Epidermal Langerhans cells--a target for HTLV-III/LAV infection

Mucocutaneous Manifestations of People Living with HIV in Current Antiretroviral Therapy Era

OBJECTIVE

It has been reported that approximately 90% of patients who are infected with human immunodeficiency virus (HIV) have various cutaneous symptoms that are related to the virus. This study aims to describe the cutaneous disorders that have developed in HIV-infected patients and to investigate the factors that may be related, such as relationships to drug use and CD4 counts.

METHODS

This cross-sectional study included people who were living with HIV and being followed by our hospital's infectious diseases clinic after they had been referred to the dermatology clinic because of skin lesions. These patients had been diagnosed with HIV by enzyme-linked immunosorbent assay tests and were included in the study if they were older than 18 years and had agreed to participate. Findings from detailed dermatological examinations were recorded, along with the patients' CD4 counts, the durations of their illnesses, and the treatments they received.

RESULTS

144 patients were included in the study. The most common mucocutaneous manifestation was seborrheic dermatitis, at 28.5% (n = 41). The mean CD4 count was 607.1 (min-max = 10.6-1982).The CD4 counts were divided into three groups in the study as follows: 22 (15.3%) patients with <200, 35 (24.3%) patients between 200 and 500, and 87 (60.4%) patients with >500. There were no statistical differences between these groups in terms of dermatological findings. Nevertheless, the highest rate of patients with three or more dermatological conditions was found among those with CD4 counts <200 (n = 11.50%).

CONCLUSION

Skin manifestations are common in patients who are HIV-positive; however, many skin disorders can be seen in HIV/acquired immunodeficiency syndrome (AIDS) patients whatever CD4 cell counts of these patients are.

Human Dendritic Cell Subsets, Ontogeny, and Impact on HIV Infection

Dendritic cells (DCs) play important roles in orchestrating host immunity against invading pathogens, representing one of the first responders to infection by mucosal invaders. From their discovery by Ralph Steinman in the 1970s followed shortly after with descriptions of their in vivo diversity and distribution by Derek Hart, we are still continuing to progressively elucidate the spectrum of DCs present in various anatomical compartments. With the power of high-dimensional approaches such as single-cell sequencing and multiparameter cytometry, recent studies have shed new light on the identities and functions of DC subtypes. Notable examples include the reclassification of plasmacytoid DCs as purely interferon-producing cells and re-evaluation of intestinal conventional DCs and macrophages as derived from monocyte precursors. Collectively, these observations have changed how we view these cells not only in steady-state immunity but also during disease and infection. In this review, we will discuss the current landscape of DCs and their ontogeny, and how this influences our understanding of their roles during HIV infection.

HIV-1 Trans Infection of CD4(+) T Cells by Professional Antigen Presenting Cells

Since the 1990s we have known of the fascinating ability of a complex set of professional antigen presenting cells (APCs; dendritic cells, monocytes/macrophages, and B lymphocytes) to mediate HIV-1 trans infection of CD4(+) T cells. This results in a burst of virus replication in the T cells that is much greater than that resulting from direct, cis infection of either APC or T cells, or trans infection between T cells. Such APC-to-T cell trans infection first involves a complex set of virus subtype, attachment, entry, and replication patterns that have many similarities among APC, as well as distinct differences related to virus receptors, intracellular trafficking, and productive and nonproductive replication pathways. The end result is that HIV-1 can sequester within the APC for several days and be transmitted via membrane extensions intracellularly and extracellularly to T cells across the virologic synapse. Virus replication requires activated T cells that can develop concurrently with the events of virus transmission. Further research is essential to fill the many gaps in our understanding of these trans infection processes and their role in natural HIV-1 infection.

Toxic epidermal necrolysis and Stevens-Johnson syndrome in South Africa: a 3-year prospective study

BACKGROUND

Toxic Epidermal Necrolysis (TEN) and Stevens-Johnson syndrome (SJS) remain feared medication-related reactions. HIV infection and tuberculosis predispose to drug eruptions, yet there is a paucity of data on TEN/SJS in populations with high prevalences of both diseases.

AIM

The aim of this prospective observational study was to describe the features and outcomes of patients admitted with TEN/SJS at a large academic hospital in South Africa. We aimed to identify poor prognostic indicators and to validate the use of the TEN-specific severity-of-illness score (SCORTEN) in this population.

METHODS

All patients admitted with TEN/SJS over a 3-year period were enrolled. Disease severity was graded according to percentage skin involved and SCORTEN. Co-morbid diagnoses, clinical features, investigations, complications and outcomes were noted.

RESULTS

75 patients (39.9 ± 10.6 years, 16 males, 59 HIV positive) were classified as TEN (n  = 42), TEN/SJS overlap (n = 11) and SJS (n = 22). Twenty-four percent died, most from refractory septic shock. Non-survivors had a higher mean SCORTEN on Days 1 and 3 (1.89 vs. 1.04, P = 0.006 and 2.27 vs. 0.90, P < 0.001). A SCORTEN ≥2 on Days 1 and 3 predicted non-survival (OR = 2.94, P = 0.047; OR = 7.45, P < 0.001). Other predictors of non-survival included HIV infection (OR = 6.01, P = 0.058), HIV-tuberculosis co-infection (OR = 8.5, P < 0.001), ≥40% skin involvement (OR = 20.27, P < 0.001), anaemia (OR = 4.68, P = 0.005), hypoalbuminemia (OR = 8.5, P = 0.001) and severe sepsis (OR = 71.09, P < 0.001).

CONCLUSION

Most patients with TEN/SJS were HIV positive and female. We validated the use of SCORTEN and identified several prognostic indicators, most significant being HIV-tuberculosis co-infection, ≥40% skin involvement and severe sepsis.

