Interferon-alpha generation and immune reconstitution during antiretroviral therapy for human immunodeficiency virus infection

MiR-155 Negatively Regulates Anti-Viral Innate Responses among HIV-Infected Progressors

HIV infection impairs host immunity, leading to progressive disease. An anti-retroviral treatment efficiently controls viremia but cannot completely restore the immune dysfunction in HIV-infected individuals. Both host and viral factors determine the rate of disease progression. Among the host factors, innate immunity plays a critical role; however, the mechanism(s) associated with dysfunctional innate responses are poorly understood among HIV disease progressors, which was investigated here. The gene expression profiles of TLRs and innate cytokines in HIV-infected (LTNPs and progressors) and HIV-uninfected individuals were examined. Since the progressors showed a dysregulated TLR-mediated innate response, we investigated the role of TLR agonists in restoring the innate functions of the progressors. The stimulation of PBMCs with TLR3 agonist-poly:(I:C), TLR7 agonist-GS-9620 and TLR9 agonist-ODN 2216 resulted in an increased expression of IFN-α, IFN-β and IL-6. Interestingly, the expression of IFITM3, BST-2, IFITM-3, IFI-16 was also increased upon stimulation with TLR3 and TLR7 agonists, respectively. To further understand the molecular mechanism involved, the role of miR-155 was explored. Increased miR-155 expression was noted among the progressors. MiR-155 inhibition upregulated the expression of TLR3, NF-κB, IRF-3, TNF-α and the APOBEC-3G, IFITM-3, IFI-16 and BST-2 genes in the PBMCs of the progressors. To conclude, miR-155 negatively regulates TLR-mediated cytokines as wel l as the expression of host restriction factors, which play an important role in mounting anti-HIV responses; hence, targeting miR-155 might be helpful in devising strategic approaches towards alleviating HIV disease progression.

Detection of Cytokines and Collectins in Bronchoalveolar Fluid Samples of Patients Infected with Histoplasma capsulatum and Pneumocystis jirovecii

Histoplasmosis and pneumocystosis co-infections have been reported mainly in immunocompromised humans and in wild animals. The immunological response to each fungal infection has been described primarily using animal models; however, the host response to concomitant infection is unknown. The present work aimed to evaluate the pulmonary immunological response of patients with pneumonia caused either by Histoplasma capsulatum, Pneumocystis jirovecii, or their co-infection. We analyzed the pulmonary collectin and cytokine patterns of 131 bronchoalveolar lavage samples, which included HIV and non-HIV patients infected with H. capsulatum, P. jirovecii, or both fungi, as well as healthy volunteers and HIV patients without the studied fungal infections. Our results showed an increased production of the surfactant protein-A (SP-A) in non-HIV patients with H. capsulatum infection, contrasting with HIV patients (p < 0.05). Significant differences in median values of SP-A, IL-1β, TNF-α, IFN-γ, IL-18, IL-17A, IL-33, IL-13, and CXCL8 were found among all the groups studied, suggesting that these cytokines play a role in the local inflammatory processes of histoplasmosis and pneumocystosis. Interestingly, non-HIV patients with co-infection and pneumocystosis alone showed lower levels of SP-A, IL-1β, TNF-α, IFN-γ, IL-18, IL-17A, and IL-23 than histoplasmosis patients, suggesting an immunomodulatory ability of P. jirovecii over H. capsulatum response.

Type I Interferon Induction and Exhaustion during Viral Infection: Plasmacytoid Dendritic Cells and Emerging COVID-19 Findings

Type I Interferons (IFN-I) are a family of potent antiviral cytokines that act through the direct restriction of viral replication and by enhancing antiviral immunity. However, these powerful cytokines are a caged lion, as excessive and sustained IFN-I production can drive immunopathology during infection, and aberrant IFN-I production is a feature of several types of autoimmunity. As specialized producers of IFN-I plasmacytoid (p), dendritic cells (DCs) can secrete superb quantities and a wide breadth of IFN-I isoforms immediately after infection or stimulation, and are the focus of this review. Notably, a few days after viral infection pDCs tune down their capacity for IFN-I production, producing less cytokines in response to both the ongoing infection and unrelated secondary stimulations. This process, hereby referred to as "pDC exhaustion", favors viral persistence and associates with reduced innate responses and increased susceptibility to secondary opportunistic infections. On the other hand, pDC exhaustion may be a compromise to avoid IFN-I driven immunopathology. In this review we reflect on the mechanisms that initially induce IFN-I and subsequently silence their production by pDCs during a viral infection. While these processes have been long studied across numerous viral infection models, the 2019 coronavirus disease (COVID-19) pandemic has brought their discussion back to the fore, and so we also discuss emerging results related to pDC-IFN-I production in the context of COVID-19.

Tissue-specific transcriptional profiling of plasmacytoid dendritic cells reveals a hyperactivated state in chronic SIV infection

HIV associated immune activation (IA) is associated with increased morbidity in people living with HIV (PLWH) on antiretroviral therapy, and remains a barrier for strategies aimed at reducing the HIV reservoir. The underlying mechanisms of IA have not been definitively elucidated, however, persistent production of Type I IFNs and expression of ISGs is considered to be one of the primary factors. Plasmacytoid DCs (pDCs) are a major producer of Type I IFN during viral infections, and are highly immunomodulatory in acute HIV and SIV infection, however their role in chronic HIV/SIV infection has not been firmly established. Here, we performed a detailed transcriptomic characterization of pDCs in chronic SIV infection in rhesus macaques, and in sooty mangabeys, a natural host non-human primate (NHP) species that undergoes non-pathogenic SIV infection. We also investigated the immunostimulatory capacity of lymph node homing pDCs in chronic SIV infection by contrasting gene expression of pDCs isolated from lymph nodes with those from blood. We observed that pDCs in LNs, but not blood, produced high levels of IFNα transcripts, and upregulated gene expression programs consistent with T cell activation and exhaustion. We apply a novel strategy to catalogue uncharacterized surface molecules on pDCs, and identified the lymphoid exhaustion markers TIGIT and LAIR1 as highly expressed in SIV infection. pDCs from SIV-infected sooty mangabeys lacked the activation profile of ISG signatures observed in infected macaques. These data demonstrate that pDCs are a primary producer of Type I IFN in chronic SIV infection. Further, this study demonstrated that pDCs trafficking to LNs persist in a highly activated state well into chronic infection. Collectively, these data identify pDCs as a highly immunomodulatory cell population in chronic SIV infection, and a putative therapeutic target to reduce immune activation.

Infection and cancer suppress pDC derived IFN-I

Plasmacytoid dendritic cells (pDCs) are specialized producers of Type I interferon (IFN-I) that promote anti-viral and anti-tumor immunity. However, chronic infections and cancer inhibit pDC-derived IFN-I. While the mechanisms of this inhibition are multifarious they can be classified broadly into two categories: i) reduction or ablation of pDC IFN-I-production capacity (functional exhaustion) and/or ii) decrease in pDC numbers (altered population dynamics). Recent work has identified many processes that contribute to suppression of pDC-derived IFN-I during chronic infections and cancer, including sustained stimulation through Toll Like Receptors (TLRs), inhibitory microenvironments, inhibitory receptor ligation, and reduced development from bone marrow progenitors and apoptosis. Emerging success leveraging pDCs in treatment of disease through TLR activation illustrates the therapeutic potential of targeting pDCs. Deeper understanding of the systems that limit pDC-derived IFN-I has the potential to improve these emerging therapies as well as help devising new approaches that harness the outstanding IFN-I-production capacity of pDCs.

