The relevance of apoptosis to AIDS pathogenesis

Several recent experimental findings support the hypothesis that apoptosis induced by human immune deficiency virus (HIV) is important in the pathogenesis of acquired immune deficiency syndrome (AIDS). Thus, one potential therapeutic strategy against AIDS may be to block the HIV-mediated apoptosis signal transduction pathway. Induction of apoptosis by HIV infection may prove a useful paradigm for the pathogenesis of a wide range of diseases that involve cell depletion and tissue atrophy.     

Pathogenesis of human immunodeficiency virus infection.

The lentivirus human immunodeficiency virus (HIV) causes AIDS by interacting with a large number of different cells in the body and escaping the host immune response against it. HIV is transmitted primarily through blood and genital fluids and to newborn infants from infected mothers. The steps occurring in infection involve an interaction of HIV not only with the CD4 molecule on cells but also with other cellular receptors recently identified. Virus-cell fusion and HIV entry subsequently take place. Following virus infection, a variety of intracellular mechanisms determine the relative expression of viral regulatory and accessory genes leading to productive or latent infection. With CD4+ lymphocytes, HIV replication can cause syncytium formation and cell death; with other cells, such as macrophages, persistent infection can occur, creating reservoirs for the virus in many cells and tissues. HIV strains are highly heterogeneous, and certain biologic and serologic properties determined by specific genetic sequences can be linked to pathogenic pathways and resistance to the immune response. The host reaction against HIV, through neutralizing antibodies and particularly through strong cellular immune responses, can keep the virus suppressed for many years. Long-term survival appears to involve infection with a relatively low-virulence strain that remains sensitive to the immune response, particularly to control by CD8+ cell antiviral activity. Several therapeutic approaches have been attempted, and others are under investigation. Vaccine development has provided some encouraging results, but the observations indicate the major challenge of preventing infection by HIV. Ongoing research is necessary to find a solution to this devastating worldwide epidemic.     

Rapid evolution of human immunodeficiency virus strains with increased replicative capacity during the seronegative window of primary infection.

The relationship between host and virus was examined during the initial stages of human immunodeficiency virus type 1 (HIV) infection in a volunteer from the Multicenter AIDS Cohort Study (MACS). The individual was asymptomatic and unaware of his infection during an initial donation of blood and inguinal lymphoid tissue. Proviral DNA, however, was present in cells from both sources, HIV RNA was detected in the plasma, and CD4+ cell levels were reduced by approximately 50% compared with previous donations in the MACS. In a second blood donation 12 days later, plasma HIV RNA increased 200-fold in tandem with viral isolates with an increased growth phenotype in vitro. HIV burden was ultimately suppressed upon seroconversion and the emergence of HIV-specific CD8+ cytotoxic T lymphocytes. These observations provide further evidence that the potential benefits of early treatment may be maximized during the early stages of infection, when viral fitness may be low but is unopposed by immune responses.     

Suppression of HIV replication using RNA interference against HIV-1 integrase

RNA interference (RNAi) has become one of the most powerful and popular approach on gene silencing in clinical research study especially in virology due to the gene-specific suppression property of small interfering RNA (siRNA). In this report, we demonstrate that expression of vector-mediated small hairpin RNA (shRNA) against human immunodeficiency virus type 1 (HIV-1) integrase (IN), one of the three important enzymes in HIV infection by controlling the integration of viral RNA to host DNA, could suppress the protein synthesis of EGFP-tagged IN in HeLa cell model efficiently. Furthermore, we show that IN shRNA can successfully reduce the HIV particles production in 293T cells at the level similar to the positive control of HIV-1 tat shRNA. These results provide the therapeutic possibility of HIV replication using RNAi against HIV-1 integrase.     

Short interfering RNA-mediated inhibition of herpes simplex virus type 1 gene expression and function during infection of human keratinocytes

RNA interference (RNAi) is an antiviral mechanism that is activated when double-stranded RNA is cleaved into fragments, called short interfering RNA (siRNA), that prime an inducible gene silencing enzyme complex. We applied RNAi against a herpes simplex virus type 1 (HSV-1) gene, glycoprotein E, which mediates cell-to-cell spread and immune evasion. In an in vitro model of infection, human keratinocytes were transfected with siRNA specific for glycoprotein E and then infected with wild-type HSV-1. RNAi-mediated gene silencing reproduced the small plaque phenotype of a gE-deletion mutant virus. The specificity of gene targeting was demonstrated by flow cytometry and Northern blot analyses. Exogenous siRNA can suppress HSV-1 glycoprotein E expression and function during active infection in vitro through RNAi. This work establishes RNAi as a genetic tool for the study of HSV and provides a foundation for development of RNAi as a novel antiviral therapy.     

Are general practitioners ready to prevent the spread of HIV?

