Interaction of human epidermal Langerhans cells with HIV-1 viral envelope proteins (gp 120 and gp 160s) involves a receptor-mediated endocytosis independent of the CD4 T4A epitope

Human immunodeficiency virus-1 uses the mannose-6-phosphate receptor to cross the blood-brain barrier

HIV-1 circulates both as free virus and within immune cells, with the level of free virus being predictive of clinical course. Both forms of HIV-1 cross the blood-brain barrier (BBB) and much progress has been made in understanding the mechanisms by which infected immune cells cross the blood-brain barrier BBB. How HIV-1 as free virus crosses the BBB is less clear as brain endothelial cells are CD4 and galactosylceramide negative. Here, we found that HIV-1 can use the mannose-6 phosphate receptor (M6PR) to cross the BBB. Brain perfusion studies showed that HIV-1 crossed the BBB of all brain regions consistent with the uniform distribution of M6PR. Ultrastructural studies showed HIV-1 crossed by a transcytotic pathway consistent with transport by M6PR. An in vitro model of the BBB was used to show that transport of HIV-1 was inhibited by mannose, mannan, and mannose-6 phosphate and that enzymatic removal of high mannose oligosaccharide residues from HIV-1 reduced transport. Wheatgerm agglutinin and protamine sulfate, substances known to greatly increase transcytosis of HIV-1 across the BBB in vivo, were shown to be active in the in vitro model and to act through a mannose-dependent mechanism. Transport was also cAMP and calcium-dependent, the latter suggesting that the cation-dependent member of the M6PR family mediates HIV-1 transport across the BBB. We conclude that M6PR is an important receptor used by HIV-1 to cross the BBB.

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.

TGFβ Inhibits CD1d Expression on Dendritic Cells

The CD1 family of cell surface glycoprotein has been demonstrated to be a third lineage of antigen-presenting molecules for specific T cell responses. They present lipidic, glycolipidic antigen and hydrophobic peptide to T cells. CD1d restricted T cells play a role in autoimmune disease and in tumor immunity. Transforming growth factor beta (TGFbeta), a member of the family of polypeptide growth factors synthetized by human keratinocytes, has inhibitory effects on proliferation and differentiation of immune cells, especially on CD1d-restricted natural killer T cells. These properties led us to investigate the role of TGFbeta in CD1d expression on dendritic cells (DC), which are known to play a key role in initiation of the immune response. Here, we observed CD1d molecules on DC developed from PBMC with GM-CSF and IL4 but not with GM-CSF, IL4 and TGFbeta for 7 d. RT-PCR and FACS analysis (mAb 42.1) performed at various stages of differentiation on CD34+ HPC show that CD1d mRNA levels and CD1d molecule expression at the cell surface decreased progressively during the differentiation process. Thus, while committing DC-precursors differentiation toward the Langerhans cell (LC) pathway, TGFbeta likely inhibits CD1d transcription. Therefore, LC freshly recovered from epidermal sheet were evaluated by flow cytometry. In accordance with in vitro observation, they did not expressed measurable levels of CD1d molecules at the cell membrane. Thus, TGFbeta produced by keratinocytes contribute to selectively downregulate CD1d expression on intraepidermal-resident LC.

Diversity of receptors binding HIV on dendritic cell subsets

The ability of HIV-1 to use dendritic cells (DCs) for transport and to transfer virus to activated T cells in the lymph node may be crucial in early HIV-1 pathogenesis. We have characterized primary DCs for the receptors involved in viral envelope attachment and observed that C-type lectin receptor (CLR) binding was predominant in skin DCs, whereas binding to emigrating and tonsil DCs was CD4-dependent. No one CLR was solely responsible for envelope binding on all skin DC subsets. DC-SIGN (DC-specific ICAM-3-grabbing nonintegrin) was only expressed by CD14(+)CDla(lo) dermal DCs. The mannose receptor was expressed by CD1a(hi) and CD14(+)CDla(lo) dermal DCs, and langerin was expressed by Langerhans cells. The diversity of CLRs able to bind HIV-1 in skin DCs may reflect their ability to bind a range of microbial glycoproteins.

Bitter-sweet symphony: defining the role of dendritic cell gp120 receptors in HIV infection

BACKGROUND

Dendritic cells (DC) are believed to be one of the first cell types infected during HIV transmission. Recently a single C-type lectin receptor (CLR), DC-SIGN, has been reported to be the predominant receptor on monocyte derived DC (MDDC) rather than CD4. The role of other CLRs in HIV binding and HIV binding by CLRs on other types of DC in vivo is largely unknown.