Innate immune reconstitution with suppression of HIV-1

Progressive HIV-1 infection leads to both profound immune suppression and pathologic inflammation in the majority of infected individuals. While adaptive immune dysfunction, as evidenced by CD4⁺ T cell depletion and exhaustion, has been extensively studied, less is known about the functional capacity of innate immune cell populations in the context of HIV-1 infection. Given the broad susceptibility to opportunistic infections and the dysregulated inflammation observed in progressive disease, we hypothesized that there would be significant changes in the innate cellular responses. Using a cohort of patients with multiple samplings before and after antiretroviral therapy (ART) initiation, we demonstrated increased responses to innate immune stimuli following viral suppression, as measured by the production of inflammatory cytokines. Plasma viral load itself had the strongest association with this change in innate functional capacity. We further identified epigenetic modifications in the TNFA promoter locus in monocytes that are associated with viremia, suggesting a molecular mechanism for the observed changes in innate immune function following initiation of ART. These data indicate that suppression of HIV-1 viremia is associated with changes in innate cellular function that may in part determine the restoration of protective immune responses.

The relation of plasmacytoid dendritic cells (pDCs) and regulatory T-cells (Tregs) with HPV persistence in HIV-infected and HIV-uninfected women

Other than CD4+ count, the immunologic factors that underlie the relationship of HIV/AIDS with persistent oncogenic HPV (oncHPV) and cervical cancer are not well understood. Plasmacytoid dendritic cells (pDCs) and regulatory T-cells (Tregs) are of particular interest. pDCs have both effector and antigen presenting activity and, in HIV-positive patients, low pDC levels are associated with opportunistic infections. Tregs downregulate immune responses, and are present at high levels in HIV-positives. The current pilot study shows for the first time that low pDC and high Treg levels may be significantly associated with oncHPV persistence in both HIV-positive and HIV-negative women. Larger studies are now warranted.

Modulation of inflammasome-mediated pulmonary immune activation by type I IFNs protects bone marrow homeostasis during systemic responses to Pneumocystis lung infection

Although acquired bone marrow failure (BMF) is considered a T cell-mediated autoimmune disease, possible innate immune defects as a cause for systemic immune deviations in response to otherwise innocuous infections have not been extensively explored. In this regard, we recently demonstrated an important role of type I IFNs in protecting hematopoiesis during systemic stress responses to the opportunistic fungal pathogen Pneumocystis in lymphocyte-deficient mice. Mice deficient in both lymphocytes and type I IFN receptor (IFrag(-/-) mice) develop rapidly progressing BMF due to accelerated bone marrow (BM) cell apoptosis associated with innate immune deviations in the BM in response to Pneumocystis lung infection. However, the communication pathway between lung and BM eliciting the induction of BMF in response to this strictly pulmonary infection has been unclear. In this study, we report that absence of an intact type I IFN system during Pneumocystis lung infection not only causes BMF in lymphocyte-deficient mice but also transient BM stress in lymphocyte-competent mice. This is associated with an exuberant systemic IFN-γ response. IFN-γ neutralization prevented Pneumocystis lung infection-induced BM depression in type I IFN receptor-deficient mice and prolonged neutrophil survival time in BM from IFrag(-/-) mice. IL-1β and upstream regulators of IFN-γ, IL-12, and IL-18 were also upregulated in lung and serum of IFrag(-/-) mice. In conjunction, there was exuberant inflammasome-mediated caspase-1 activation in pulmonary innate immune cells required for processing of IL-18 and IL-1β. Thus, absence of type I IFN signaling during Pneumocystis lung infection may result in deregulation of inflammasome-mediated pulmonary immune activation, causing systemic immune deviations triggering BMF in this model.

Plasmacytoid dendritic cell number and responses to Toll-like receptor 7 and 9 agonists vary in HIV Type 1-infected individuals in relation to clinical state

In HIV-1 infection, plasmacytoid dendritic cell (PDC) numbers and function are decreased. No detailed comparisons of PDC responses to various stimuli in HIV-1-infected patients are available. Using for the first time purified PDCs, we compared PDC responses [interferon (IFN)-α production/cell] to various stimuli in a large number (n=48) of HIV-1-infected patients and healthy volunteers (n=19). Toll-like receptor (TLR)7- and TLR9-induced expression of PDC surface activation and maturation markers was also compared in the two populations. We have confirmed that PDC number coincides with CD4(+) T cell counts and clinical state. Notably, we have shown that a direct association of PDC function in terms of IFN-α production/cell exists with PDC numbers and CD4(+) cell counts when PDCs are exposed to a TLR9 ligand and HIV-infected cells, but not with a TLR7 ligand. Moreover, in the HIV-infected subjects but not the healthy controls, the magnitude of IFN-α release per PDC in response to the TLR7 ligand is significantly (p<0.01) lower than that to the TLR9 ligand. However, in both study populations, the TLR7 stimulation in comparison to TLR9 stimulation induced higher expression of PDC surface activation and maturation markers and significantly (p<0.05) decreased the expression of BDCA-2, a negative regulator of interferon. Furthermore, the cross-ligation of BDCA-2 significantly (p<0.05) inhibited TLR9- but not TLR7-induced IFN-α production by PDCs from both clinical groups. These findings suggest that differences exist in TLR7- and TLR9-induced IFN-α production by PDCs in HIV-infected individuals that are not directly related to BDCA-2 down-modulation.

Virus-encoded TLR ligands reveal divergent functional responses of mononuclear phagocytes in pathogenic simian immunodeficiency virus infection

The role of mononuclear phagocytes in the pathogenesis or control of HIV infection is unclear. In this study, we monitored the dynamics and function of dendritic cells (DC) and monocytes/macrophages in rhesus macaques acutely infected with pathogenic SIVmac251 with and without antiretroviral therapy (ART). SIV infection was associated with monocyte mobilization and recruitment of plasmacytoid DC (pDC) and macrophages to lymph nodes, which did not occur with ART treatment. SIVmac251 single-stranded RNA encoded several uridine-rich sequences that were potent TLR7/8 ligands in mononuclear phagocytes of naive animals, stimulating myeloid DC (mDC) and monocytes to produce TNF-α and pDC and macrophages to produce both TNF-α and IFN-α. Following SIV infection, pDC and monocytes/macrophages rapidly became hyporesponsive to stimulation with SIV-encoded TLR ligands and influenza virus, a condition that was reversed by ART. The loss of pDC and macrophage function was associated with a profound but transient block in the capacity of lymph node cells to secrete IFN-α upon stimulation. In contrast to pDC and monocytes/macrophages, mDC increased TNF-α production in response to stimulation following acute infection. Moreover, SIV-infected rhesus macaques with stable infection had increased mDC responsiveness to SIV-encoded TLR ligands and influenza virus at set point, whereas animals that progressed rapidly to AIDS had reduced mDC responsiveness. These findings indicate that SIV encodes immunostimulatory TLR ligands and that pDC, mDC, and monocytes/macrophages respond to these ligands differently as a function of SIV infection. The data also suggest that increased responsiveness of mDC to stimulation following SIV infection may be beneficial to the host.

Downregulation of TLR7/9 leads to deficient production of IFN-α from plasmacytoid dendritic cells in chronic hepatitis B

OBJECTIVE

To investigate whether Toll-like receptor (TLR) 7 and TLR9-mediated interferon α (IFN-α) production in plasmacytoid dendritic cells (pDCs) is compromised in patients with chronic hepatitis B virus (HBV) infection.