Morphological and immunological changes in the skin of autopsied women with AIDS

Acquired immunodeficiency syndrome (AIDS) is characterized by decreased immunity, making a patient more susceptible to opportunistic infections which can have cutaneous manifestations. The aim of this study was to evaluate the local immunity of the skin through morphological and immunohistochemical analysis. Skin samples of 52 women, 27 without AIDS and 25 with AIDS, autopsied in an academic referral hospital in Brazil were evaluated. The autopsy reports and medical records were reviewed, and histochemical Hematoxylin-eosin, Picrosirius red, and Verhoeff stains as well as morphometric (Image J and KS-300 Kontron-Zeiss) and immunohistochemical (S-100 and anti-IgA) analyses of the skin were performed. Women with AIDS presented a thinner epidermis than women without AIDS (33.33 [12.00-317.66] vs 67.42 [12.00-530.02] μm; p < 0.001), with a lower number of epithelial cell layers (4.00 [2.00-11.00] vs 4.00 [2.00-16.00]; p < 0.001), a smaller cell diameter (12.92 [6.00-28.87] vs 24.32 [6.00-33.12] μm; p < 0.001), and a lower number of Langerhans cells (LC) (12.58 [0.00-81.74] vs 31.44 [0.00-169.77] LC/mm(2); p < 0.001). The dermis contained more collagen fibers (8.20 % [2.40-19.40] vs 6.30 % [0.40-13.90]; p < 0.001). Some of these parameters were negatively correlated with viral load and positively correlated with the number of CD4+ T-lymphocytes. We conclude that a decrease of the local skin immunity in women with AIDS may contribute to the development of skin lesions.

HIV impairment of immune responses in dendritic cells

Dendritic cells and their subsets are diverse populations of immune cells in the skin and mucous membranes that possess the ability to sense the presence of microbes and orchestrate an efficient and adapted immune response. Dendritic cells (DC) have the unique ability to act as a bridge between the innate and adaptive immune responses. These cells are composed of a number of subsets behaving with preferential and specific features depending on their location and surrounding environment. Langerhans cells (LC) or dermal DC (dDC) are readily present in mucosal areas. Other DC subsets such as plasmacytoid DC (pDC), myeloid DC (myDC), or monocyte-derived DC (MDDC) are thought to be recruited or differentiated in sites of pathogenic challenge. Upon HIV infection, DC and their subsets are likely among the very first immune cells to encounter incoming pathogens and initiate innate and adaptive immune responses. However, as evidenced during HIV infection, some pathogens have evolved subtle strategies to hijack key cellular machineries essential to generate efficient antiviral responses and subvert immune responses for spread and survival.In this chapter, we review recent research aimed at investigating the involvement of DC subtypes in HIV transmission at mucosal sites, concentrating on HIV impact on cellular signalling and trafficking pathways in DC leading to DC-mediated immune response alterations and viral immune evasion. We also address some aspects of DC functions during the chronic immune pathogenesis and conclude with an overview of the current and novel therapeutic and prophylactic strategies aimed at improving DC-mediated immune responses, thus to potentially tackle the early events of mucosal HIV infection and spread.

The influence of gender and of AIDS on the immunity of autopsied patients' esophagus

Previous studies have shown that males who have AIDS are more frequently affected by infectious diseases than females. The esophagus is the organ in the digestive tube that is more commonly affected by opportunistic infections during the syndrome. The aim of this study was to assess the influence of AIDS and of gender on local immunity of the esophageal epithelium. Fragments of the esophagus from 29 autopsied women and 37 autopsied men were collected at a university hospital from 1980 to 2009 and were divided in groups with and without AIDS. The IgA-, IgG-, and IgM-positive cells and Langerhans cells (LCs) were immunostained, respectively, with anti-IgA, anti-IgG, anti-IgM, and anti-S100. The software Image J was used to measure the esophageal epithelium and to count the epithelium cellular layers. Patients with AIDS, apart from gender, showed an increase in IgA-, IgG-, and IgM-positive cells and a reduction of Langerhans cells, in thickness and in number of cellular layers in the esophageal epithelium. However, among individuals with AIDS, men presented lower secretory expression of IgA-, IgG-, and IgM-positive cells than women and more intense reduction of LCs. Women have naturally presented better local esophageal immunity than men. Although AIDS possibly causes immunological and morphological alterations in the esophageal epithelium in both genders, women have better esophageal immunity, which may explain a greater frequency of hospital admissions due to infection of men with AIDS when compared with women.

New insights into HIV-1-primary skin disorders

Since the first reports of AIDS, skin involvement has become a burdensome stigma for seropositive patients and a challenging task for dermatologist and infectious disease specialists due to the severe and recalcitrant nature of the conditions. Dermatologic manifestations in AIDS patients act as markers of disease progression, a fact that enhances the importance of understanding their pathogenesis.

Broadly, cutaneous disorders associated with HIV type-1 infection can be classified as primary and secondary. While the pathogenesis of secondary complications, such as opportunistic infections and skin tumours, is directly correlated with a decline in the CD4⁺ T cell count, the origin of the certain manifestations primarily associated with the retroviral infection itself still remains under investigation.

The focus of this review is to highlight the immunological phenomena that occur in the skin of HIV-1-seropositive patients, which ultimately lead to skin disorders, such as seborrhoeic dermatitis, atopic dermatitis, psoriasis and eosinophilic folliculitis. Furthermore, we compile the latest data on how shifts in the cytokines milieu, impairments of the innate immune compartment, reactions to xenobiotics and autoimmunity are causative agents in HIV-1-driven skin diseases. Additionally, we provide a thorough analysis of the small animal models currently used to study HIV-1-associated skin complications, centering on transgenic rodent models, which unfortunately, have not been able to fully unveil the role of HIV-1 genes in the pathogenesis of their primarily associated dermatological manifestations.

Host defense mechanisms in secondary syphilitic lesions: a role for IFN-gamma-/IL-17-producing CD8+ T cells?

Cell-mediated immunity is thought to be of critical importance in antisyphilitic host defense, but the exact mechanisms are still unknown. This fact is particularly true for HIV-infected persons with a deficit in CD4+ T-cell number. We therefore obtained lesional skin samples from HIV+ and HIV- patients with secondary syphilis at different time points of lesional age to search both for causative microorganisms and to characterize the inflammatory infiltrate. By doing so, we detected Treponema pallidum spirochetes with a much greater abundance in late lesions of HIV+ individuals compared with the HIV- cohort. The dominating inflammatory cells were T cells, macrophages, and neutrophils at all stages and plasma cells in older lesions. In HIV- persons, T cells consisted of equal numbers of CD4+ and CD8+ T-cells, whereas in HIV+ patients, the majority of T cells belonged to the CD8 lineage and produced both IFN-γ and IL-17. Regulatory T cells and Langerhans cells were reduced in these patients compared with their HIV- counterparts. Because of our observations, we propose that T cells of both the CD4 and CD8 lineage are needed for an at least partial protective antisyphilitic immunity. Compensation mechanisms in HIV+ individuals, such as an increase of Tc1/17 cells as well as a reduction in immunoregulatory Langerhans cells and T cells, apparently do not overcome the deficiencies in these patients to eliminate the spirochete.

