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Chemokine receptor type 6 (CCR6)⁺CD4⁺ T cells are preferentially infected and depleted during HIV disease progression, but are preserved in non-progressors. CCR6 is expressed on a heterogeneous population of memory CD4⁺ T cells that are critical to mucosal immunity. Preferential infection of these cells is associated, in part, with high surface expression of CCR5, CXCR4, and α4β7. In addition, CCR6⁺CD4⁺ T cells harbor elevated levels of integrated viral DNA and high levels of proliferation markers. We have previously shown that the CCR6 ligands MIP-3α and human beta defensins inhibit HIV replication. The inhibition required CCR6 and the induction of APOBEC3G. Here, we further characterize the induction of apolipoprotein B mRNA editing enzyme (APOBEC3G) by human beta defensin 2. Human beta defensin 2 rapidly induces transcriptional induction of APOBEC3G that involves extracellular signal-regulated kinases 1/2 (ERK1/2) activation and the transcription factors NFATc2, NFATc1, and IRF4. We demonstrate that human beta defensin 2 selectively protects primary CCR6⁺CD4⁺ T cells infected with HIV-1. The selective protection of CCR6⁺CD4⁺ T cell subsets may be critical in maintaining mucosal immune function and preventing disease progression.

We have identified a postentry CCR6-dependent mechanism of inhibition of HIV occurring at an early stage of infection mediated by the induction of the host restriction factor apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G). We observed induction of APOBEC3G expression only in CCR6+ cells but not in cells treated with the G inhibitory (Gi) pathway inhibitor pertussis toxin. CCR6 is highly expressed on peripheral blood CD4+CCR5+ memory T cells and by 2 populations of CD4+ T cells within the gut, α4β7+ and T helper type 17, that have been implicated in cell-to-cell spread of HIV and enhanced restoration of CD4+ T cells within gut-associated lymphoid tissue, respectively. This novel CCR6-mediated mechanism of inhibition allows the identification of pathways that induce intrinsic immunity to HIV, which could be useful in devising novel therapeutics that selectively target CCR6+ cells.

Maintenance of Th1 responses and dendritic cell (DC) functions are compromised in HIV-1 infected individuals. To better understand these immune abnormalities, we developed an HIV-1 transgenic (Tg) rat. We report that Tg DCs induce elevated levels of SOCS-1 and secrete decreased IL-12p40 and elevated levels of IL-10 following TLR-4 stimulation by LPS. This leads to further induction of SOCS-1 by IL-10 and decreased IFN-gamma-mediated induction of interferon response factor (IRF)-1 and IL-12Rbeta1 expression in CD4+ T cells and to decreased IL-12-induction of IFN-gamma production by Th1 polarized T cells. We also show that SOCS-1 is elevated in CD4+ T cells from HIV-1 infected progressors, and is correlated with defective induction of IRF-1 following IFN-gamma stimulation, compared with healthy controls and HIV-1 natural viral suppressor (NVS) patients. These results suggest a link between high levels of SOCS-1, defects in innate immunity and adaptive Th1 responses that may be reflected in the loss of Th1 immune competence observed with AIDS patients.

Lymphangiogenesis and concurrent angiogenesis are essential in supporting proliferation and survival of AIDS-related lymphomas, which are often metastatic. In vitro studies suggest a candidate angiogienic and lymphangiogenic factor encoded by HIV: the matrix protein p17. p17 accumulates in lymph nodes of patients even when they are undergoing highly active antiretroviral therapy. p17 has been found to affect immune cells, and recent data showed that a variant p17, called S75X, induces cell growth by triggering MAPK/ERK and PI3K/AKT pathways. We tested the in vivo angiogenic activity of p17 by injecting it in Matrigel plugs in nude mice. Plugs were retrieved 7 days after injection, and assessed macroscopically, and by light and confocal microscopy. Our data revealed that both reference and S75X variant p17 promote angiogenesis and lymphangiogenesis in vivo. Our results suggest that the induction of angiogenesis and lymphangiogenesis by HIV-1 p17 may generate a favorable microenvironment that could trigger tumor growth and maintenance. Moreover, the presence of adipocytes infiltration observed at the histological level suggests a possible interplay between angiogenesis, lymphangiogenesis and adipogenesis. These findings offer new opportunities for the development of treatment strategies to combat HIV-related cancers.