MATERIALS AND METHODS

Peripheral blood mononuclear cells (PBMCs) were prepared from 32 chronic HBV patients and 13 healthy volunteers, and treated with loxoribine or cytidine phosphate guanosine (CpG) oligodeoxynucleotides (ODN). Interferon α in the supernatant was measured by sandwich ELISA. PDC frequency and the expression levels of TLR7 and TLR9 in pDCs were quantified by flow cytometry. The serum viral load of HBV was quantified using a highly sensitive real-time PCR kit.

RESULTS

Compared to cells from healthy control group, PBMCs and pDCs from the HBV group showed significantly decreased production of IFN-α in response to ligand for TLR7 (loxoribine) and TLR9 (CpG ODN, P < 0.05). Mechanistically, the number of pDCs in peripheral blood, and the expression of pDC-associated TLR7 and TLR9 were significantly lower in HBV group than in the healthy control group (P < 0.05). In addition, the number of pDCs and the expression of TLR9 on pDCs were correlated inversely with the serum load of HBV.

CONCLUSION

Impaired IFN-α production from pDC may contribute to the immunopathogenesis of chronic HBV infection, which may be the result of a reduced amount of pDCs as well as decreased expression of TLR7 and TLR9 on pDCs.

Type 1 interferons suppress accelerated osteoclastogenesis and prevent loss of bone mass during systemic inflammatory responses to Pneumocystis lung infection

HIV infection causes loss of CD4(+) T cells and type 1 interferon (IFN)-producing and IFN-responsive dendritic cells, resulting in immunodeficiencies and susceptibility to opportunistic infections, such as Pneumocystis. Osteoporosis and bone marrow failure are additional unexplained complications in HIV-positive patients and patients with AIDS, respectively. We recently demonstrated that mice that lack lymphocytes and IFN a/b receptor (IFrag(-/-)) develop bone marrow failure after Pneumocystis lung infection, whereas lymphocyte-deficient, IFN α/β receptor-competent mice (RAG(-/-)) had normal hematopoiesis. Interestingly, infected IFrag(-/-) mice also exhibited bone fragility, suggesting loss of bone mass. We quantified bone changes and evaluated the potential connection between progressing bone fragility and bone marrow failure after Pneumocystis lung infection in IFrag(-/-) mice. We found that Pneumocystis infection accelerated osteoclastogenesis as bone marrow failure progressed. This finding was consistent with induction of osteoclastogenic factors, including receptor-activated nuclear factor-κB ligand and the proapoptotic factor tumor necrosis factor-related apoptosis-inducing ligand, in conjunction with their shared decoy receptor osteoprotegerin, in the bone marrow of infected IFrag(-/-) mice. Deregulation of this axis has also been observed in HIV-positive individuals. Biphosphonate treatment of IFrag(-/-) mice prevented bone loss and protected loss of hematopoietic precursor cells that maintained activity in vitro but did not prevent loss of mature neutrophils. Together, these data show that bone loss and bone marrow failure are partially linked, which suggests that the deregulation of the receptor-activated nuclear factor-κB ligand/osteoprotegerin/tumor necrosis factor-related apoptosis-inducing ligand axis may connect the two phenotypes in our model.

Chronic immune activation in HIV-1 infection contributes to reduced interferon alpha production via enhanced CD40:CD40 ligand interaction

Although a signature of increased interferon (IFN-)alpha production is observed in HIV-1 infection, the response of circulating plasmacytoid dendritic cells (PDC) to Toll-like receptor ligand stimulation is substantially impaired. This functional PDC deficit, which we specifically observed in HIV-1 infected individuals with less than 500 CD4+ T cells/µl, is not well understood. We provide evidence that the peripheral IFN-alpha production in HIV-1 infection is actively suppressed by the enhanced interaction of CD40 ligand (CD40L), a member of the tumor necrosis factor family, and its receptor CD40, which are both upregulated upon immune activation. Plasma levels of soluble CD40L were significantly higher in untreated HIV-1 infected individuals (n = 52) than in subjects on long-term antiretroviral therapy (n = 62, p<0.03) and in uninfected control donors (n = 16, p<0.001). Concomitantly, cell-associated CD40L and the expression of the receptor CD40 on the PDC were significantly upregulated in HIV-1 infection (p<0.05). Soluble and cell-associated CD40L inhibited the PDC-derived IFN-alpha production by CpG oligodeoxynucleotides dose-dependently. This suppressive effect was observed at much lower, physiological CD40L concentrations in peripheral blood mononuclear cells (PBMC) of HIV-1 infected individuals compared to controls (p<0.05). The CpG-induced IFN-alpha production in PBMC of HIV-1 infected donors was directly correlated with PDC and CD4+ T cell counts, and inversely correlated with the viral loads (p<0.001). In HIV-1 infected donors with less than 500 CD4+ T cells/µl, the CpG-induced IFN-alpha production was significantly correlated with the percentage of CD40-expressing PDC and the level of CD40 expression on these cells (p<0.05), whereas CD40L plasma levels played a minor role. In addition, low-dose CD40L contributed to the enhanced production of interleukin 6 and 8 in PBMC of HIV-1 infected donors compared to controls. Our data support the conclusion that the chronic immune activation in HIV-1 infection impairs peripheral PDC innate immune responses at least in part via enhanced CD40:CD40L interactions.

Plasmacytoid dendritic cells reduce HIV production in elite controllers

HIV elite controllers (EC) are a rare group of HIV-infected patients who are able to maintain undetectable viral loads during a long period of time in the absence of antiretroviral treatment. Adaptive immunity and host genetic factors, although implicated, do not entirely explain this phenomenon. On the other hand, plasmacytoid dendritic cells (pDCs) are the principal type I interferon (IFN) producers in response to viral infection, and it is unknown whether pDCs are involved in the control of HIV infection in EC. In our study, we analyzed peripheral pDC levels and IFN-α production by peripheral blood mononuclear cells (PBMCs) in EC compared to other groups of HIV-infected patients, the ability of pDCs to reduce HIV production in vitro, and the mechanisms potentially involved. We showed preserved pDC counts and IFN-α production in EC. We also observed a higher capacity of pDCs from EC to reduce HIV production and to induce T cell apoptosis, whereas pDCs from viremic patients barely responded without previous Toll-like receptor 9 (TLR-9) stimulus. The preserved functionality of pDCs from EC to reduce viral production may be one of the mechanisms involved in the control of HIV viremia in these subjects. These results demonstrate the importance of innate immunity in HIV pathogenesis, and an understanding of pDC mechanisms would be helpful for the design of new therapies.

Blocking type I interferon production: a new therapeutic option to reduce the HIV-1-induced immune activation

Highly active antiretroviral therapy has dramatically improved the morbidity and mortality of HIV-1-infected individuals. A total of 25 licensed drugs provide the basis for an optimized virus-suppressive treatment of nearly each subject. The promises of immune reconstitution and normal life expectancy, however, fall short for a number of patients, either through inadequate recovery of CD4+ T-cell counts or the occurrence of non-AIDS defining malignancies. In this respect, the prevalence of Epstein-Barr virus-associated Hodgkin lymphoma and human papillomavirus-related anal neoplasia is rising in aging HIV-1-infected individuals despite antiretroviral therapy. An important cause appears to be the HIV-1-induced chronic immune activation, propagated by inappropriate release of proinflammatory cytokines and type I interferons. This immune dysregulation can be reduced in vitro by inhibitors blocking the endosomal acidification. Recent data suggest that this concept is also of relevance in vivo, which opens the door for adjuvant immunomodulatory therapies in HIV-1 infection.