General practitioners are excellently placed to assess a person''s risk of being infected with the human immunodeficiency virus (HIV) and to give advice on reducing that risk. Their attitudes to the acquired immune deficiency syndrome (AIDS) and infection with HIV are, however, unknown. A questionnaire survey of 196 general practitioners in East Berkshire Health District was used to assess general practitioners'' readiness to undertake opportunistic health education to prevent the spread of infection with HIV. Altogether 132 replied. Sixty four of them expressed little interest in health education about HIV, and one in six would not dissent from the notion that AIDS could be controlled only by criminalising homosexuality. Only 75 of them had initiated discussions about HIV with patients. Moreover, many underestimated the risks from heterosexual sex while exaggerating the risks from non-sexual contact.Advice from general practitioners if given extensively might reduce the spread of infection with HIV. How best this may be achieved needs to be considered urgently.     

The Progress on the Studies of HIV/AIDS Vaccine

人类控制HIV感染长远的目标是发展安全、有效、廉价的HIV AIDS疫苗。但经 2 0多年的努力 ,人类探索HIV AIDS疫苗之路仍在继续。分析了疫苗研究的复杂性和发展HIV AIDS疫苗过程中所面临的挑战 ,并对发展HIV AIDS疫苗的可能性从实验和临床方面进行了阐述。同时结合HIV感染的免疫应答原理对现有的各种HIV AIDS疫苗研究策略作一综述 ,并根据以往HIV AIDS疫苗研究的经验和教训提出未来疫苗的发展思路及展望。     

Structure and design of broadly-neutralizing antibodies against HIV

Since the discovery more than 30 years ago of human immunodeficiency virus (HIV) as the causative agent of the deadly disease, acquired immune deficiency disease (AIDS), there have been no efficient vaccines against the virus. For the infection of the virus, the HIV surface glycoprotein gp120 first recognizes the CD4 receptor on the target helper T-cell, which initiates HIV fusion with the target cell and, if unchecked, leads to destruction of the patient's immune system. Despite the difficulty of developing appropriate immune responses in HIV-infected individuals, patient sera often contain antibodies that have broad neutralization activity, indicating the possibility of immunological treatment and prevention. Recently, through extensive structural studies of neutralizing antibodies of HIV in complex with gp120, the critical mechanisms of broad neutralization against HIV have been elucidated. Based on these discoveries, the structure-aided designs of antibodies and novel scaffolds were performed to create extremely potent neutralizing antibodies against HIV. These new discoveries and advances shed light on the road to development of efficient immunological therapies against AIDS.     

The use of ribozyme gene therapy for the inhibition of HIV replication and its pathogenic sequelae

Human immunodeficiency virus (HIV) is a lentivirus, a separate genus of the Retroviridae which are RNA viruses that integrate as DNA copies into the genomes of host cells and replicate intracellularly through various RNA intermediates. Several of these RNA molecules can be targeted by ribozymes and a number of investigators, including our group, have demonstrated the ability of ribozymes to suppress HIV replication in cultured cells. It is argued that the use of this ribozyme gene therapy approach for the treatment of HIV infection may act as an adjunct to chemotherapeutic drugs and may affect not just viral suppression, but also immune restoration. This approach can be tested in Clinical Trials, several of which are currently under way.     

A mathematical model of vaccination against HIV to prevent the development of AIDS.

Vaccination and post-exposure immunization against the human immunodeficiency viruses (HIV-1 and HIV-2) faces the problem of the extensive genetic and antigenic variability of these viruses. This raises the question of what fraction of all possible antigen strains of the virus must be recognized by the immune response to a vaccine to prevent development of acquired immunodeficiency disease (AIDS). The success of a vaccine can depend on the variability of the target epitopes. The different HIV variants must be suppressed faster than new escape mutants can be produced. In this paper the antigenic variation of HIV during an individual infection is described by a stochastic process. The central assumption is that antigenic drift is important for the virus to survive immunological attack and to establish a persistent infection that leads to the development of AIDS after a long incubation period. The mathematical analysis reveals that the fraction of antigenic variants recognized by the immune response, that is induced by a successful immunogen, must exceed 1-1/R, where R is the diversification rate of the virus population. This means that if each HIV strain can produce, on average, five new escape mutants, then more than 80% of the possible variants must be covered by the immunogen. A generic result of the model is that, no matter how immunogenic a vaccine is, it will fail if it does not enhance immune attack against a sufficiently large fraction of strains. Furthermore, it is shown that the timing of the application of post-exposure immunization is important.     