Variation in the biological properties of HIV-1 R5 envelopes: implications of envelope structure, transmission and pathogenesis

HIV-1 R5 viruses predominantly use CCR5 as a coreceptor to infect CD4(+) T cells and macrophages. While R5 viruses generally infect CD4(+) T cells, research over the past few years has demonstrated that they vary extensively in their capacity to infect macrophages. Thus, R5 variants that are highly macrophage tropic have been detected in late disease and are prominent in brain tissue of subjects with neurological complications. Other R5 variants that are less sensitive to CCR5 antagonists and use CCR5 differently have also been identified in late disease. These latter variants have faster replication kinetics and may contribute to CD4 T-cell depletion. In addition, R5 viruses are highly variable in many other properties, including sensitivity to neutralizing antibodies and inhibitors that block HIV-1 entry into cells. Here, we review what is currently known about how HIV-1 R5 viruses vary in cell tropism and other properties, and discuss the implications of this variation on transmission, pathogenesis, therapy and vaccines.

HIV reservoirs in vivo and new strategies for possible eradication of HIV from the reservoir sites

Even though the treatment of human immunodeficiency virus (HIV)-infected individuals with highly active antiretroviral therapy (HAART) provides a complete control of plasma viremia to below detectable levels (<40 copies/mL plasma), there is an unequal distribution of all antiretroviral drugs across diverse cellular and anatomic compartments in vivo. The main consequence of this is the acquisition of resistance by HIV to all known classes of currently prescribed antiretroviral drugs and the establishment of HIV reservoirs in vivo. HIV has a distinct advantage of surviving in the host via both pre-and postintegration latency. The postintegration latency is caused by inert and metabolically inactive provirus, which cannot be accessed either by the immune system or the therapeutics. This integrated provirus provides HIV with a safe haven in the host where it is incessantly challenged by its immune selection pressure and also by HAART. Thus, the provirus is one of the strategies for viral concealment in the host and the provirus can be rekindled, through unknown stimuli, to create progeny for productive infection of the host. Thus, the reservoir establishment remains the biggest impediment to HIV eradication from the host. This review provides an overview of HIV reservoir sites and discusses both the virtues and problems associated with therapies/strategies targeting these reservoir sites in vivo.

Esophageal epithelium of women with AIDS: thickness and local immunity

The aim of this study was to evaluate the morphological characteristics of the esophageal epithelium (EE) and its local immunity. Esophageal fragments of autopsied women were collected from 1980 to 2008, and two groups were analyzed: with AIDS (n=17) and without AIDS (n=12). The measurement of the esophageal epithelium was carried out through the image analysis software ImageJ, and the immunostaining of Langerhans cells (LCs) was carried out using anti-S100 antibody. Women with AIDS, when compared with women without AIDS, had significantly thinner EE (220.6 versus 243.5 microm), a less number of LCs (6.2 versus 18.8 LCs/mm(2)), and a higher percentage of immature or morphologically altered LCs (66.6 versus 40.0%). The malnourished women, when compared with normonourished women, regardless of AIDS, had significantly thinner EE (227.1 versus 238.0 microm) and a less number of LCs (6.2 versus 12.5 LCs/mm(2)). The percentage of immature or morphologically altered LCs was the same in both groups. Additionally, the women with AIDS (7.0 versus 2.8%) and the malnourished women (5.8 versus 3.1%) presented a significantly higher percentage of fibrosis. We concluded that AIDS and malnutrition contribute to the decrease in esophagus local immunity and, therefore, to a possible increase in local opportunistic infections.

Vaccines and microbicides preventing HIV-1, HSV-2, and HPV mucosal transmission

HIV-1, herpes simplex virus type 2 (HSV-2), and human papillomavirus (HPV), among other sexually transmitted infections, represent a major burden for global health. Initial insights into the mucosal transmission of these viral pathogens have raised optimism with regard to the rapid generation of protective vaccines. Nevertheless, setbacks for HIV-1 and HSV-2 vaccines have seriously challenged the initial enthusiasm. Recently, two new vaccines that efficiently prevented HPV infection have renewed the hope that vaccinal prevention of viral mucosal sexually transmitted infections is possible. HIV-1 and HSV-2 differ from HPV, and each virus needs to be tackled with a distinct approach. However, vaccines are not the only possible answer. Topically applied agents (microbicides) are an attractive alternative in the prevention of HIV-1 and HSV-2 mucosal transmission. Progress in understanding the mechanisms of genital transmission of HIV-1 and HSV-2 is required for successful vaccine or microbicide candidates to emerge from current approaches.

Primary human immunodeficiency virus type 1-specific CD8+ T-cell responses induced by myeloid dendritic cells

Induction of an antigenically broad and vigorous primary T-cell immune response by myeloid dendritic cells (DC) in blood and tissues could be important for an effective prophylactic or therapeutic vaccine to human immunodeficiency virus type 1 (HIV-1). Here we show that a primary CD8(+) T-cell response can be induced by HIV-1 peptide-loaded DC derived from blood monocytes of HIV-1-negative adults and neonates (moDC) and by Langerhans cells (LC) and interstitial, dermal-intestinal DC (idDC) derived from CD34(+) stem cells of neonatal cord blood. Optimal priming of single-cell gamma interferon (IFN-gamma) production by CD8(+) T cells required CD4(+) T cells and was broadly directed to multiple regions of Gag, Env, and Nef that corresponded to known and predicted major histocompatibility complex class I epitopes. Polyfunctional CD8(+) T-cell responses, defined as single-cell production of more than one cytokine (IFN-gamma, interleukin 2, or tumor necrosis factor alpha), chemokine (macrophage inhibitory factor 1beta), or cytotoxic degranulation marker CD107a, were primed by moDC, LC, and idDC to HIV-1 Gag and reverse transcriptase epitopes, as well as to Epstein-Barr virus and influenza A virus epitopes. Thus, three major types of blood and tissue myeloid DC targeted by HIV-1, i.e., moDC, LC, and idDC, can prime multispecific, polyfunctional CD8(+) T-cell responses to HIV-1 and other viral antigens.

HIV infection of the genital mucosa in women

The vast majority of new HIV infections are acquired via the genital and rectal mucosa. Here, we provide an overview of our current knowledge of how HIV establishes local infection, with an emphasis on viral invasion through the female genital tract. Studies using human explant tissues and in vivo animal studies have improved our understanding of the cellular and molecular pathways of infection; this information could be harnessed to design effective HIV vaccines and microbicides.