Upregulation of BST-2/Tetherin by HIV infection in vivo

The interferon-inducible antiviral factor BST-2 prevents several enveloped viruses, including HIV, from escaping infected cells. The HIV protein Vpu antagonizes this host defense. Little is known about the expression of BST-2 during HIV infection in vivo and whether it can be modulated to the host's advantage. We studied the expression of BST-2 on blood cells from HIV-infected patients during the acute and chronic phases of disease as well as after antiretroviral treatment (ART). The expression of BST-2 was increased on mononuclear leukocytes, including CD4-positive T lymphocytes from HIV-positive patients, compared to that on cells of uninfected controls. The expression of BST-2 was highest during acute infection and decreased to levels similar to those of uninfected individuals after ART. Treatment of primary blood mononuclear cells in vitro with alpha interferon or with Toll-like receptor (TLR) agonists increased the expression of BST-2 to levels similar to those found during infection in vivo. The interferon-induced levels were sufficient to overcome the Vpu protein in vitro, reducing the release of wild-type HIV. These data show that BST-2 is upregulated during HIV infection, consistent with its role as an interferon-stimulated gene. The data further suggest that this upregulation is sufficient to saturate the activity of Vpu and inhibit wild-type HIV.

Virus-host interactions in HIV pathogenesis: directions for therapy

The challenge of controlling HIV infection involves an understanding of the heterogeneity of the virus, its wide cellular host range, its primary routes of transmission, and the immunologic and intrinsic cellular factors that can prevent its transmission and replication. Identification of HIV-infected individuals who have survived more than 10 years without signs of the infection and without therapy encourages studies examining the natural mechanisms for resistance to infection and disease. Within the immune system, emphasis should be given to the innate or natural response that appears within minutes of the infection and offers the optimal time for controlling HIV. All these parameters in HIV pathogenesis underline the information needed to develop optimal anti-HIV therapies and an effective AIDS vaccine.

Efficient infection, activation, and impairment of pDCs in the BM and peripheral lymphoid organs during early HIV-1 infection in humanized rag2⁻/⁻γ C⁻/⁻ mice in vivo

Although plasmacytoid dendritic cells (pDCs) are involved in HIV-1 pathogenesis, the precise mechanism of interaction between pDCs and HIV-1 in vivo is not clear. The conflicting reports in HIV-1-infected patients highlight the importance of studying the interaction between HIV-1 and pDCs in relevant in vivo models. The rag2/γC double knockout (DKO) mouse supports reconstitution of a functional human immune system in central and peripheral lymphoid organs. We report here that functional pDCs were developed in the BM and peripheral lymphoid organs in humanized DKO (DKO-hu) mice. We show that pDCs from both BM and spleen were activated and productively infected during early HIV infection. The activation level of pDCs correlated with that of CD4⁺ T-cell activation and apoptosis. Although CD4⁺ T cells were preferentially depleted, pDCs were maintained but functionally impaired in the BM and spleen of HIV-infected DKO-hu mice. We conclude that HIV-1 can efficiently infect, activate, and impair pDCs in the BM and spleen, in correlation with CD4⁺ T-cell depletion. The humanized mouse will serve as a relevant model to investigate the development and function of pDCs and their role during HIV-1 pathogenesis in vivo.

Loss of NK stimulatory capacity by plasmacytoid and monocyte-derived DC but not myeloid DC in HIV-1 infected patients

Dendritic cells (DC) are potent inducers of natural killer (NK) cells. There are two distinct populations in blood, myeloid (mDC) and plasmacytoid (pDC) but they can also be generated In vitro from monocytes (mdDC). Although it is established that blood DC are lost in HIV-1 infection, the full impact of HIV-1 infection on DC-NK cell interactions remains elusive. We thus investigated the ability of pDC, mDC, and mdDC from viremic and anti-retroviral therapy-treated aviremic HIV-1+ patients to stimulate various NK cell functions. Stimulated pDC and mdDC from HIV-1+ patients showed reduced secretion of IFN-α and IL-12p70 respectively and their capacity to stimulate expression of CD25 and CD69, and IFN-γ secretion in NK cells was also reduced. pDC activation of NK cell degranulation in response to a tumour cell line was severely reduced in HIV-1+ patients but the ability of mDC to activate NK cells was not affected by HIV-1 infection, with the exception of HLA-DR induction. No differences were observed between viremic and aviremic patients indicating that anti-retroviral therapy had minimal effect on restoration on pDC and mdDC-mediated activation of NK cells. Results from this study provide further insight into HIV-1 mediated suppression of innate immune functions.

Spatiotemporal trafficking of HIV in human plasmacytoid dendritic cells defines a persistently IFN-α-producing and partially matured phenotype

Plasmacytoid DCs (pDCs) are innate immune cells that are specialized to produce IFN-α and to activate adaptive immune responses. Although IFN-α inhibits HIV-1 replication in vitro, the production of IFN-α by HIV-activated pDCs in vivo may contribute more to HIV pathogenesis than to protection. We have now shown that HIV-stimulated human pDCs allow for persistent IFN-α production upon repeated stimulation, express low levels of maturation molecules, and stimulate weak T cell responses. Persistent IFN-α production by HIV-stimulated pDCs correlated with increased levels of IRF7 and was dependent upon the autocrine IFN-α/β receptor feedback loop. Because it has been shown that early endosomal trafficking of TLR9 agonists causes strong activation of the IFN-α pathway but weak activation of the NF-κB pathway, we sought to investigate whether early endosomal trafficking of HIV, a TLR7 agonist, leads to the IFN-α-producing phenotype we observed. We demonstrated that HIV preferentially traffics to the early endosome in human pDCs and therefore skews pDCs toward a partially matured, persistently IFN-α-secreting phenotype.

Chinese human immunodeficiency virus-1 patients with different routes of transmission exhibit altered expression levels of blood dendritic cell subpopulations

Dendritic cells (DCs) play a pivotal role in the pathogenesis of human immunodeficiency virus-1 (HIV-1). Reduced numbers of blood DCs have been observed in individuals with chronic HIV-1 infection. In the present study, we analyzed the expression levels of monocytes, myeloid dendritic cell (mDC) precursors, mDCs, and plasmacytoid dendritic cells (pDCs), in HIV-1-infected patients in China who were infected via different routes of transmission, including heterosexual and homosexual sexual contact, and blood transmission through importation of blood or blood products, to further elucidate their role in HIV. Compared with HIV-negative individuals (n = 40), relative levels of CD11c+CD14⁻mDCs, CD11c++CD123(low) mDCs, and CD11c⁻CD123+ pDCs in total peripheral blood mononuclear cells (PBMCs) were significantly lower in all HIV patients (n = 93), and in those with blood transmission (n = 26) and heterosexual transmission (n = 43), while relative levels of CD11c+CD14⁻mDCs were significantly lower in HIV patients infected via homosexual transmission (n = 24). The results of correlation analysis demonstrated a significant negative correlation between CD4+ T-cell counts and the relative levels of CD11c++CD123(low) mDCs in HIV-I patients infected via blood transmission. There was no significant correlation between CD4+ T-cell counts and the expression level of other DC subpopulations in PBMCs from HIV patients. The results of this study suggest that HIV-1 patients with different routes of transmission exhibit altered expression levels of blood DC subpopulations, which contributes to dysregulated immune responses and pathogenesis of HIV-1.