Small interfering RNAs against the TAR RNA binding protein, TRBP, a Dicer cofactor, inhibit human immunodeficiency virus type 1 long terminal repeat expression and viral production

RNA interference (RNAi) is now widely used for gene silencing in mammalian cells. The mechanism uses the RNA-induced silencing complex, in which Dicer, Ago2, and the human immunodeficiency virus type 1 (HIV-1) TAR RNA binding protein (TRBP) are the main components. TRBP is a protein that increases HIV-1 expression and replication by inhibition of the interferon-induced protein kinase PKR and by increasing translation of viral mRNA. After HIV infection, TRBP could restrict the viral RNA through its activity in RNAi or could contribute more to the enhancement of viral replication. To determine which function will be predominant in the virological context, we analyzed whether the inhibition of its expression could enhance or decrease HIV replication. We have generated small interfering RNAs (siRNAs) against TRBP and found that they decrease HIV-1 long terminal repeat (LTR) basal expression 2-fold, and the LTR Tat transactivated level up to 10-fold. In the context of HIV replication, siRNAs against TRBP decrease the expression of viral genes and inhibit viral production up to fivefold. The moderate increase in PKR expression and activation indicates that it contributes partially to viral gene inhibition. The moderate decrease in micro-RNA (miRNA) biogenesis by TRBP siRNAs suggests that in the context of HIV replication, TRBP functions other than RNAi are predominant. In addition, siRNAs against Dicer decrease viral production twofold and impede miRNA biogenesis. These results suggest that, in the context of HIV replication, TRBP contributes mainly to the enhancement of virus production and that Dicer does not mediate HIV restriction by RNAi.     

Human immunodeficiency virus infection of monoblastoid cells: cellular differentiation determines the pattern of virus replication.

Stringent control of human immunodeficiency virus (HIV) replication was observed in the human monoblastoid cell line U937. A low-multiplicity infection of these cells by the LAV1 strain of HIV was productive for 2.5 days; then virus replication became restricted and no further evidence of virion production was observed. The dramatic decrease in HIV production was due in part of reduced accumulation of cytoplasmic viral RNA and occurred in the absence of evident cytopathic effects. In contrast, infected cells induced to differentiate by phorbol ester, vitamin D3, or lymphokine supernatant did not release markers of HIV despite the accumulation of significant levels of cytoplasmic viral RNA. HIV infection altered the pattern of c-myc RNA accumulation in U937 cells. Expression of this gene changes normally in response to the state of cellular differentiation; in infected cells the level of c-myc expression was correlated to the levels of viral RNA accumulation and not to cellular differentiation. These results suggest that restricted replication of HIV in monocytes might be an important mechanism of virus persistence and demonstrate a relationship between HIV replication and monocyte differentiation.     

The breakdown of the cytokine network subsequent to human immunodeficiency virus infection

The acquired immunodeflciency syndrome (AIDS) is a clinically multifaceted disease induced by infection with the human immunodeficiency virus (HIV). HIV infection results in a complex pattern of immunologic alterations that leads to the development of AIDS in the majority of HIV seropositive (HIV+) individuals. The reduction in CD4 T lymphocyte counts is the hallmark of HIV infection; nevertheless, long before the reduction in CD4 counts reaches critical levels, a series of profound and complex defects that impair the function of CD4 T lymphocytes can be detected. Thus, HIV infection is characterized by quantitative and qualitative defects affecting CD4 T lymphocytes. It was suggested recently that programmed cell death (PCD) is an important mechanism leading to CD4 depletion in HIV infection, and that susceptibility of peripheral lymphocytes to PCD is differentially regulated by diverse cytokines. Thus, type 1 cytokines would protect CD4 lymphocytes against PCD, whereas type 2 cytokines would not protect against, and could augment, PCD. We suggest that the qualitative alterations of the immune response provoke the CD4 depletion characteristic of HIV disease via type 2 cytokinemediated augmentation of PCD, and are therefore ultimately responsible for the progression of HIV infection. Finally, we summarize recent data showing that three correlates of disease progression: emergence of HIV strains with syncitium-inducing ability (SI), type 1-to-type 2 cytokine shift, and CD4 depletion, are significantly associated, suggesting a complex interconnected virologic-immunologic pathogenesis of HIV infection.     

HIV persistence in monocytes leads to pathogenesis and AIDS

An hypothesis of the pathogenic mechanism leading to acquired immunodeficiency syndrome (AIDS) that places special emphasis on the potential for infected monocytes to act as the reservoir of a persistent human immunodeficiency virus (HIV) infection has been developed. Monocytes may mediate directly the infection and ultimate destruction of helper T cells; this establishes a direct relationship between antigen presentation and HIV dissemination, thus accounting for the cytopathogenic effects and immune system debilitation associated commonly with AIDS. The possibility that this mode of virus dissemination can account for the depletion of helper-T-cell subsets based on their antigen specificity is considered and may explain why the cellular immune response to the virus is ineffective. This concept and may also elucidate the role of intercurrent infections in the development of disease and it suggests mechanistic explanations for the conversion from prodromal to fulminant AIDS.     

