulation time. Additionally, it is observed that a greater number of sexual partners induces higher HIV prevalence. Using ART in the immune system reduces the number of infected CD4 T cells and, consequently, helps to reduce the spread of infection at the population scale. An important result observed in simulations is that the average number of HIV carriers who abandon ART is greater than those who access it. The study adds to the available literature an original simulation model that describes the dynamics of HIV propagation in a population, considering the immune state of people within that population, and serves as a basis for future research involving more detailed aspects aiming for a model closest to reality.

Intracellular immunization against HIV infection with an intracellular antibody that mimics HIV integrase binding to the cellular LEDGF protein

Preventing the protein-protein interaction of the cellular chromatin binding protein Lens Epithelium-Derived Growth Factor (LEDGF) and human immunodeficiency virus (HIV) integrase is an important possible strategy for anti-viral treatment for AIDS. We have used Intracellular Antibody Capture technology to isolate a single VH antibody domain that binds to LEDGF. The crystal structure of the LEDGF-VH complex reveals that the single domain antibody mimics the effect of binding of HIV integrase to LEDGF which is crucial for HIV propagation. CD4-expressing T cell lines were constructed to constitutively express the LEDGF-binding VH and these cells showed interference with HIV viral replication, assayed by virus capsid protein p24 production. Therefore, pre-conditioning cells to express antibody fragments confers effective intracellular immunization for preventing chronic viral replication and can be a way to prevent HIV spread in infected patients. This raises the prospect that intracellular immunization strategies that focus on cellular components of viral integrase protein interactions can be used to combat the problems associated with latent HIV virus re-emergence in patients. New genome editing development, such as using CRISPR/cas9, offer the prospect intracellularly immunized T cells in HIV+ patients.

Autophagy for Better or Worse during Infectious Diseases

Autophagy describes at least three metabolic pathways that deliver cytoplasmic constituents for lysosomal degradation (1). While micro- and chaperone-mediated autophagy engulf or translocate cytosolic material at the late endosomal or lyosomal membrane, respectively, macroautophagy can use different membrane sources, including endoplasmic reticulum, Golgi, plasma membrane, mitochondria, and outer nuclear membrane to enclose large portions of the cytoplasm in autophagosomes (2). These double membrane surrounded vesicles are generated de novo around macroautophagy cargo like damaged organelles, protein aggregates, and cytosolic pathogens, and more than 30 autophagy related (Atg) gene products are involved in their formation and fusion with lysosomes. The series of review articles in this Frontiers in Immunology e-book will high-light how regulation of macroautophagy during infections results in cytosolic restriction of pathogens, sometimes supports their replication and is connected to innate immune activation as well as adaptive immune responses to these environmental insults. In the first set of reviews, the interactions of pathogens with macroautophagy will be discussed. Dengjel and coworkers will summarize the regulation of macroautophagy by influenza A virus and how this changes macroautophagic flux (3). This review particularly focuses on the sequential recruitment of substrates to autophagosomes and interference by influenza A virus. A second review by Biard-Piechaczyk and coauthors will then discuss the different functions that macroautophagy has during human immunodeficiency virus (HIV) infection of T cells and macrophages (4). Differences in the viral replication within these two host cells appear to determine the role that macroautophagy plays in HIV propagation in these targets. Furthermore, Faure and coworkers will high-light that there are certain nodes in the macroautophagy network that are targeted by many viruses (5). Particularly the GTPase IRGM will be discussed. Moreover, Taylor and colleague will discuss the regulation of macroautophagy by herpesviruses (6). Atg6/Beclin-1 targeting by these pathogens has resulted in fascinating insights and tools to dissect macroautophagy. Finally, this block of reviews is concluded with a text by Sasakawa and coworkers (7). They discuss the restriction of bacterial dissemination by macroautophagy and the counter responses of the bacteria aimed at escaping these immune measures. Thus, many pathogens regulate and are restricted by macroautophagy during infection. A second set of reviews explores the role of macroautophagy in immune responses. Innate immune recognition, resulting cytokine production, antigen processing for MHC presentation, and autoimmunity will be discussed in this block. Lee and coworkers will discuss how macroautophagy regulates pathogen detection by the immune system (8). Both the turnover of cytosolic receptors of pathogen associated molecular patterns (PAMPs) and the transport of PAMPs to vesicular receptors is affected by macroautophagy. Moreover, early innate cytokine production is regulated by this pathway. Harris discusses the influence of macroautophagy on IL-1 production (9). Furthermore, Villadangos and colleague highlight the role of macroautophagy in innate and adaptive immunity, covering its role in antigen processing, as well as in T and B cell physiology (10). Expanding on some of these themes, Albert and co-worker summarize the evidence that macroautophagy contributes to exogenous antigen cross-presentation onto MHC class I molecules (11) and focus on the role of the antigen donor cell. In a second review on antigen processing via macroautophagy, the role of this pathway in MHC class II antigen processing will be discussed (12). Particularly, its contribution to both intracellular and extracellular antigen processing will be considered. Beyond antigen processing, He and colleagues will review the role for macroautophagy in lymphocyte development and function (13). This article focuses on the role of macroautophagy in T cells. Finally, Eissa and coauthor summarize how macroautophagy alterations might lead to hyperreactivity to gut commensals and autoimmunity (14). In this respect genetic predisposition to Crohn's disease, which affects essential autophagy genes, will be discussed. Thus, this second set of reviews captures the breadth of functions for macroautophagy in immunity. Macroautophagy is, therefore, not only an essential metabolic pathway, but has also been used during the co-evolutionary struggle between pathogens and their hosts to benefit one or the other. One would predict that it may also play a role in many other infectious diseases, and consequently, could serve as a therapeutic target. However, since macroautophagy can serve the immune system or be exploited by the pathogen, its role has to be characterized for every single different pathogen in order to predict the effect its manipulation would have during infection.