Age-dependent changes in peripheral blood dendritic cell subsets in normal children and children with specific polysaccharide antibody deficiency (SPAD)

Myeloid and plasmacytoid dendritic cells (MDC/PDC) play crucial roles in bridging adaptive and innate immunity by affecting development of both cellular and humoral immunity. The immune system evolves after birth as reflected in dynamic changes in numbers and functions of various immune cells with age. However, age-associated changes in DC subsets in children have not been elucidated despite the fact that such normative data are crucial for evaluating alternations of DC subsets in various pediatric diseases. This study addressed age-associated changes in DC subsets and CD40/86 expression on PDC (markers of maturation/activation) in 50 healthy children in comparison with 25 children with specific polysaccharide antibody deficiency (SPAD). Our results revealed age-dependent decrease of PDC numbers (p < 0.0001), although there was no age-associated changes in CD40/CD86 expression. MDC1/MDC2 numbers did not reveal such linear age-dependent changes and MDC1/PDC ratio reached around 2 as typically seen in young adults after 10 years of age. In contrast, SPAD patients did not reveal such age-associated changes and showed decreased fluorescence intensity of CD86 in PDC cells. These results indicate lineage specific, age-dependent changes in DC subsets in normal children and possible altered development of these cells in SPAD children, emphasizing the importance of age-appropriate controls.

Evidence of dysregulation of dendritic cells in primary HIV infection

Myeloid and plasmacytoid dendritic cells (DCs) are important mediators of both innate and adaptive immunity against pathogens such as HIV. During the course of HIV infection, blood DC numbers fall substantially. In the present study, we sought to determine how early in HIV infection the reduction occurs and whether the remaining DC subsets maintain functional capacity. We find that both myeloid DC and plasmacytoid DC levels decline very early during acute HIV infection. Despite the initial reduction in numbers, those DCs that remain in circulation retain their function and are able to stimulate allogeneic T-cell responses, and up-regulate maturation markers plus produce cytokines/chemokines in response to stimulation with TLR7/8 agonists. Notably, DCs from HIV-infected subjects produced significantly higher levels of cytokines/chemokines in response to stimulation with TLR7/8 agonists than DCs from uninfected controls. Further examination of gene expression profiles indicated in vivo activation, either directly or indirectly, of DCs during HIV infection. Taken together, our data demonstrate that despite the reduction in circulating DC numbers, those that remain in the blood display hyperfunctionality and implicates a possible role for DCs in promoting chronic immune activation.

Type-I IFN signaling suppresses an excessive IFN-gamma response and thus prevents lung damage and chronic inflammation during Pneumocystis (PC) clearance in CD4 T cell-competent mice

Immune-reconstitution after highly active antiretroviral therapy (HAART) is often incomplete, and some HIV-infected individuals fail to regenerate type-I interferon (IFN)-producing pDCs. We recently demonstrated that during Pneumocystis (PC) infection in CD4 T cell-competent mice the absence of type-I IFN signaling results in chronic pulmonary inflammation and fibrosis despite clearance. Because the mechanisms involved are poorly understood, we further characterized the role of type-I IFN signaling in immune responses to PC. We show that type-I IFN signaling around day 7 postinfection is critical to the outcome of inflammation. Microarray analysis of pulmonary CD11c(+) cells revealed that at day 7 post infection, wild-type cells up-regulated type-I IFN-responsive genes as well as SOCS1, which is a critical negative-regulator of type-I IFN and IFN-gamma signaling. This was associated with an eosinophilic lung inflammation, PC clearance, and complete restitution. However, pulmonary CD11c(+) cells from IFNAR(-/-) mice demonstrated increased tumor necrosis factor (TNF)-alpha production and lacked SOCS1-induction at day 7. This was followed by a transient lymphocytic and IFN-gamma response before switching to a chronic eosinophilic inflammation of the lung. Early neutralization of TNF-alpha did not prevent chronic inflammation in IFNAR(-/-) mice, but treatment with an anti-IFN-gamma antibody did. We propose that during PC lung infection type-I IFNs induce SOCS1-associated regulatory mechanisms, which prevent excessive IFN-gamma-mediated responses that cause chronic lung damage. Therefore, partial immune-reconstitution in AIDS, attributable to reduced type-I IFN actions, might disrupt regulatory aspects of inflammation, causing unexplained chronic pulmonary complications as seen in some patients during HAART.

Current understanding of Pneumocystis immunology

Pneumocystis jirovecii is the opportunistic fungal organism that causes Pneumocystis pneumonia (PCP) in humans. Similar to other opportunistic pathogens, Pneumocystis causes disease in individuals who are immunocompromised, particularly those infected with HIV. PCP remains the most common opportunistic infection in patients with AIDS. Incidence has decreased greatly with the advent of HAART. However, an increase in the non-HIV immunocompromised population, noncompliance with current treatments, emergence of drug-resistant strains and rise in HIV(+) cases in developing countries makes Pneumocystis a pathogen of continued interest and a public health threat. A great deal of research interest has addressed therapeutic interventions to boost waning immunity in the host to prevent or treat PCP. This article focuses on research conducted during the previous 5 years regarding the host immune response to Pneumocystis, including innate, cell-mediated and humoral immunity, and associated immunotherapies tested against PCP.

Plasmacytoid dendritic cells in HIV infection: striking a delicate balance

pDC are the most potent IFN-alpha-producing cells in the body and serve as a vital link between innate and adaptive immunity. Deficiencies in pDC function were among the earliest observations of immune dysfunction in HIV-1 infection. Herein, we review the status of pDC in individuals with HIV-1 infection and the potential role of these cells in pathogenesis. We begin by reviewing the basic properties of pDC and then discuss the compromise in circulating pDC numbers and function in early and viremic HIV-1 infection and mechanisms that might account for their depletion in HIV-infected patients. In addition, we review the evidence that chronic production of IFN-alpha, probably through the chronic activation of pDC, is central to the immune activation that is so detrimental in HIV infection. Finally, we discuss the importance of balance in pDC numbers and function and the potential value of using absolute pDC counts and function as a biomarker, along with CD4(+) cell counts and VL in HIV-1-infected patients.

Differential effects of P-class versus other CpG oligodeoxynucleotide classes on the impaired innate immunity of plasmacytoid dendritic cells in HIV type 1 infection

Abstract Human plasmacytoid dendritic cells (PDC) are the major producers of type I interferons (IFN) after stimulation with CpG oligodeoxynucleotides (ODN). HIV-1-infected patients show a deficit in PDC numbers and function with progression of disease. CpG ODN appear to be attractive therapeutics to support the impaired innate immunity in HIV-1 infection. PDC counts, phenotype, and function were analyzed in 23 HIV-infected untreated individuals and 16 controls. Markers for migration (CCR7), activation (CD80), maturation (CD83), and endocytosis (BDCA2) were evaluated at baseline and 20 h after in vitro stimulation with class A, B, C, and P ODN. PDC counts and the expression of BDCA2 on these cells were significantly lower in HIV-1-infected subjects compared to controls (both p < 0.001). After stimulation with CpG ODN, CD80 and CD83 were upregulated to a similar extent in patients and controls, whereas CCR7 was upregulated more efficiently by CpG-P and CpG-C than CpG-A in HIV-1-infected individuals compared to controls. The IFN-alpha induction significantly differed for the CpG ODN classes (A > P > C > B) in patients and controls (p < 0.05). Functional PDC deficits in IFN-alpha and TNF-alpha induction were particularly evident in subjects with less than 500 CD4(+) cells/mul. CpG-P ODNs not only induced remarkable IFN-alpha production in patient PBMCs, but also significantly upregulated the antibacterial and antiviral CXC chemokine IP-10. In conclusion, PDC counts, phenotype, and function are significantly impaired in HIV-1-infected subjects. Optimized P-class ODN may be effective in reversing this innate immune defect, which should be further evaluated in vivo.