Adenosine signaling and adenosine deaminase regulation of immune responses: impact on the immunopathogenesis of HIV infection

Infection by human immunodeficiency virus (HIV) causes the acquired immune deficiency syndrome (AIDS), which has devastating effects on the host immune system. HIV entry into host cells and subsequent viral replication induce a proinflammatory response, hyperactivating immune cells and leading them to death, disfunction, and exhaustion. Adenosine is an immunomodulatory molecule that suppresses immune cell function to protect tissue integrity. The anti-inflammatory properties of adenosine modulate the chronic inflammation and immune activation caused by HIV. Lack of adenosine contributes to pathogenic events in HIV infection. However, immunosuppression by adenosine has its shortcomings, such as impairing the immune response, hindering the elimination of the virus and control of viral replication. By attempting to control inflammation, adenosine feeds a pathogenic cycle affecting immune cells. Deamination of adenosine by ADA (adenosine deaminase) counteracts the negative effects of adenosine in immune cells, boosting the immune response. This review comprises the connection between adenosinergic system and HIV immunopathogenesis, exploring defects in immune cell function and the role of ADA in protecting these cells against damage.     

The Aedes aegypti toll pathway controls dengue virus infection

Aedes aegypti, the mosquito vector of dengue viruses, utilizes its innate immune system to ward off a variety of pathogens, some of which can cause disease in humans. To date, the features of insects' innate immune defenses against viruses have mainly been studied in the fruit fly Drosophila melanogaster, which appears to utilize different immune pathways against different types of viruses, in addition to an RNA interference-based defense system. We have used the recently released whole-genome sequence of the Ae. aegypti mosquito, in combination with high-throughput gene expression and RNA interference (RNAi)-based reverse genetic analyses, to characterize its response to dengue virus infection in different body compartments. We have further addressed the impact of the mosquito's endogenous microbial flora on virus infection. Our findings indicate a significant role for the Toll pathway in regulating resistance to dengue virus, as indicated by an infection-responsive regulation and functional assessment of several Toll pathway-associated genes. We have also shown that the mosquito's natural microbiota play a role in modulating the dengue virus infection, possibly through basal-level stimulation of the Toll immune pathway.     

Microdevices for examining immunological responses of single cells to HIV

More than 60 million people in the world have been diagnosed with HIV infections since the virus was recognized as the causative agent of AIDS in the 1980s. Even though more than half of the infected patients have died, effective disease treatment and prevention measures have not been established. ART (antiretroviral therapy) is the only proven HIV treatment that sustains the suppression of patient viraemia. Current routine approaches to treat HIV infections are targeted at developing vaccines that will induce humoral or cell memory immune responses. However, developing an effective vaccine has been challenging because the HIV mutates rapidly, which allows the virus to evade immune surveillances established against the previous strain. In addition, the virus is able to quickly establish a reservoir and treatment is difficult because of the general lack of knowledge about HIV immune response mechanisms. This review introduces common disease symptoms and the progression of HIV infection with a brief summary of the current treatment approaches. Different cellular immune responses against HIV are also discussed, with emphasis on a nanotechnology research that has focused on probing T-cell response to HIV infection. Furthermore, we discuss recent noteworthy nanotechnology updates on T-cell response screening that is focused on HIV infection. Finally, we review potential future treatment strategies based on the correlations between T-cell response and HIV infection.     

Towards an AIDS vaccine: the role of nonhuman primates

Over the last 10 years, about 20 human immunodeficiency virus (HIV) vaccine candidates have been tried in humans, with disappointing results as gauged by limited immune responses or protection against infection. These difficulties suggest that a new strategy is needed to test systematically new vaccine candidates. That opportunity is now afforded by nonhuman primate models with SIV, which have been shown to provide an excellent mirror of HIV infection in humans. The recent introduction of SHIVs, chimeric viruses that carry the HIV envelope and are able to infect and cause AIDS in monkeys, also has added an important additional research tool. These models can be used to address a series of questions, including the following: (1) Can protection be provided by partial immunity or is sterilizing immunity required? (2) What are the immune parameters that best predict protection against a potentially pathogenic challenge? (3) What role does mucosal immunity play and can it be induced by practical modes of immunization? (4) Can an attenuated virus be selected that is both protective and safe? An orderly strategy for the evaluation of vaccine candidates could be adopted that would involve several phases: (a) the selection of a limited set of challenge models, ranging from very severe to mild and requiring consideration of primate species, age, route of infection, and challenge viruses; (b) the assessment of candidate vaccines using comparable virus challenges; and (c) accelerated testing in humans of any candidate vaccines that have met a 'proof of efficacy' in primates.