Pharmacokinetic-pharmacodynamic relationship of NRTIs and its connection to viral escape: an example based on zidovudine

In HIV disease, the mechanisms of drug resistance are only poorly understood. Incomplete suppression of HIV by antiretroviral agents is suspected to be a main reason. The objective of this in silico study is to elucidate the pharmacokinetic origins of incomplete viral suppression, exemplified for zidovudine (AZT) as a representative of the key class of nucleoside reverse transcriptase inhibitors (NRTIs). AZT, like other NRTIs, exerts its main action through its intra-cellular triphoshate (AZT-TP) by competition with natural thymidine triphosphate. We developed a physiologically based pharmacokinetic (PBPK) model describing the intra-cellular pharmacokinetics of AZT anabolites and subsequently established the pharmacokinetic-pharmacodynamic relationship. The PBPK model has been validated against clinical data of different dosing schemes. We reduced the PBPK model to derive a simple three-compartment model for AZT and AZT-TP that can readily be used in population analysis of clinical trials. A novel machanistic, and for NRTIs generic effect model has been developed that incorporates the primary effect of AZT-TP and potential secondary effect of zidovudine monophosphate. The proposed models were used to analyze the efficacy and potential toxicity of different dosing schemes for AZT. Based on the mechanism of action of NRTIs, we found that drug heterogeneities due to temporal fluctuations can create a major window of unsuppressed viral replication. For AZT, this window was most pronounced for a 600 mg/once daily dosing scheme, in which insufficient viral suppression was observed for almost half the dosing period.

Setting the stage: host invasion by HIV

For more than two decades, HIV has infected millions of people worldwide each year through mucosal transmission. Our knowledge of how HIV secures a foothold at both the molecular and cellular levels has been expanded by recent investigations that have applied new technologies and used improved techniques to isolate ex vivo human tissue and generate in vitro cellular models, as well as more relevant in vivo animal challenge systems. Here, we review the current concepts of the immediate events that follow viral exposure at genital mucosal sites where most documented transmissions occur. Furthermore, we discuss the gaps in our knowledge that are relevant to future studies, which will shape strategies for effective HIV prevention.

Attachment of human immunodeficiency virus to cells and its inhibition

The entry of enveloped viruses involves virus adsorption followed by close apposition of the viral and plasma membranes. This multistep process is initiated by specific binding interactions between glycoproteins in the viral envelope and appropriate receptors on the cell surface. In the case of HIV-1, attachment of virions to the cell surface is attributed to a high affinity interaction between envelope spike glycoproteins (Env, composed of the surface protein gp120 and the transmembrane protein gp41) and a complex made of the primary CD4 receptor and a seven-transmembrane co-receptor (e.g., CXCR4 or CCR5) (reviewed in [1]). Then a chain of dynamic events take place that enable the viral nucleocapsid to penetrate within the target cell following the destabilization of membrane microenvironment and the formation of a fusion pore.

Mechanisms underlying activity of antiretroviral drugs in HIV-1-infected macrophages: new therapeutic strategies

Monocyte-derived macrophages (M/M) are considered the second cellular target of HIV-1 and a crucial virus reservoir. M/M are widely distributed in all tissues and organs, including the CNS, where they represent the most common HIV-infected cells. Differently from activated CD4+ T lymphocytes, M/M are resistant to the cytopathic effect of HIV and survive HIV infection for a long time. Moreover, HIV-1 replication in M/M is a key pathogenetic event during the course of HIV-1 infection. Overall findings strongly support the clinical relevance of anti-HIV drugs in M/M. Nucleoside RT inhibitors (NRTIs) are more active against HIV in M/M than in CD4+ T lymphocytes. Their activity is further boosted by the presence of an additional monophosphate group (i.e., a phosphonate group, as in the case of Tenofovir), thus overcoming the bottleneck of the low phosphorylation ability of M/M. In contrast, the antiviral activity of non-NRTIs (not affecting the DNA chain elongation) in M/M is similar to that in CD4+ T lymphocytes. Protease inhibitors are the only clinically approved drugs acting at a late stage of the HIV lifecycle. They are able to interfere with HIV replication in HIV-1 chronically infected M/M, even if at concentrations greater than those observed in HIV-1 chronically infected CD4+ T lymphocytes. Finally, several new drugs have been shown to interfere efficiently with HIV replication in M/M, including entry inhibitors. A better understanding of the activity of the anti-HIV drugs in M/M may represent a key element for the design of effective anti-HIV chemotherapy.

HIV interactions with dendritic cells: has our focus been too narrow?

Although few in number, dendritic cells (DCs) are heterogeneous, ubiquitous, and are crucial for protection against pathogens. In this review, the different DC subpopulations have been described and aspects of DC biology are discussed. DCs are important, not only in the pathogenesis of HIV, but also in the generation of anti-HIV immune responses. This review describes the roles that DC are thought to play in HIV pathogenesis, including uptake and transport of virus. We have also discussed the effects that the virus exerts on DCs such as infection and dysfunction. Then we proceed to focus on DC subsets in different organs and show how widespread the effects of HIV are on DC populations. It is clear that the small number of studies on tissue-derived DCs limits current research into the pathogenesis of HIV.

Reduced hematopoietic toxicity, enhanced cellular uptake and altered pharmacokinetics of azidothymidine loaded galactosylated liposomes

In order to target liposomes to the lectin receptors present on macrophages, galactosylated liposomes were prepared and characterized in vitro. O-palmitoylgalactose (OPG) for liposomal coating was synthesized by esterification of galactose with palmitoyl chloride. The galactose binding Ricinus communis lectin was employed as a model system for the determination of in vitro ligand binding capacity. Cellular drug uptake studies were performed using alveolar macrophages. Hematological changes, bone marrow toxicity, plasma and tissue distribution study of free, uncoated plain liposomal and galactosylated liposomal encapsulated azidothymidine (AZT) were determined following a bolus intravenous injection in Sprague-Dawley rats. Lectin (R. communis) carbohydrate interaction has been utilized for the effective delivery of AZT entrapped in galactosylated vesicles. Aggregation of galactosylated liposomes increased as lectin concentration was increased from 5 to 30 microg/ml. Cellular uptake of galactosylated liposomal formulation was maximum. No hematological toxicity was observed even after 10 days in case of galactosylated vesicle entrapped AZT. This formulation maintained a significant level of AZT in tissues rich in galactose specific receptors and had a prolonged residence in the body resulting in enhanced half-life of AZT. Conclusively, galactosylated liposomes are the potential candidate for targeted drug delivery and are anticipated to be promising in the treatment of AIDS6.