Persistent virus infection inhibits type I interferon production by plasmacytoid dendritic cells to facilitate opportunistic infections

Emerging studies indicate an association between virus-induced impairment in type I interferon (IFN-I) production and enhanced susceptibility to opportunistic infections, which represent a major health problem. Here, we provide in vivo evidence that lymphocytic choriomeningitis virus (LCMV) infection of its natural murine host dramatically diminishes the unique capacity of plasmacytoid dendritic cells (pDCs) to secrete high levels of systemic IFN-I. While both acute and persistent LCMV infections suppress pDC IFN-I response, only the persistent virus induces a long-lasting diversion of this innate immune pathway. The consequent reduction in IFN-I production serves to impair natural killer cell responses in LCMV-infected mice challenged subsequently with murine cytomegalovirus (MCMV) as an opportunistic pathogen. This innate defect also compromises the host's ability to counteract early MCMV spread. These findings provide a mechanistic explanation for the occurrence of opportunistic infections following viral insults and have important implications for treating such medical complications.

Decreased interferon-alpha production and impaired regulatory function of plasmacytoid dendritic cells induced by the hepatitis C virus NS 5 protein

pDC are known to produce large amount of IFN-alpha/beta in response to viruses, and act as a major link between the innate and adaptive immune response. This study concentrated on the interaction of human peripheral blood derived pDC with HCV NS3, NS4, and NS5 proteins, and their maturation, cytokine secretion and functional properties. It was shown that HCV NS5 interferes with CD40L induced maturation of pDC as indicated by decreased expression of CD83 and CD86 markers. CpG ODN stimulated HCV NS3 and NS5 treated pDC showed decreased production of IFN-alpha. In the case of NS3, IFN-alpha production was reduced to 126 pg/ml as compared to 245 pg/ml in controls (P < 0.01), and with NS5, IFN-alpha production was reduced to 92 pg/ml as compared to 238 pg/ml in controls (P < 0.05). In the presence of HCV NS5, the T cell stimulatory capacity of pDC was impaired, as indicated by decreased proliferation of T cells, and decreased production by the T cells of IFN-gamma, which were down to 86 pg/ml as compared to 260 pg/ml in controls (P < 0.05). These results suggest that HCV NS5 impairs pDC function and is in agreement with several other in vivo studies indicating decreased numbers of, and dysfunctional pDC, in chronic HCV infected patients.

Decreased type I interferon receptor-soluble isoform in antiretroviral-treated HIV-positive children

We developed a real-time PCR assay to simultaneously measure the mRNA level of type I interferon (IFN) receptor (IFNAR) components in peripheral blood cells of children with chronic immune stimulation due to HIV infection. All patients were undergoing antiretroviral therapy and were divided into two groups on the basis of the induction of MxA mRNA, a marker of type I IFN bioactivity. We found that IFNAR-2 subunit mRNA was higher than that of the IFNAR-1 subunit, that the mRNA for the IFNAR-2.2 functional isoform was more expressed than that for the truncated IFNAR-2.1 isoform, and both were much more represented than that of the IFNAR-2.3 soluble isoform. We also demonstrated that soluble isoform mRNA was significantly diminished in the subgroup of patients with MxA mRNA below the cutoff value (determined as the 99th percentile of MxA measured in healthy controls). These results suggest that downregulation of the soluble receptor isoform, which would not compete with the functional isoform for binding to the target cytokine, would give type I IFN, eventually induced in these patients in the case of viral reactivation, the opportunity to promptly exert its antiviral activity.

CD4 binding affinity determines human immunodeficiency virus type 1-induced alpha interferon production in plasmacytoid dendritic cells

Plasmacytoid dendritic cells (PDC) are major producers of type I interferons (IFN) in response to human immunodeficiency virus type 1 (HIV-1) infection. To better define the underlying mechanisms, we studied the magnitude of alpha IFN (IFN-alpha) induction by recombinant viruses containing changes in the Env protein that impair or disrupt CD4 binding or expressing primary env alleles with differential coreceptor tropism. We found that the CD4 binding affinity but not the viral coreceptor usage is critical for the attachment of autofluorescing HIV-1 to PDC and for subsequent IFN-alpha induction. Our results illustrate the importance of the gp120-CD4 interaction in determining HIV-1-induced immune stimulation via IFN-alpha production.

Human immunodeficiency virus viremia induces plasmacytoid dendritic cell activation in vivo and diminished alpha interferon production in vitro

Human immunodeficiency virus type 1 (HIV-1) infection has been associated with perturbations of plasmacytoid dendritic cells (PDC), including diminished frequencies in the peripheral blood and reduced production of type I interferons (IFNs) in response to in vitro stimulation. However, recent data suggest a paradoxical increase in production of type 1 interferons in vivo in HIV-infected patients compared to uninfected controls. Using a flow cytometric assay to detect IFN-alpha-producing cells within unseparated peripheral blood mononuclear cells, we observed that short-term interruptions of antiretroviral therapy are sufficient to result in significantly reduced IFN-alpha production by PDC in vitro in response to CpG A ligands or inactivated HIV particles. The primary cause of diminished IFN-alpha production was reduced responsiveness of PDC to de novo stimulation, not diminished per cell IFN-alpha production or migration of cells to lymphoid organs. Real-time PCR analysis of purified PDC from patients prior to and during treatment interruptions revealed that active HIV-1 replication is associated with upregulation of type I IFN-stimulated gene expression. Treatment of hepatitis C virus-infected patients with IFN-alpha2b and ribavirin for hepatitis C virus infection resulted in a profound suppression of de novo IFN-alpha production in response to CpG A or inactivated HIV particles, similar to the response observed in HIV-infected patients. Together, these results suggest that diminished production of type I interferons in vitro by PDC from HIV-1-infected patients may not represent diminished interferon production in vivo. Rather, diminished function in vitro is likely a consequence of prior activation via type I interferons or HIV virions in vivo.

Role for plasmacytoid dendritic cells in anti-HIV innate immunity

The role of plasmacytoid dendritic cells (pDC) in anti-HIV immunity is mostly represented by the production of type I IFN in response to HIV infection in vitro and in vivo. This production is decreased in HIV-1 infected patients at the time of primary infection and during chronic disease in association with progression of disease. Circulating pDC counts are decreased concomitantly with type I IFN, and both factors correlate inversely overall with viral loads and positively with CD4+ T-cell counts. These parameters might be used in clinical immunology to monitor treatment and as predictive factors of immune control of HIV-1 replication to help decide whether to interrupt antiretroviral treatment. They may be related to control of HIV replication as well as to pathogenesis of infection, perhaps in setting the balance between immunity or tolerance to the virus. A better understanding of these parameters is required while attempts to use IFN-alpha or ligands of Toll-like receptors found on pDC are being made.

Clinical analysis of dendritic cell subsets: the dendritogram

Dendritic cells (DCs) are crucial in adaptive immunity because they are the only antigen-presenting cells that can present antigens to naive T lymphocytes. Plasmacytoid DCs (pDC) are also the main producers of type I Interferons in response to infection. We have shown that circulating myeloid DC (mDC) and pDC numbers are reduced in chronic as well as primary HIV infection. Data from different laboratories indicate that pDC counts, obtained by flow cytometry and rare event analysis, correlate inversely with the viral load, may be an early marker of recovery after antiretroviral treatment, and may predict better immune control of HIV replication. PDC counts may also be predictive of severe illness in dengue virus infection or of successful treatment against Mycobacterium tuberculosis. DC counts, or the "dendritogram", may therefore become useful in the clinical assessment of different infectious diseases.