OBJECTIVES AND STUDY DESIGN

Review HIV binding to DC populations, both in vitro and in vivo, in light of the immense interest of a recently re-identified CLR called DC-SIGN.

RESULTS AND CONCLUSIONS

From recent work, it is clear that immature MDDC have a complex pattern of HIV gp120 binding. In contrast to other cell types gp120 has the potential to bind to several receptors on DC including CD4 and several types of C type lectin receptor, not just exclusively DC-SIGN. Given the diverse types of DC in vivo future work will need to focus on defining the receptors for HIV binding to these different cell types. Mucosal transmission of HIV in vivo targets immature sessile DCs, including Langerhans cells which lack DC-SIGN. The role of CLRs and DC-SIGN in such transmission remains to be defined.

Role of dendritic cells in immunopathogenesis of human immunodeficiency virus infection

The role of dendritic cells (DC) in the pathogenesis of human immunodeficiency virus (HIV) disease has been a subject of considerable interest for several years. Initial studies focused on the infection, dysfunction, and depletion of DC in HIV-infected individuals. More recent studies have begun to identify the functional role of DC in the initiation and propagation of viral replication in T cells in HIV-infected individuals. This review discusses recent data regarding the role of DC in HIV disease with the aim of delineating basic immunopathogenic principles of infection and the development of therapeutic strategies.

The skin as target, vector, and effector organ in human immunodeficiency virus disease

Langerhans cells are CD4+ antigen-presenting cells in the dendritic cell family that can initiate primary and secondary immune responses after emigration from skin and mucosa. Because of these properties, Langerhans cells have been proposed as potential targets for human immunodeficiency virus (HIV) infection and as potential vectors for the transmission of primary HIV infection to T cells after mucosal exposure. In support of this theory, previous investigative studies have demonstrated that Langerhans cells are targets for HIV infection both in vivo and in vitro and that HIV-pulsed Langerhans cells, as well as blood dendritic cells, induce a productive infection in co-cultured T cells in vitro. In addition, Langerhans cell dysfunction has been proposed as contributing to the pathogenesis of some of the cutaneous manifestations observed in HIV+ individuals. In a recent study, we detected Langerhans cell dysfunction in patients with acquired immune deficiency syndrome, but not in earlier stages of HIV disease. Here we review previous and current investigative studies on HIV and the skin, with an emphasis on Langerhans cells, and discuss possible future investigations in this field.

Detection of HIV-specific DNA sequences in epidermal Langerhans cells infected in vitro by means of a cell-free system

As dendritic antigen-presenting cells in skin and mucous membranes, Langerhans cells (LC) are found in areas at risk of inoculation by the human immunodeficiency virus (HIV). LC have been reported as targets for HIV-1. The aim of the present study was to investigate whether LC can be experimentally infected by HIV provided by a cell-free infection system. A cell-free suspensions was prepared from viral particles provided by chronically infected cell lines (U937 or H9 cells) by low-speed centrifugation followed by 0.45-microns filtration. LC-enriched epidermal cell (EC) suspensions with no CD3+ cells (assessed by flow cytometry and electron microscopy) and uninfected U937 cells (cell-free infection system control) were infected with two isolates (HTL VIII-B and RF). The infectiousness of the cell-free virus fluids was controlled on U937 cells where proviral DNA was amplified (gag, pol, and env gene sequences by the polymerase chain reaction, PCR) and release of virus particles into the supernatant was controlled either by measure of the reverse transcriptase (RT) activity or detection of viral RNA amplified by RT-PCR for the gag gene sequences). Proviral DNA (gag gene sequences) was found in LC-enriched epidermal cellular DNA from day 4 post-infection with isolate HTL VIII-B and from day 7 with isolate RF. Although the RT activity did not reach a significantly high level, viral RNA was found in the supernatant of LC-enriched EC cultures at the same time as proviral DNA was detected in LC.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of Langerhans cells and other dendritic cells in viral diseases

Langerhans cells are part of a vast system of potent antigen-presenting cells known under the name of dendritic cells. During the last decade, much has been learned on dendritic cell involvement in the immune response to infectious diseases. This review briefly summarizes our current understanding of the role played by Langerhans cells and other dendritic cells in the pathogenesis of DNA and RNA virus infections. These data may form the basis for the development of innovative approaches in the diagnosis, prevention, and treatment of viral diseases.