Therapeutic strategies towards HIV-1 infection in macrophages

It is widely recognized that macrophages (M/M) represent a crucial target of HIV-1 in the body and play a pivotal role in the pathogenic progression of HIV-1 infection. This strongly supports the clinical relevance of therapeutic strategies able to interfere with HIV-1 replication in M/M. In vitro studies showed that nucleoside analogue inhibitors of HIV-1 reverse transcriptase have potent antiviral activity in M/M, although the limited penetration of these compounds in sequestered body compartments and low phosphorylation ability of M/M, suggest that a phosphonate group linked to NRTIs may confer greater anti-HIV-1 activity in M/M. Differently, the antiviral activity of non-nucleoside reverse transcriptase inhibitors in M/M is similar to that found in CD4+ lymphocytes. Interestingly, protease inhibitors, acting at a post-integrational stage of HIV-1 life-cycle are the only drugs active in chronically infected M/M. A careful analysis of the distribution of antiviral drugs, and the assessment of their activity in M/M, represent key factors in the development of therapeutic strategies aimed to the treatment of HIV-1-infected patients. Moreover, testing new and promising antiviral compounds in such cells may provide crucial hints about their efficacy in patients infected by HIV.

Virological Synapse for Cell-Cell Spread of Viruses

Cell-to-cell spread of retroviruses via virological synapse (VS) contributes to overall progression of disease. VS are specialized pathogen-induced cellular structures that facilitate cell-to-cell transfer of HIV-1 and HTLV-1. VS provide a mechanistic explanation for cell-associated retroviral replication. While VS share some common features with neurological or immunological synapses, they also exhibit important differences. The role of VS might not be limited to human retroviruses and the emerging role of a plant synapse suggests that VS might well be conserved structures for cell-cell spreading of both animal and plant viruses. Dissection of the VS is just at its beginning, but already offers ample information and fascinating insights into mechanisms of viral replication and cell-to-cell communication.

Limited development and progression of resistance of HIV-1 to the nucleoside analogue reverse transcriptase inhibitor lamivudine in human primary macrophages

OBJECTIVES

The aim of this study was to investigate the development and progression of phenotypic resistance to the HIV-1-reverse transcriptase (RT) inhibitor lamivudine, and genotypic variations of HIV-1-RT occurring under lamivudine treatment in HIV-1-infected human primary monocytes-macrophages (M/M).

METHODS

Cellular passages in the presence of lamivudine were performed every 2 weeks by transferring supernatants of infected M/M to fresh M/M. A fitness assay using wild-type virus and a lamivudine-resistant HIV-1 virus (harbouring the M184V RT mutation) was performed in peripheral blood mononuclear cells. Culture supernatants were tested for p24 antigen production and RT activity. The M184V RT mutant virus was obtained by site-directed mutagenesis on a CCR5-using HIV-1 backbone.

RESULTS

The mutagenized M184V RT virus showed full resistance to lamivudine in M/M. However, no detectable phenotypic and genotypic resistance (neither virus breakthrough, nor RT resistance-related mutations) developed in M/M infected by HIV-1 and cultured for up to seven passages in vitro (i.e. 105 days). This inefficiency of M/M to develop M184V RT mutated virus is tightly related to the low 2'-deoxynucleotide (dNTP) pool in such cells, which in turn decreases the kinetics of HIV-1-RT. Despite this, the M184V RT mutant virus replicates in M/M, although with a 30% decreased efficiency compared with the wild-type.

CONCLUSIONS

Our results show that the chances of development of resistance are far lower in M/M than in lymphocytes. This underlines the importance and the peculiar role of M/M as reservoirs of either wild-type or resistant strains in human organs.

Mechanisms promoting dendritic cell-mediated transmission of HIV

Dendritic cells (DC) survey epithelial or mucosal surfaces for antigens, take them up via their endocytic or phagocytic receptors, process the captured antigens and migrate to the lymphatic tissues. In the draining lymph nodes they present the immunogenic peptides to T cells thereby inducing antigen-specific immune responses. HIV-1 in turn seems to have developed mechanisms to exploit the natural trafficking of DC to establish infection in its primary targets, the CD4+ T cells. This review discusses several aspects of DC-HIV interactions with a main focus on the attachment, internalisation and transmission of the virus by DC to cells, susceptible for infection with HIV.

HIV-1 and the hijacking of dendritic cells: a tug of war

Dendritic cells are critical for host immunity and are involved both in the innate and adaptive immune responses. They are among the first cells targeted by HIV-1 in vivo at mucosal sites. Dendritic cells can sequester HIV-1 in endosomal compartments for several days and transmit infectious HIV-1 to interacting T cells in the lymph node, which is the most important site for viral replication and spread. Initially, the cellular immune response developed against HIV-1 is strong, but eventually it fails to control and resolve the infection. The most dramatic effect seen on the immune system during untreated HIV-1 infection is the destruction of helper CD4(+) T cells, which leads to subsequent immune deficiency. However, the immunomodulatory effects of HIV-1 on different dendritic cell subpopulations may also play an important role in the pathogenesis of HIV-1. This review discusses the effects HIV-1 exerts on dendritic cells in vivo and in vitro, including the binding and uptake of HIV by dendritic cells, the formation of infectious synapses, infection, and the role of dendritic cells in HIV-1 pathogenesis.

Dangerous liaisons at the virological synapse

Cell-to-cell viral transmission facilitates the propagation of HIV-1 and human T cell leukemia virus type 1. Mechanisms of cell-to-cell transmission by retroviruses were not well understood until the recent description of virological synapses (VSs). VSs function as specialized sites of immune cell-to-cell contact that direct virus infection. Deciphering the molecular mechanisms of VS formation provides a fascinating insight into how pathogens subvert immune cell communication programs and achieve viral spread.