Accelerated bone loss leading to osteopenia, osteoporosis, and bone fracture is a major health problem that is increasingly common in human immunodeficiency virus (HIV) infected patients. The underlying pathogenesis is unclear but occurs in both treatment naïve and individuals receiving antiretroviral therapies. We developed an HIV-1 transgenic rat that exhibits many key features of HIV disease including HIV-1 induced changes in bone mineral density (BMD). A key determinant in the rate of bone loss is the differentiation of osteoclasts, the cells responsible for bone resorption. We found HIV-1 transgenic osteoclast precursors (OCP) express higher levels of suppressor of cytokine signaling-1 (SOCS-1) and TNF receptor associated factor 6 (TRAF6) and are resistant to interferon-gamma (IFN-γ) mediated suppression of osteoclast differentiation. Our data suggest that dysregulated SOCS-1 expression by HIV-1 transgenic OCP promotes osteoclastogenesis leading to the accelerated bone loss observed in this animal model. We propose that elevated SOCS-1 expression in OCP antagonizes the inhibitory effects of IFN-γ and enhances receptor activator of NF-kB ligand (RANKL) signaling which drives osteoclast differentiation and activation. Understanding the molecular mechanisms of HIV-associated BMD changes has the potential to detect and treat bone metabolism disturbances early and improve the quality of life in patients.

Background Human Immunodeficiency Virus Type I (HIV-1) infection is associated with a high incidence of B-cell lymphomas. The role of HIV in these lymphomas is unclear and currently there are no valid in vivo models for better understanding HIV-related lymphomagenesis. Transgenic (Tg) 26 mice have a 7.4-kb pNL4-3 HIV-1 provirus lacking a 3.1-kb sequence encompassing parts of the gag-pol region. Approximately 15% of these HIV Tg mice spontaneously develop lymphoma with hallmark pre-diagnostic markers including skin lesions, diffuse lymphadenopathy and an increase in pro-inflammatory serum cytokines. Here we describe the phenotypic and molecular characteristics of the B cell leukemia/lymphoma in the Tg mice. Results The transformed B cell population consists of CD19+pre-BCR+CD127+CD43+CD93+ precursor B cells. The tumor cells are clonal and characterized by an increased expression of several cellular oncogenes. Expression of B cell-stimulatory cytokines IL-1β, IL-6, IL-10, IL-12p40, IL-13 and TNFα and HIV proteins p17, gp120 and nef were elevated in the Tg mice with lymphoma. Conclusions Increased expression of HIV proteins and the B-cell stimulatory factors is consistent with the interpretation that one or more of these factors play a role in lymphoma development. The lymphomas share many similarities with those occurring in HIV/AIDS+ patients and may provide a valuable model for understanding AIDS-related lymphomagenesis and elucidating the role played by HIV-1.

s-defensins are antimicrobial peptides secreted by epithelial cells that can bind to cellular receptors. CCR2 and CCR6 are the two cellular receptors known to bind human s-defensin (hBD) 2 and -3. Both of these receptors are of crucial relevance in HIV infection. CCR6 is expressed, often in concert with CCR5, on cells that are highly susceptible to HIV infection: memory T cells, Th17 cells, α4s7+ cells, and defects in CD4+CCR6+ cells have been associated with faster AIDS progression. CCR2 is expressed on monocytes and macrophages, cells that are reservoirs of HIV infection and that are known to mediate central nervous system damage. Our studies show that hBD2, hBD3, and CCR6 ligand MIP-3α/CCL20 inhibit HIV infection via CCR6 by increasing expression of the antiviral protein APOBEC3G. This increase is due to a transcriptional mechanism mediated by intracellular signaling. hBD2 also inhibits HIV replication in macrophages that express CCR2. Our findings suggest novel therapeutic and preventive approaches that exploit CCR6 and CCR2-mediated intracellular signaling to inhibit HIV infection in highly susceptible cells.