Identification of novel silent HIV propagation routes in Pakistan

Human immunodeficiency virus (HIV) is rapidly increasing in both high risk groups and the general population. In this study, silent routes of propagation in teenaged Pakistanis are discussed. In order to promote sexual activity in youths, regular clients write contact details of sex workers on the doors of public washrooms. HIV prevalence is much higher among Hijra sex workers. Hijra sex workers have apparently stepped into the profession of begging at public places, where they earn money by both begging and distributing visiting cards offering unsafe sex. In many educational institutes, sex education is lacking or absent; if delivered via teachers, government agencies and nongovernmental organizations this could prevent a future epidemic of sexually transmitted infections in Pakistan.

A novel telecommunications-based approach to HIV modeling and simulation

It is well known that biological systems utilize communication in some form; one prolific example of this is the propagation of HIV (Human Immunodeficiency Virus) in the human body. By modeling HIV infection as a communication system, we hope to gain a unique insight into HIV and biological communication systems in general. Such a model would provide researchers a platform for experimenting and simulating various biological communication systems. We have previously developed a layered communication protocol for interpreting biological communication systems using telecommunications paradigms and will apply said model to HIV proliferation. We will also demonstrate the effectiveness of the model by implementing a communication-based simulation of HIV infection based on direct interpretation of this layered protocol.

A model of partial differential equations for HIV propagation in lymph nodes

A system of partial differential equations is used to model the dissemination of the Human Immunodeficiency Virus (HIV) in CD4+T cells within lymph nodes. Besides diffusion terms, the model also includes a time-delay dependence to describe the time lag required by the immunologic system to provide defenses to new virus strains. The resulting dynamics strongly depends on the properties of the invariant sets of the model, consisting of three fixed points related to the time independent and spatial homogeneous tissue configurations in healthy and infected states. A region in the parameter space is considered, for which the time dependence of the space averaged model variables follows the clinical pattern reported for infected patients: a short scale primary infection, followed by a long latency period of almost complete recovery and third phase characterized by damped oscillations around a value with large HIV counting. Depending on the value of the diffusion coefficient, the latency time increases with respect to that one obtained for the space homogeneous version of the model. It is found that same initial conditions lead to quite different spatial patterns, which depend strongly on the latency interval.