Normal skin of HIV-infected individuals contains increased numbers of dermal CD8 T cells and normal numbers of Langerhans cells

Dysregulation of the skin immune system (SIS) could explain the high prevalence of skin disorders in HIV+ individuals. The present study was carried out to determine whether alterations in the cell population of SIS and epidermal immunoactivation occur in the normal skin of HIV+ individuals. Forty-five biopsies were taken from the normal upper arm skin of 45 HIV+ patients and of 15 healthy controls. HIV+ individuals were divided into three categories according to their CD4 cell blood count (<200, 200-499 and > or = 500/microl). Hematoxylin-eosin was used to stain tissue sections for morphological analysis and immunohistochemistry was used for the evaluation of the frequency of macrophages, Langerhans cells, and CD lymphocyte subsets. In addition, semiquantitative analysis of LFA-1, ICAM-1 and HLA-DR was determined in epidermal cells. Macrophages, Langerhans cells, and CD lymphocyte subsets did not differ significantly between any of the patient categories and the control group. When all HIV+ individuals were compared as a group to the control group, a significant increase in dermal CD8+ T lymphocytes (P < 0.01) and lower CD4-CD8 ratios (P < 0.01) were observed in the HIV+ individuals. Epidermal ICAM-1 and HLA-DR expression was negative in both HIV+ and normal skin biopsies. No evidence of a depletion of the SIS population or of epidermal immunoactivation in normal skin from HIV+ individuals was demonstrable, suggesting that alterations in the central immune system are not necessarily reflected in the SIS of HIV-infected patients.

The interaction of immunodeficiency viruses with dendritic cells

Dendritic cells (DCs) can influence HIV-1 and SIV pathogenesis and protective mechanisms at several levels. First, HIV-1 productively infects select populations of DCs in culture, particularly immature DCs derived from blood monocytes and skin (Langerhans cells). However, there exist only a few instances in which HIV-1- or SIV-infected DCs have been identified in vivo in tissue sections. Second, different types of DCs reliably sequester and transmit infectious HIV-1 and SIV in culture, setting up a productive infection in T cells interacting with the DCs. This stimulation of infection in T cells may explain the observation that CD4+ T lymphocytes are the principal cell type observed to be infected with HIV-1 in lymphoid tissues in vivo. DCs express a C-type lectin, DC-SIGN/CD209, that functions to bind HIV-1 (and other infectious agents) and transmit virus to T cells. When transfected into the THP-1 cell line, the cytosolic domain of DC-SIGN is needed for HIV-1 sequestration and transmission. However, DCs lacking DC-SIGN (Langerhans cells) or expressing very low levels of DC-SIGN (rhesus macaque monocyte-derived DCs) may use additional molecules to bind and transmit immunodeficiency viruses to T cells. Third, DCs are efficient antigen-presenting cells for HIV-1 and SIV antigens. Infection with several recombinant viral vectors as well as attenuated virus is followed by antigen presentation to CD4+ and CD8+ T cells. An intriguing pathway that is well developed in DCs is the exogenous pathway for nonreplicating viral antigens to be presented on class I MHC products. This should allow DCs to stimulate CD8+ T cells after uptake of antibody-coated HIV-1 and dying infected T cells. It has been proposed that DCs, in addition to expanding effector helper and killer T cells, induce tolerance through T cell deletion and suppressor T cell formation, but this must be evaluated directly. Fourth, DCs are likely to be valuable in improving vaccine design. Increasing DC uptake of a vaccine, as well as increasing their numbers and maturation, should enhance efficacy. However, DCs can also capture antigens from other cells that are initially transduced with a DNA vaccine or a recombinant viral vector. The interaction of HIV-1 and SIV with DCs is therefore intricate but pertinent to understanding how these viruses disrupt immune function and elicit immune responses.

The role of dendritic cells in the pathogenesis of HIV-1 infection

Dendritic cells are professional antigen-presenting cells required for generation of adaptive immunity. These cells are one of the initial target cells for HIV-1 infection or capture of virions at site of transmission in the mucosa. DCs carrying HIV-1 will migrate to the lymphoid tissue where they can contribute to the dissemination of the virus to adjacent CD4+ T cells. In addition, HIV-1-exposed DCs may have impaired antigen-presenting capacity resulting in inadequate expansion of HIV-1-specific T cell responses. Here, we review the infection of different subtypes of DCs by HIV-1 and the relevance of these cells in the transmission and establishment of HIV-1 disease. In addition, we discuss the mechanisms through which HIV-1-DC interactions could be exploited to optimise the generation and maintenance of HIV-1-specific T cell immunity.

HIV-1 pathogenesis

Despite considerable advances in HIV science in the past 20 years, the reason why HIV-1 infection is pathogenic is still debated and the goal of eradicating HIV-1 infection remains elusive. A deeper understanding of the interplay between HIV-1 and its host and why simian immunodeficiency virus (SIV) is nonpathogenic in some natural hosts may provide a few answers.

Potential role for CD63 in CCR5-mediated human immunodeficiency virus type 1 infection of macrophages

Macrophages and CD4(+) lymphocytes are the principal target cells for human immunodeficiency virus type 1 (HIV-1) infection, but the molecular details of infection may differ between these cell types. During studies to identify cellular molecules that could be involved in macrophage infection, we observed inhibition of HIV-1 infection of macrophages by monoclonal antibody (MAb) to the tetraspan transmembrane glycoprotein CD63. Pretreatment of primary macrophages with anti-CD63 MAb, but not MAbs to other macrophage cell surface tetraspanins (CD9, CD81, and CD82), was shown to inhibit infection by several R5 and dualtropic strains, but not by X4 isolates. The block to productive infection was postfusion, as assessed by macrophage cell-cell fusion assays, but was prior to reverse transcription, as determined by quantitative PCR assay for new viral DNA formation. The inhibitory effects of anti-CD63 in primary macrophages could not be explained by changes in the levels of CD4, CCR5, or beta-chemokines. Infections of peripheral blood lymphocytes and certain cell lines were unaffected by treatment with anti-CD63, suggesting that the role of CD63 in HIV-1 infection may be specific for macrophages.

Target cells in vaginal HIV transmission

Understanding the mechanisms of HIV transmission to women will be crucial to the development of effective strategies to curb this epidemic. Current data suggest that HIV has at least two routes to penetrate the vaginal epithelium and reach lymphoid tissues, trans-epithelial migration of infected Langerhans cells or virus penetration into the lamina propria through loss of epithelial integrity resulting in direct infection of lymphocytes, dendritic cells and macrophages.