T-cell-derived soluble factors that inhibit both X4 and R5 HIV are recognized as important in controlling HIV. Whereas three β chemokines, regulated-on-activation normal T-cell expressed and secreted (RANTES), macrophage inflammatory protein (MIP)-1α, and MIP-1β, account for the suppression of R5 HIV by blockade of HIV entry, the major components responsible for the inhibition of X4 HIV strains have not been identified previously. We identify these factors primarily as a mixture of three β chemokines [macrophage-derived chemokine (MDC), thymus and activation-regulated chemokine (TARC), and I-309] and two RNases (angiogenin and RNase 4) of lesser potency and show that in a clade B population, some correlate with clinical status and are produced by both CD4 + and CD8 + T cells (chemokines, angiogenin) or only by CD8 + T cells (RNase 4). The antiviral mechanisms of these HIV X4-suppressive factors differ from those of the previously described HIV R5-suppressive β chemokines.

Circulating plasmacytoid dendritic cells (pDC) decline during HIV-1 infection, but at the same time they express markedly higher levels of interferon alpha (IFNalpha), which is associated with HIV-1 disease progression. Here we show an accumulation of pDC in lymph nodes (LN) of treatment-naïve HIV-1 patients. This phenomenon was associated with elevated expression of the LN homing marker, CCR7, on pDC in peripheral blood of HIV-1 patients, which conferred increased migratory capacity in response to CCR7 ligands in ex vivo functional assays. LN-homed pDC of HIV-1 patients presented higher CD40 and lower BDCA2 levels, but unchanged CD83 and CD86 expression. In addition, these cells expressed markedly higher amounts of IFNalpha compared to uninfected individuals, and were undergoing faster rates of cell death. These results demonstrate for the first time that in asymptomatic, untreated HIV-1 patients circulating pDC up-regulate CCR7 expression, accumulate in lymph nodes, and express high amounts of IFNalpha before undergoing cell death. Since IFNalpha inhibits cell proliferation and modulates immune responses, chronically high levels of this cytokine in LN of HIV-1 patients may impair differentiation and immune function of bystander CD4(+) T cells, thus playing into the mechanisms of AIDS immunopathogenesis.

Recently, we and others have characterized the HIV-suppressive activity of human β-defensins (hBD) 1–3. Our mechanistic studies indicate that hBD2 inhibits HIV through two distinct mechanisms. The first mechanism results in lower HIV infectivity. The second mechanism is intracellular, since it is observed even delaying treatment up to 2 hours after infection, which is not consistent with a mode of inhibition based on entry-fusion events. We hypothesized that this second antiviral mechanism is due to changes in the intracellular environment, possibly mediated by a cellular receptor. Treatment of cells in infectivity assays with an antibody specific for CCR6, a chemokine receptor that also functions as a receptor for hBD2, abrogated HIV inhibition by this defensin. Further, treatment of HIV-1 infectivity assays with MIP-3α, the cognate ligand for CCR6, resulted in inhibition of infection. Finally, single-cycle HIV infection is inhibited in cells that express CCR6 following transfection with an expression construct, but not in their CCR6low counterpart. Experiments performed using HIV pseudotyped with AMLV envelope showed that inhibition by hBD2 of HIV replication is sensitive to treatment with the Gi protein inhibitor pertussis toxin.CCR6 is an important receptor in the context of mucosal immunity, as it is expressed in CD4+CD45+CCR5+ lymphocytes, which are highly susceptible to HIV infection, and on dendritic cells, which are thought to play a crucial role in early events in HIV transmission. Therefore, an HIV suppressive mechanism targeting CCR6 is likely to play an important role in mucosal immunity to HIV.