New cholesterol-specific antibodies remodel HIV-1 target cells’ surface and inhibit their in vitro virus production

The importance of membrane rafts in HIV-1 infection is still in the focus of interest. Here, we report that new monoclonal anticholesterol IgG antibodies (ACHAs), recognizing clustered membrane cholesterol (e.g., in lipid rafts), rearrange the lateral molecular organization of HIV-1 receptors and coreceptors in the plasma membrane of HIV-1 permissive human T-cells and macrophages. This remodeling is accompanied with a substantial inhibition of their infection and HIV-1 production in vitro. ACHAs promote the association of CXCR4 with both CD4 and lipid rafts, consistent with the decreased lateral mobility of CXCR4, while Fab fragments of ACHAs do not show these effects. ACHAs do not directly mask the extracellular domains of either CD4 or CXCR4 nor do they affect CXCR4 internalization. No significant inhibition of HIV production is seen when the virus is preincubated with the antibodies prior to infection. Thus, we propose that the observed inhibition is mainly due to the membrane remodeling induced by cholesterol-specific antibodies on the target cells. This, in turn, may prevent the proper spatio-temporal juxtaposition of HIV-1 glycoproteins with CD4 and chemokine receptors, thus negatively interfering with virus attachment/entry.

Blind spots in the epidemiology of HIV in black Americans

In the USA, annual rates of new human immunodeficiency virus (HIV)/AIDS diagnoses are seven and 21 times higher in black men and women, respectively, than in whites. Epidemiological inquiry on this disparity has chiefly focused on contextual factors; such emphasis has eclipsed study of direct HIV vectors. The US Centers for Disease Control and Prevention recently announced its intention to curb HIV propagation in black communities, recommending culturally appropriate HIV/AIDS strategies. Contemplated societal interventions should be informed by data evaluating more direct (and under-assessed) HIV transmission vectors, specifically anal intercourse and unsuspected blood exposures. This recommendation involves tracing sexual and non-sexual contacts of recently infected persons and uninfected controls, coupled with DNA sequencing of HIV isolates. Public health authorities do not know the extent to which unmeasured yet plausible HIV transmission vectors can account for ethnic disparities. Appropriate prevention strategies depend critically on direct, rather than ecologic, evidence.

Inefficient Human Immunodeficiency Virus Replication in Mobile Lymphocytes

Cell-to-cell viral transfer facilitates the spread of lymphotropic retroviruses such as human immunodeficiency virus (HIV) and human T-cell leukemia virus (HTLV), likely through the formation of "virological synapses" between donor and target cells. Regarding HIV replication, the importance of cell contacts has been demonstrated, but this phenomenon remains only partly characterized. In order to alter cell-to-cell HIV transmission, we have maintained cultures under continuous gentle shaking and followed viral replication in this experimental system. In lymphoid cell lines, as well as in primary lymphocytes, viral replication was dramatically reduced in shaken cultures. To document this phenomenon, we have developed an assay to assess the relative contributions of free and cell-associated virions in HIV propagation. Acutely infected donor cells were mixed with carboxyfluorescein diacetate succinimidyl ester-labeled lymphocytes as targets, and viral production was followed by measuring HIV Gag expression at different time points by flow cytometry. We report that cellular contacts drastically enhance productive viral transfer compared to what is seen with infection with free virus. Productive cell-to-cell viral transmission required fusogenic viral envelope glycoproteins on donor cells and adequate receptors on targets. Only a few syncytia were observed in this coculture system. Virus release from donor cells was unaffected when cultures were gently shaken, whereas virus transfer to recipient cells was severely impaired. Altogether, these results indicate that cell-to-cell transfer is the predominant mode of HIV spread and help to explain why this virus replicates so efficiently in lymphoid organs.

Alcohol Abuse Enhances Neuroinflammation and Impairs Immune Responses in an Animal Model of Human Immunodeficiency Virus-1 Encephalitis