An interferon-alpha-induced tethering mechanism inhibits HIV-1 and Ebola virus particle release but is counteracted by the HIV-1 Vpu protein

Type 1 interferon (IFN) inhibits the release of HIV-1 virus particles via poorly defined mechanisms. Here, we show that IFNalpha induces retention of viral particles on the surface of fibroblasts, T cells, or primary lymphocytes infected with HIV-1 lacking the Vpu protein. Retained particles are tethered to cell surfaces, can be endocytosed, appear fully assembled, exhibit mature morphology, and can be detached by protease. Strikingly, expression of the HIV-1 Vpu protein attenuates the ability of human cells to adhere to, and thereby retain, nascent HIV-1 particles upon IFNalpha treatment. Vpu also counteracts the IFNalpha-induced retention of virus-like particles assembled from the Ebola virus matrix protein. Furthermore, levels of IFNalpha that suppress replication of Vpu-defective HIV-1 have little effect on wild-type HIV-1. Thus, we propose that HIV-1 expresses Vpu to counteract an IFNalpha-induced, general host defense that inhibits dissemination of enveloped virions from the surface of infected cells.

Association of cutaneous anergy with human papillomavirus and cervical neoplasia in HIV-seropositive and seronegative women

OBJECTIVE

Cutaneous anergy testing evaluates delayed type hypersensitivity responses and is, in essence, an in-vivo measure of cell-mediated immune function at an epithelial surface. This study assessed the relationship of anergy test results with cervical infection by human papillomavirus (HPV) and cervical neoplasia in HIV-seropositive and seronegative women.

METHODS

HIV-seropositive (n = 1029) and HIV-seronegative (n = 272) women enrolled in a long-term cohort study were followed semi-annually with HPV-DNA testing and cytology. Anergy was defined as unresponsiveness to Candida albicans, tetanus toxoid, and mumps antigen.

RESULTS

Anergy was associated with the prevalent detection of squamous intraepithelial lesions [SIL; adjusted odds ratio 1.70; 95% confidence interval (CI) 1.16-2.48] in multivariable logistic regression models, and with the incident detection of oncogenic HPV (adjusted hazard ratio 1.24; 95% CI 0.99-1.56) in multivariable Cox regression models. These models adjusted for HIV infection, combined CD4 T-cell and HIV-RNA strata (13 separate strata to control optimally for their interactive effects), as well as other variables.

CONCLUSION

Cutaneous anergy testing may measure aspects of local cellular immune function in epithelial tissues that are important for the control of HPV and development of SIL, and that in HIV-seropositive women are not fully accounted for by circulating CD4 T-cell counts and HIV-RNA levels.

Impaired CCR7 expression on plasmacytoid dendritic cells of HIV-infected children and adolescents with immunologic and virologic failure

BACKGROUND

Defects of plasmacytoid (p) and myeloid (m) dendritic cells (DCs) occur in HIV infection. The aim of this study was to evaluate the maturation and function of DCs in children with perinatal HIV infection who were on antiretroviral therapy.

MATERIALS AND METHODS

Twenty HIV-infected children (median age = 12.9 years) classified as immunologic/virologic responders and failures were evaluated in a whole-blood assay with resiquimod (RSQ), a potent agonist to Toll-like receptors 7 and 8, as the DC stimulant.

RESULTS

In comparison to controls, pDC and mDC numbers were decreased in patients, but RSQ stimulation resulted in upregulation of CD83, CD80, and tumor necrosis factor-alpha in both DC subsets and upregulation of interferon (IFN)-alpha in pDCs. Patients with immunologic and virologic failure demonstrated a selective impairment in upregulation of lymph node homing marker CCR7 in pDCs. Plasma virus load was negatively correlated with IFNalpha and CCR7 expression, whereas CD4 percentage correlated only with CCR7 expression in pDCs.

CONCLUSIONS

A novel defect of pDCs, impaired CCR7 upregulation, is described in association with immunologic or virologic failure. This deficiency could impair homing of pDCs to lymph nodes, leading to secondary defects of mDC maturation and poor T-cell activation.

Baseline Viral Load and Immune Activation Determine the Extent of Reconstitution of Innate Immune Effectors in HIV-1-Infected Subjects Undergoing Antiretroviral Treatment

We analyzed dendritic cell (DC) and NK cell compartments in relation to CD4 recovery in 21 HIV-infected subjects followed to <50 copies/ml once starting antiretroviral therapy (ART) and observed for 52 wk of sustained suppression. Although CD4 counts increased in all subjects in response to ART, we observed a restoration of functional plasmacytoid DC (PDC) after 52 wk of sustained suppression under ART (from 1850 cells/ml to 4550 cells/ml) to levels comparable to controls (5120 cells/ml) only in subjects with a low baseline viral load, which also rapidly suppressed to <50 copies/ml upon <or=60 days from ART initiation. Recovery of PDC at week 52 correlates with level of CD95 expression on CD8 T cells and PDC frequency following first ART suppression. NK cytotoxic activity increased rapidly upon viral suppression (VS) and correlated with PDC function at week 52. However, restoration of total NK cells was incomplete even after 52 wk on ART (73 cells/mul vs 122 cells/mul in controls). Direct reconstitution experiments indicate that NK cytotoxic activity against virally infected target cells requires DC/NK cooperation, and can be recovered upon sustained VS and recovery of functional PDC (but not myeloid DC) from ART-suppressed subjects. Our data indicate that viremic HIV-infected subjects may have different levels of reconstitution of DC and NK-mediated function following ART, with subjects with lower initial viremia and the greatest reduction of baseline immune activation at VS achieving the greatest level of innate effector cell reconstitution.

Type I Interferon Signaling and B Cells Maintain Hemopoiesis duringPneumocystisInfection of the Lung

Loss of CD4 T cells is the hallmark of HIV infection. However, type I IFN-producing plasmacytoid dendritic cells may also be lost. This results in susceptibility to an opportunistic infection such as Pneumocystis pneumonia. In addition, regenerative bone marrow failure resulting in pancytopenia is another common problem in advanced stage AIDS. This may be linked to both the failing immune system and recurrent opportunistic infections. We generated lymphocyte-deficient type I IFN receptor-deficient mice (IFrag-/-) to study the effects on Pneumocystis infection of the lung. When IFrag-/- animals were infected with Pneumocystis they died between days 16 and 21 postinfection with minimal pneumonia but severe anemia due to complete bone marrow failure. This included the loss of uncommitted hemopoietic precursor cells. Bone marrow failure was prevented by the reconstitution of IFrag-/- mice with wild-type lymphocytes, especially B cells. T and B cells lacking type I IFN receptor signaling could only partially prevent bone marrow failure in response to Pneumocystis infection. However, the presence of T and B cells lacking type I IFN signaling resulted in compensatory extramedullary hemopoiesis in the liver and spleen. Lymphocyte support of the regenerative capacity of the bone marrow was provided by both type I IFN-dependent and -independent mechanisms that acted synergistically. Our findings point to the requirement of both type I IFNs and lymphocytes in the regenerative capabilities of the hemopoietic system under the pressure of Pneumocystis infection, but not during steady-state hemopoiesis. This may have implications in the management of pancytopenia in AIDS.

HIV-1 immunopathogenesis: how good interferon turns bad

The hallmark of acquired immunodeficiency syndrome (AIDS) is the progressive loss of CD4+ T cells that results from infection with human immunodeficiency virus type-1 (HIV-1). Despite 25 years of AIDS research, questions remain concerning the mechanisms responsible for HIV-induced CD4+ T cell depletion. Here we briefly review the in vitro and in vivo literature concerning the protective role of interferon-alpha (IFN-alpha) in HIV/AIDS. We then develop a laboratory- and clinically supported model of CD4+ T cell apoptosis in which either infectious or noninfectious HIV-1 induces the production of type I interferon by plasmacytoid dendritic cells (pDC). The interferon produced binds to its receptor on primary CD4+ T cells resulting in membrane expression of the TNF-related apoptosis-inducing ligand (TRAIL) death molecule. The binding of infectious or noninfectious HIV-1 to CD4 on these T cells results in expression of the TRAIL death receptor 5 (DR5), leading to the selective death of HIV-exposed CD4+ T cells.