Long-term survival and virus production in human primary macrophages infected by human immunodeficiency virus

The role of macrophages in the pathogenesis and progression of human immunodeficiency virus (HIV)-related infection is substantiated by in vitro and in vivo evidence. The unique ability to survive HIV infection and produce viral particles for long periods is postulated. Detailed studies of this phenomenon are lacking. The dynamics of HIV-1 replication and cumulative virus production was studied in long-term cultures of macrophages in the presence or in the absence of antiviral drugs. Multiply spliced and unspliced HIV-RNA production was assessed by quantitative PCR, and the number of infected cells was monitored by FACS analysis. Cumulative HIV-1 production was determined by a trapezoidal equation, including such parameters as times of collection and experimental values of genomic-RNA and p24 gag antigen. Unspliced and multiply spliced HIV-RNA increased linearly after macrophage infection; reached levels of 1.5 x 10(8) and 2.8 x 10(5) copies/10(5) cells, respectively, at day 10; and then remained stable throughout the course of the experiment. Cumulative production of genomic-RNA and p24 gag antigen was 10(10) copies/10(6) cells and 10(7) pg/10(6) cells, respectively, with an average of >200 virus particles produced daily by each macrophage. AZT decreased the cumulative production of both genomic-RNA and p24 gag antigen down to 2.5 x 10(9) copies and 1.1 x 10(6) pg/10(6) cells (73.8% and 88.9% inhibition, respectively) up to day 50 without virus breakthrough. Ritonavir had a limited, but consistent, efficacy on the release of mature virus proteins (about 40% inhibition), but not on HIV-RNA production. In conclusion, the long-term dynamics and the high cumulative virus production that characterize HIV-1 infection of macrophages underscore the peculiar role of these cells as a persistently infected reservoir of HIV.

Macrophages and HIV infection: therapeutical approaches toward this strategic virus reservoir

Cells of macrophage lineage represent a key target of human immunodeficiency virus (HIV) in addition to CD4-lymphocytes. The absolute number of infected macrophages in the body is relatively low compared to CD4-lymphocytes. Nevertheless, the peculiar dynamics of HIV replication in macrophages, their long-term survival after HIV infection, and their ability to spread virus particles to bystander CD4-lymphocytes, make evident their substantial contribution to the pathogenesis of HIV infection. In addition, infected macrophages are able to recruit and activate CD4-lymphocytes through the production of both chemokines and virus proteins (such as nef). In addition, the activation of the oxidative pathway in HIV-infected macrophages may lead to apoptotic death of bystander, not-infected cells. Finally, macrophages are the most important target of HIV in the central nervous system. The alteration of neuronal metabolism induced by infected macrophages plays a crucial role in the pathogenesis of HIV-related encephalopathy. Taken together, these results strongly support the clinical relevance of therapeutic strategies able to interfere with HIV replication in macrophages. In vitro data show the potent efficacy of all nucleoside analogues inhibitors of HIV-reverse transcriptase in macrophages. Nevertheless, the limited penetration of some of these compounds in sequestered districts, coupled with the scarce phosphorylation ability of macrophages, suggests that nucleoside analogues carrying preformed phosphate groups may have a potential role against HIV replication in macrophages. This hypothesis is supported by the great anti-HIV activity of tenofovir and other acyclic nucleoside phosphonates in macrophages that may provide a rationale for the remarkable efficacy of tenofovir in HIV-infected patients. Non-nucleoside reverse transcriptase inhibitors (NNRTI) do not affect HIV-DNA chain termination, and for this reason their antiviral activity in macrophages is similar to that found in CD4-lymphocytes. Interestingly, protease inhibitors (PIs), acting at post-integrational stages of virus replication, are the only drugs able to interfere with virus production and release from macrophages with established and persistent HIV infection (chronically-infected cells). Since this effect is achieved at concentrations and doses higher than those effective in de-novo infected CD4-lymphocytes, it is possible that lack of adherence to therapy, and/or suboptimal dosage leading to insufficient concentrations of PIs may cause a resumption of virus replication from chronically-infected macrophages, ultimately resulting in therapeutic failure. For all these reasons, therapeutic strategies aimed to achieve the greatest and longest control of HIV replication should inhibit HIV not only in CD4-lymphocytes, but also in macrophages. Testing new and promising antiviral compounds in such cells may provide crucial hints about their efficacy in patients infected by HIV.

Essential roles for dendritic cells in the pathogenesis and potential treatment of HIV disease

During sexual transmission of HIV, virus crosses mucosal epithelium and eventually reaches lymphoid tissue where it establishes a permanent infection. Evidence has accumulated that infection of Langerhans cells, which are resident dendritic cells in pluristratified epithelia, plays a crucial role in the early events of HIV transmission. HIV infection of Langerhans cells is regulated by surface expression of CD4 and CCR5. Thus, topical microbicides that interfere with HIV infection of Langerhans cells represent an attractive strategy for blocking sexual transmission of virus. Capture and uptake of HIV virions is another major pathway by which HIV interacts with dendritic cells. By contrast, this process is mediated by a newly described C-type lectin, DC-SIGN. It is well established that HIV-exposed dendritic cells transmit virus efficiently to cocultured T cells. Indeed, dendritic cell-T cell interaction, critical in the generation of immune responses, is a rich microenvironment for HIV replication both in vitro and in vivo. Dendritic cells that have captured virus via DC-SIGN, and not HIV-infected dendritic cells, probably facilitate most infection of T cells in chronically infected individuals. Therefore, blocking DC-SIGN-mediated capture of HIV represents a potential therapeutic antiviral strategy for HIV disease. Lastly, dendritic cells have been targeted both ex vivo and in vivo to initiate and enhance HIV-specific immunity. Although these approaches are promising for both therapeutic and prophylactic vaccines, much additional work is needed in order to optimize dendritic-cell-based immunization strategies.

Cutaneous dendritic cells are main targets in acute HIV-1-infection

Acute human immunodeficiency virus (HIV) infection is a transient illness that typically presents with mucocutaneous and constitutional symptoms. It is soon followed by seroconversion with the detection of anti-HIV antibodies in the peripheral blood. To better understand the pathogenetic events leading to this clinical picture, we sought to investigate the (immuno)histologic features of the skin rash occurring in an acutely infected person. A skin biopsy of an acutely infected person was investigated histologically and immunohistologically using paraffin-embedded tissue sections. Interface dermatitis with pronounced vacuolization of the basal keratinocytes was a prominent histological finding. The inflammatory infiltrate was composed of CD3+/CD8+ T cells with coexpression of Granzyme B7 and TIA-1, and CD68+ histiocytes/dendritic cells. CD1a+ intraepidermal Langerhans cells (LC) were significantly decreased and individual LC coexpressed HIV-p24 antigens as evidenced in double labeling experiments. HIV-infected LC were demonstrated in close apposition to cytotoxic T cells. This study provides the first definitive evidence for infection of LC at extramucosal sites in this very early stage of disease. Our findings emphasize the critical role of dendritic cells as a virus reservoir and the skin as a major site of HIV replication during the course of the disease.