Neuroinflammatory disorders (including human immunodeficiency virus-1 encephalitis, HIVE) are associated with oxidative stress and inflammatory brain injury, and excessive alcohol use can exacerbate tissue damage. Using a murine model of HIVE, we investigated the effects of alcohol abuse on the clearance of virus-infected macrophages and neuroinflammation. Severe combined immunodeficient mice were reconstituted with human lymphocytes, and encephalitis was induced by intracranial injection of HIV-1-infected monocyte-derived macrophages (HIV-1(+) MDM). Animals were fed an ethanol-containing diet beginning 2 weeks before lymphocyte engraftment and for the entire duration of the experiment. Lymphocyte engraftment was not altered by ethanol exposure. Alcohol-mediated immunosuppression in ethanol-fed mice was manifested by a significant decrease in CD8(+)/interferon-gamma(+) T lymphocytes, a fivefold increase in viremia, and diminished expression of immunoproteasomes in the spleen. Although both groups showed similar amounts of CD8(+) T-lymphocyte infiltration in brain areas containing HIV-1(+) MDMs, ethanol-fed mice featured double the amounts of HIV-1(+) MDMs in the brain compared to controls. Ethanol-exposed mice demonstrated higher microglial reaction and enhanced oxidative stress. Alcohol exposure impaired immune responses (increased viremia, decreased immunoproteasome levels, and prevented efficient elimination of HIV-1(+) MDMs) and enhanced neuroinflammation in HIVE mice. Thus, alcohol abuse could be a co-factor in progression of HIV-1 infection of the brain.

Comment on "Inhibition of Hepatitis B Virus Replication by APOBEC3G"

The cytidine deaminase APOBEC3G (A3G) was recently identified as a natural resistance gene that restricts efficient propagation of human immunodeficiency virus and other retroviruses. The enzyme induces massive cytidine to uridine (C→ U) deamination of single-stranded retroviral DNA, resulting in

PSC-RANTES blocks R5 human immunodeficiency virus infection of Langerhans cells isolated from individuals with a variety of CCR5 diplotypes.

Topical microbicides that effectively block interactions between CCR5(+) immature Langerhans cells (LC) residing within genital epithelia and R5 human immunodeficiency virus (HIV) may decrease sexual transmission of HIV. Here, we investigated the ability of synthetic RANTES analogues (AOP-, NNY-, and PSC-RANTES) to block R5 HIV infection of human immature LC by using a skin explant model. In initial experiments using activated peripheral blood mononuclear cells, each analogue compound demonstrated marked antiviral activity against two R5 HIV isolates. Next, we found that 20-min preincubation of skin explants with each RANTES analogue blocked R5 HIV infection of LC in a dose-dependent manner (1 to 100 nM) and that PSC-RANTES was the most potent of these compounds. Similarly, preincubation of LC with each analogue was able to block LC-mediated infection of cocultured CD4(+) T cells. Competition experiments between primary R5 and X4 HIV isolates showed blocking of R5 HIV by PSC-RANTES and no evidence of increased propagation of X4 HIV, data that are consistent with the specificity of PSC-RANTES for CCR5 and the CCR5(+) CXCR4(-) phenotype of immature LC. Finally, when CCR5 genetic polymorphism data were integrated with results from the in vitro LC infection studies, PSC-RANTES was found to be equally effective in inhibiting R5 HIV in LC isolated from individuals with CCR5 diplotypes known to be associated with low, intermediate, and high cell surface levels of CCR5. In summary, PSC-RANTES is a potent inhibitor of R5 HIV infection in immature LC, suggesting that it may be useful as a topical microbicide to block sexual transmission of HIV.

The effect of substrates on the kinetics and the in vivo threshold activity of mutant HIV-1 proteases.

The role of the human immunodeficiency virus (HIV) protease in the processing of gag and gag-pol polyproteins is essential for the maturation and the life cycle of the virus. The great potential of HIV protease as a therapeutic target for treating the acquired immunodeficiency syndrome, AIDS, has now been confirmed by the recent success of HIV inhibitor drugs to suppress HIV propagation in clinical trials (Ho et al, 1995; Wei et al., 1995; Coffin, 1995). In spite of the success, a serious problem associated with the clinical use of HIV protease inhibitor drugs is the rapid development of drug resistance by HIV. The basis of this drug resistance is the rapid propagation of HIV in the human body and the selection of resistance strains of the virus containing mutant proteases in the presence of inhibitor drugs (Coffin, 1995). The molecular basis of the resistance, therefore, resides on the properties of mutant proteases of the resistant HIV strains, which must have sufficient catalytic activity to support the viral propagation, yet a reduced sensitivity toward the inhibitors. This separate modulation of catalytic and inhibition activities in mutant HIV-1 proteases have now been demonstrated in many laboratories.

Infection of human thymic dendritic cells with HIV-1 induces the release of a cytotoxic factor(s).

