Dendritic cells from HIV-1 infected individuals show reduced capacity to stimulate autologous T-cell proliferation

Dendritic cells in progression and pathology of HIV infection

Although the major targets of HIV infection are CD4⁺ T cells, dendritic cells (DCs) represent a crucial subset in HIV infection because they influence viral transmission and target cell infection and presentation of HIV antigens. DCs are potent antigen-presenting cells that can modulate antiviral immune responses. Through secretion of inflammatory cytokines and interferons (IFNs), DCs also alter T cell proliferation and differentiation, participating in the immune dysregulation characteristic of chronic HIV infection. Their wide distribution in close proximity with the mucosal epithelia makes them one of the first cell types to encounter HIV during sexual transmission. We discuss here the multiple roles that DCs play at different stages of HIV infection, emphasizing their relevance to HIV pathology and progression.

The effect of human immunodeficiency virus-1 on monocyte-derived dendritic cell maturation and function

Dendritic cells (DC) are mediators of the adaptive immune response responsible for antigen presentation to naive T cells in secondary lymph organs. Human immunodeficiency virus (HIV-1) has been reported to inhibit the maturation of DC, but a clear link between maturation and function has not been elucidated. To understand further the effects of HIV-1 on DC maturation and function, we expanded upon previous investigations and assessed the effects of HIV-1 infection on the expression of surface molecules, carbohydrate endocytosis, antigen presentation and lipopolysaccharide (LPS) responsiveness over the course of maturation. In vitro infection with HIV-1 resulted in an increase in the expression of DC-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) as well as decreases in maturation-induced CCR7 and major histocompatibility complex (MHC)-II expression. Retention of endocytosis that normally occurs with DC maturation as well as inhibition of antigen presentation to CD8(+) T cells was also observed. Mitogen-activated protein kinase (MAPK) responsiveness to LPS as measured by phosphorylation of p38, c-Jun N-terminal kinase (JNK) and extracellular-regulated kinase (ERK)1/2 was not affected by HIV-1 infection. In summary, in-vitro HIV-1 impairs DC maturation, as defined by cell surface protein expression, with selective alterations in mature DC function. Understanding the mechanisms of DC dysfunction in HIV infection will provide further insight into HIV immune pathogenesis.

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.

Equine infectious anemia virus-infected dendritic cells retain antigen presentation capability

To determine if equine monocyte-derived dendritic cells (DC) were susceptible to equine infectious anemia virus (EIAV) infection, ex vivo-generated DC were infected with virus in vitro. EIAV antigen was detected by immunofluorescence 3 days post-infection with maximum antigen being detected on day 4, whereas there was no antigen detected in DC incubated with the same amount of heat-inactivated EIAV. No cytolytic activity was observed after EIAV(WSU5) infection of DC. These monocyte-derived DC were more effective than macrophages and B cells in stimulating allogenic T lymphocytes. Both infected macrophages and DC stimulated similar levels of memory CTL responses in mixtures of CD8+ and CD4+ cells as detected with (51)Cr-release assays indicating that EIAV infection of DC did not alter antigen presentation. However, EIAV-infected DC were more effective than infected macrophages when used to stimulate memory CTL in isolated CD8+ cells. The maintenance of antigen processing and presenting function by EIAV-infected DC in vitro suggests that this function is maintained during in vivo infection.

In vitro maturation potential of monocyte-derived dendritic cells is impaired in patients with spinal cord injury: a case-control study

OBJECTIVE

To determine whether the T-cell reactivity and maturation potential of dendritic cells are impaired in subjects with spinal cord injury (SCI).

DESIGN

Cross-sectional, case-control study.

SETTING

University hospital in Taiwan.

PARTICIPANTS

Thirty male SCI subjects, including 14 with paraplegia and 16 with tetraplegia, and 30 age- and sex-matched healthy controls.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

CD4+ and CD8+ T-cell reactivity was assessed by lymphoproliferative response (LPR) and CD69 expression in response to stimulation with antigens, anti-CD3 monoclonal antibody, and mitogen. Dendritic cell maturation potential was assessed by phenotypic (CD80 and CD83 expression in stimulated monocyte-derived dendritic cells) and functional (the LPR of alloreactive T cells in mixed leukocyte reactions) analysis.

RESULTS

The potential of phenotypic and functional maturation of dendritic cells of subjects with SCI was significantly impaired compared with healthy controls, and that potential was worse for tetraplegic patients than for paraplegic patients. However, no significant difference was found in T-cell responses of CD4+ and CD8+ subsets between subjects with SCI and healthy controls.

CONCLUSIONS

Impaired maturation potential of dendritic cells is a novel defect in innate immunity in people with SCI.

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.

Bone marrow-derived dendritic cells, infection with human immunodeficiency virus, and immunopathology

Dendritic cells (DC) exposed to HIV-1 show nonproductive infection that may become productive as they mature. The distribution of DC within genital mucosa and their susceptibility to infection particularly with clade E viruses could be reflected in the ease of heterosexual transmission. Carriage of virus and viral antigen by DC into lymph nodes may allow clustering and activation of T cells and production of protective immune responses. However, secondary infection of activated T cells from infected DC could cause dissemination of virus and loss of infected DC and T cells. In asymptomatic infection, fewer dendritic cells with reduced capacity to stimulate CD4 T cell proliferation are found before evidence of T cell abnormalities, and these early changes in antigen-presenting cells may result in a decline in the production of CD4 memory T cells. However, DC fuel ongoing production of antibody to HIV-1. Signaling by DC to T cells may thus underlie two major features of early HIV infection--loss in CD4+ memory T cells and persistence of antibody production. In AIDS, infected dendritic and epithelial cells within the thymus may affect maturation and contribute to loss of the "naive" T cell population. Further loss of memory T cells may occur through syncytium formation with infected DC. Finally, in AIDS patients, there is a failure in the development and the function of DC from CD34+ stem cells. In conclusion, the infection of dendritic cells, loss in their numbers, and changed signaling to T cells may shape the pattern of immunity during infection with HIV-1. Conversely, treatments that reverse the defect in antigen presentation by DC may improve cell-mediated immunity.