Exposure of normal monocyte-derived dendritic cells to human immunodeficiency virus type-1 particles leads to the induction of apoptosis in co-cultured CD4+ as well as CD8+ T cells

The depletion of immune T cells by human immunodeficiency virus type-1 (HIV-1) infection is a major mechanism involved in the pathogenesis of AIDS. Here, we examined a possible effector function of blood monocyte-derived dendritic cells (DCs) to induce apoptosis in bystander CD4+ and CD8+ T cells. The DCs were generated by culturing monocytes in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4. The DCs exposed to HIV-1 particles were co-cultured with healthy donor-derived blood T cells at a ratio of 1:20. Analyses by percent cell mortality, staining with propidium iodide and reactivity with Annexin V revealed the induction of apoptosis in both CD4+ and CD8+ target T cells. Further, this apoptosis occurred without stimulation with mitogens when the cell cycle of target T cells shifted from G0 to G1, probably due to the mitogenic effect of the DCs. Thus, induction of apoptosis in both CD4+ and CD8+ T cells occurred via interaction with DCs adsorbed with HIV-1 particles.

HIV-infected human Langerhans cells transmit infection to human lymphoid tissue ex vivo

OBJECTIVES

To create a novel ex vivo model for early biologic events involved in sexual transmission of HIV and to demonstrate that Langerhans cells (LC), the purported initial mucosal target cells for HIV, play a critical role in this process.

METHODS

Epidermal cells containing LC were isolated from normal-appearing skin of healthy volunteers and exposed to a panel of primary and laboratory-adapted R5- and X4-HIV isolates, washed and applied to the surfaces of allogeneic tonsil tissue blocks. Viral replication was followed by measuring HIV p24 protein in culture supernatants by ELISA.

RESULTS

Both R5- and X4-HIV isolates could be transmitted by LC and established high levels of infection in lymphoid tissue (p24 > 10 ng/ml). Depletion of LC within epidermal cell suspensions abrogated the ability of HIV-exposed suspensions to transmit virus to tonsil histocultures.

CONCLUSIONS

Using a novel ex vivo model, human LC are shown for the first time to be the major epidermal cell type that is involved in transmission of HIV infection to human lymphoid tissue. Importantly, this system could prove useful in further understanding LC trafficking and other early biological events involved in primary HIV infection.

Nerve growth factor is an autocrine factor essential for the survival of macrophages infected with HIV

Nerve growth factor (NGF) is a neurotrophin with the ability to exert specific effects on cells of the immune system. Human monocytes/macrophages (M/M) infected in vitro with HIV type 1 (HIV-1) are able to produce substantial levels of NGF that are associated with enhanced expression of the high-affinity NGF receptor (p140 trkA) on the M/M surface. Treatment of HIV-infected human M/M with anti-NGF Ab blocking the biological activity of NGF leads to a marked decrease of the expression of p140 trkA high-affinity receptor, a concomitant increased expression of p75(NTR) low-affinity receptor for NGF, and the occurrence of apoptotic death of M/M. Taken together, these findings suggest a role for NGF as an autocrine survival factor that rescues human M/M from the cytopathic effect caused by HIV infection.

A rational basis for mucosal vaccination against HIV infection

The lack of success in the development of an effective conventional vaccine against HIV has focused attention on mucosal immunity. This is a rational move, since HIV is transmitted mostly by the mucosal route. The mucosal strategy is based on the concept that: a) HIV/SIV has to cross the mucosal-regional lymph node-blood barriers, each of which can prevent viral transmission or decrease the viral load. b) Immunization has to target directly the mucosal tissues or indirectly the regional lymph nodes, in order to prevent or control viral replication. This strategy is consistent with antigen localization and effective entry into the lymph nodes, driving the immune response. c) A dual immune mechanism may be necessary for effective mucosal protection, mediated by specific CD4 and CD8 T-cell and antibody responses to the immunizing antigens, and innate antiviral factors and beta-chemokines which down-modulate CCR5 co-receptors. Targeted iliac lymph node immunization with SIVgp120 and p27 in alum prevents SIV infection or significantly decreases the viral load when challenged by the rectal route. Indeed, in addition to specific immunity, including significant sIgA antibody-forming cells in the iliac lymph nodes, CD8-suppressor factor and the three beta-chemokines (RANTES, macrophage inflammatory protein (MIP)-1 alpha and MIP-1 beta) are significantly associated with protection against rectal mucosal SIV infection.

The Susceptibility to X4 and R5 Human Immunodeficiency Virus-1 Strains of Dendritic Cells Derived In Vitro From CD34+ Hematopoietic Progenitor Cells Is Primarily Determined by Their Maturation Stage

Dendritic cells (DC) were sorted on day 8 from cultures of CD34+ cells with stem cell factor/Flt-3 ligand/ granulocyte-macrophage colony-stimulating factor (GM-CSF)/tumor necrosis factor- (TNF-)/interleukin-4 (IL-4). Exposing immature CCR5+CXCR4lo/− DC to CCR5-dependent human immunodeficiency virus (HIV)-1Ba-L led to productive and cytopathic infection, whereas only low virus production occurred in CXCR4-dependent HIV-1LAI–exposed DC. PCR analysis of the DC 48 hours postinfection showed efficient entry of HIV-1Ba-L but not of HIV-1LAI. CD40 ligand- or monocyte-conditioned medium-induced maturation of HIV-1Ba-L–infected DC reduced virus production by about 1 Log, while cells became CCR5−. However, HIV-1Ba-L–exposed mature DC harbored 15-fold more viral DNA than their immature counterparts, ruling out inhibition of virus entry. Simultaneously, CXCR4 upregulation by mature DC coincided with highly efficient entry of HIV-1LAI which, nonetheless, replicated at the same low level in mature as in immature DC. In line with these findings, coculture of HIV-1Ba-L–infected immature DC with CD3 monoclonal antibody–activated autologous CD4+ T lymphocytes in the presence of AZT decreased virus production by the DC. Finally, whether they originated from CD1a+CD14− or CD1a−CD14+ precursors, DC did not differ as regards permissivity to HIV, although CD1a+CD14− precursor-derived immature DC could produce higher HIV-1Ba-L amounts than their CD1a−CD14+ counterparts. Thus, both DC permissivity to, and capacity to support replication of, HIV is primarily determined by their maturation stage.