Lymphoid organs have been reported to represent the major site for the establishment and the propagation of human immunodeficiency virus (HIV-l) (1). HIV-1 infection is characterized by a permanent high-level of viral replication associated with a high-level turnover of CD4+ T cells (2). The late stages of the disease are characterized by a progressive depletion of CD4+ T cells that eventually lead to the development of the acquired immune deficiency syndrome (AIDS). A variety of direct and indirect mechanisms have been proposed to account for the decline of the CD4+ T cells (3). Among them, inappropriate activation of apoptosis, a programmed cell death process, has been proposed to contribute to the CD4+ T cell depletion (4). HIV-induced apoptotic cell death has been demonstrated not only in vitro but also in infected individuals and is now considered to be a major mechanism of HIV-mediated cell death (5–7).

Epitopes for natural antibodies of human immunodeficiency virus (HIV)-negative (normal) and HIV-positive sera are coincident with two key functional sequences of HIV Tat protein.

We have previously shown that IgM antibodies that react with human immunodeficiency virus (HIV) Tat, a regulatory protein essential for viral replication, are present in sera of all normal, HIV-negative individuals and deficient in sera of HIV-positive individuals at progressively greater frequency as diagnosis of AIDS nears. That IgM was designated as a set of natural antibodies, a repertoire of the normal humoral immune system believed to provide early defense against infectious invaders. In the prior study, by means of a series of synthetic peptides representing the amino acid sequence of HIV-1 Tat, one epitope for the IgM natural antibodies was defined within the cysteine-rich domain, shown in cell transfection studies to participate in Tat function. In this study we have defined another epitope, within the basic domain, with which the natural antibodies react. The specific sequence and amino acid residues required for that epitope are coincident with those required for the role of Tat in viral replication. The IgM antibodies reactive with the two epitopes of Tat make up two distinct sets, which, together, account for the total Tat reactivity of both HIV-negative and HIV-positive sera. The striking coincidence of the two epitopes with the two functional sequences of Tat suggests a potential role of those natural antibodies in control of HIV pathogenesis. By inference from the extensive evidence for the presence of extracellular Tat in cultures of HIV-infected cells, Tat may be expected to be present in the circulating plasma of infected people. We propose, therefore, that the Tat-reactive natural antibodies, documented in these studies to be present in the circulating plasma in the pre-AIDS stages of HIV infection, may inhibit cell entry of plasma-borne Tat and thereby curtail HIV propagation. Thus, those natural antibodies may be a host factor for delay in HIV pathogenetic progression.

Efficient isolation and propagation of human immunodeficiency virus on recombinant colony-stimulating factor 1-treated monocytes.

Monocytes were maintained in tissue culture for greater than 3 mo in media supplemented with rCSF-1. These cultures provided susceptible target cells for isolation and propagation of virus from PBMC of HIV-infected patients. HIV isolated into monocytes readily infected other rCSF-1-treated monocytes but only inefficiently infected PHA-stimulated lymphoblasts. Similarly, laboratory HIV strains passaged in T cell lines or virus isolated from patients' leukocytes into PHA-stimulated lymphoblasts inefficiently infected rCSF-1-treated monocytes. Persistent, low-level virion production was detected in macrophage culture fluids by reverse transcriptase activity or HIV antigen capture through 6-7 wk. Marked changes in cell morphology with cell death, syncytia, and giant cell formation were observed in monocyte cultures 2 wk after infection, but at 4-6 wk, all cells appeared morphologically normal. However, the frequency of infected cells in these cultures at 6 wk was 60-90% as quantified by in situ hybridization with HIV RNA probes or by immunofluorescence with AIDS patients' sera. Ultrastructural analysis by EM also showed a high frequency of infected cells; virtually all HIV budded into and accumulated within cytoplasmic vacuoles and virus particles were only infrequently associated with the plasma membrane. Retention of virus within macrophages and the macrophage tropism of HIV variants may explain mechanisms of both virus persistence and dissemination during disease.

Improved tissue culture technique for production of poorly replicating human immunodeficiency virus strains

We present an improved culture technique for propagation of human immunodeficiency virus (HIV) strains that grow slowly, yield low reverse transcriptase activity and can be transmitted poorly, if at all, to cell lines. By using the Jurkat-tat III cell line 29 (of 30) of these slow/low HIV strains, including one West African strain, could be shown to replicate over a period of several weeks.