Plasmacytoid dendritic cells--virus experts of innate immunity

Plasmacytoid dendritic cells (pDC) have emerged as a principal subset of dendritic cells in both human and mouse. PDC morphology, surface markers, their migration in vivo and the ability to rapidly produce large amounts of type I interferons (IFN-alpha/beta) in response to toll like receptor (TLR) triggering sets them apart from other dendritic cell subsets. This review highlights the features that make pDC uniquely able to sense and respond to viral infection.

Early and delayed benefits of HIV-1 suppression: timeline of recovery of innate immunity effector cells

OBJECTIVE

The kinetics of recovery for innate immune effectors following antiretroviral therapy are unknown.

DESIGN AND METHODS

Multiple sequential cryopreserved samples (viremic and ART-suppressed) from 66 patients enrolled in the Women's Interagency HIV Study or Multicenter AIDS Cohort Study cohorts (median follow-up, 700 days) were analyzed to determine natural killer, dendritic and T-cell changes by flow cytometry. Functional parameters were also measured in a subset of samples. Changes over time were analyzed by mixed-effect modeling based on a linear spline with a single knot at 270 days.

RESULTS

Following viral suppression, a rapid rise in CD4 and white blood cell counts and a decline in T-cell activation were confirmed. However, natural killer cell subsets increased after 270 days of therapy, with a negative effect by baseline CD4%. CD123+ plasmacytoid but not myeloid dendritic cells showed a trend to increase during the first 270 days with a positive effect of baseline CD4%; plasmacytoid dendritic cell-induced interferon-alpha production significantly increased by end of follow-up.

CONCLUSIONS

The kinetics of natural killer and plasmacytoid dendritic cell recovery are markedly different from those of T-cell subsets, indicative of early and delayed benefits of suppressive regimens.

Local and systemic effects of intranodally injected CpG-C immunostimulatory-oligodeoxyribonucleotides in macaques

Immunostimulatory CpG-C oligodeoxyribonucleotides (ISS-ODNs) represent a promising strategy to enhance vaccine efficacy. We have shown that the CpG-C ISS-ODN C274 stimulates macaque blood dendritic cells (DCs) and B cells and augments SIV-specific IFN-gamma responses in vitro. To further explore the potential of C274 for future vaccine studies, we assessed the in vivo effects of locally administered C274 (in naive and healthy infected macaques). Costimulatory molecules were marginally increased on DCs and B cells within cells isolated from C274-injected lymph nodes (LNs). However, cells from C274-injected LNs exhibited heightened responsiveness to in vitro culture. This was particularly apparent at the level of CD80 (less so CD86) expression by CD123(+) plasmacytoid DCs and was further boosted in the presence of additional C274 in vitro. Notably, cells from C274-injected LNs secreted significantly elevated levels of several cytokines and chemokines upon in vitro culture. This was more pronounced when cells were exposed to additional stimuli in vitro, producing IFN-alpha, IL-3, IL-6, IL-12, TNF-alpha, CCL2, CCL3, CCL5, and CXCL8. Following C274 administration in the absence of additional SIV Ag, endogenous IFN-gamma secretion was elevated in LN cells of infected animals, but SIV-specific responses were unchanged. Endogenous and SIV-specific responses decreased in blood, before the SIV-specific responses rebounded by 2 wk after C274 treatment. Elevated IFN-alpha, CCL2, and CCL5 were also detected in the plasma after C274 injection. Thus, locally administered C274 has local and systemic activities, supporting the potential for CpG-C ISS-ODNs to boost immune function to enhance anti-HIV vaccine immunogenicity.

Innate immune defenses in HIV-1 infection: prospects for a novel immune therapy

HIV-1 infection leads to a severe decrease of CD4(+) T lymphocytes, dysregulation of several leukocyte subpopulations and generalized immune activation, with the subsequent development of opportunistic infections and malignancies. Administration of highly active antiretroviral therapy (HAART) has been successful in reducing HIV-1 plasma viremia; however, the ability of HAART to restore immunocompetence appears incomplete, particularly in patients with chronic and advanced disease. Several components of the innate immune system have direct anti-HIV-1 effects, and studies to analyze the benefits of enhancing the function of the innate response during HIV-1 infection are increasing. Development of any complementary therapeutic approaches to HIV-1 infection, particularly those able to compensate for the limitations of HAART, and enhance the anti-HIV-1 innate immune activity would be of interest. The stimulation of innate immune responses using Toll-like receptor agonists, such as monophosphoryl lipid A and oligodeoxynucleotides with CpG motifs, are currently being investigated and their benefit in HIV-1-infected patients are under evaluation.

Selective defect in plasmacyoid dendritic cell function in a patient with AIDS-associated atypical genital herpes simplex vegetans treated with imiquimod

We report a case of acquired immunodeficiency syndrome (AIDS)-associated, acyclovir-refractory genital herpes infection treated with topical imidazoquinoline therapy. The patient's plasmacytoid dendritic cells made a robust interferon- alpha response following in vitro stimulation with imidazoquinoline but not with herpes simplex virus. We hypothesize that disease resulting from defective herpes simplex virus-stimulated interferon- alpha may be overcome by stimulating intact alternative pathways.

Type I interferon production in HIV-infected patients

Type I IFNs display multiple biological effects. They have a strong antiviral action, not only directly but also indirectly through activation of the immune system. They may also have actions that are deleterious for the host. The cells that produce type I IFN are mostly plasmacytoid dendritic cells (pDC), but this depends on the viral stimulus. The migration and distribution of pDC into lymphoid organs, driven by chemokine interactions with their ligands, determines interaction with different cell types. In HIV infection, IFN production in vitro is impaired during primary infection and later in association with opportunistic infections. Circulating pDC numbers are decreased in parallel. These parameters may be used to help assess the prognosis of the disease and to monitor treatment.

Similar changes in plasmacytoid dendritic cell and CD4 T-cell counts during primary HIV-1 infection and treatment

OBJECTIVES

Reduced dendritic cell (DC) frequencies and functions in individuals with longstanding HIV-1 infection are predictive of opportunistic infections and AIDS. To investigate possible early alterations in DC levels after HIV infection, we prospectively examined plasmacytoid dendritic cell (pDC) and myeloid dendritic cell (mDC) frequencies and plasma IFN-alpha levels in patients undergoing primary HIV-1 infection (PHI).

METHODS

Peripheral blood DC frequencies and absolute counts were determined by flow cytometry. Plasma IFN-alpha levels were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

In comparison to uninfected subjects, pDC, but not mDC, levels were reduced (P < 0.001) in subjects with PHI, especially in those with high viral loads or low CD4 T-cell counts. During 24-48 weeks of observation, untreated subjects experienced slight declines in pDC and CD4 T-cell levels. In contrast, subjects initiating early antiretroviral therapy (ART) exhibited increases (P < 0.001) in pDC and CD4 T-cell counts. No effect of treatment on mDC counts was observed. Circulating plasma IFN-alpha was undetectable by ELISA regardless of the duration of HIV-1 infection.

CONCLUSION

PHI is characterized by a reduction in pDC and CD4 T-cell counts that correlates with the magnitude of virus replication and is not evidenced by the mDC count or plasma IFN-alpha level. Early ART appears to have similar restorative effects on pDC and CD4 T-cell counts.