BACKGROUND:The treatment landscape for type 2 diabetes (T2D) is continually evolving; therefore, ongoing education of health care professionals (HCPs) is essential. There is growing interest in measuring the impact of educational activities, such as through use of the Moore framework; however, data on the benefits of continuing medical education (CME) in the management of T2D remain limited.OBJECTIVE:This study aimed to evaluate HCP satisfaction; measure improvements in knowledge, competence, and performance following short, case-based, multidisciplinary web-based CME activities; and identify the remaining educational gaps.METHODS:Two faculty-led, CME-accredited, web-based educational activities on T2D and obesity, touchIN CONVERSATION and touch MultiDisciplinary Team, were developed and made available on a free-to-access medical education website. Each activity comprised 3 videos lasting 10 to 15 minutes, which addressed learning objectives developed based on a review of published literature and faculty feedback. Participant satisfaction (Moore level 2) was evaluated using a postactivity questionnaire. For both activities, changes in knowledge and competence (Moore levels 3 and 4) were assessed using questionnaires completed by representative HCPs before or after participation in the activities. A second set of HCPs completed a questionnaire before and after engaging in activities that assessed changes in self-reported performance (Moore level 5).RESULTS:Each activity was viewed by approximately 6000 participants within 6 months. The participants expressed high levels of satisfaction (>80%) with both activities. Statistically significant improvements from baseline in knowledge and competence were reported following participation in touchIN CONVERSATION (mean score, SD before vs after activity: 4.36, 1.40 vs 5.42, 1.37; P<.001), with the proportion of learners answering at least six of 7 questions correctly, increasing from 22% (11/50) to 60% (30/50). A nonsignificant improvement in knowledge and competence was observed following participation in touch MultiDisciplinary Team (mean score, SD 4.36, 1.24 vs 4.58, 1.07; P=.35); however, baseline knowledge and competence were relatively high, where 80% of the respondents (40/50) answered at least four of 6 questions correctly. A significant improvement in HCP self-reported performance was observed in a combined analysis of both activities (mean score, SD 2.65, 1.32 vs 3.15, 1.26; P=.03), with the proportion of learners selecting the answer representing the best clinical option for all 4 questions increasing from 32% (11/34) to 59% (20/34) after the activity. Several unmet educational needs were self-reported or identified from the analysis of incorrectly answered questions, including setting individualized glycemic targets and the potential benefits of sodium-glucose cotransporter 2 inhibitor therapies.CONCLUSIONS:Short, case-based, web-based CME activities designed for HCPs to fit their clinical schedules achieved improvements in knowledge, competence, and self-reported performance in T2D management. Ongoing educational needs identified included setting individualized glycemic targets and the potential benefits of sodium-glucose cotransporter 2 inhibitor therapies.

Background: Different antiretroviral therapies (ARTs) may have differing effects on central nervous system (CNS) function. We assessed CNS pharmacodynamic effects of switching integrase inhibitors in people-with-HIV (PWH).Methods: PWH on tenofovir-DF/emtricitabine plus raltegravir 400 mg twice daily with suppressed plasma HIV RNA and without overt neuropsychiatric symptoms were randomly allocated on a 1:2 basis to remain on raltegravir or switch to dolutegravir 50 mg once daily for 120 days. Pharmacodynamic parameters assessed included cognitive function (z-score of 7 domains), patient-reported outcome measures (PROMs; PHQ-9 and Beck's depression questionnaires), cerebral metabolite ratios measured by proton magnetic resonance spectroscopy (H1-MRS) and plasma and cerebrospinal fluid (CSF) HIV RNA. Pharmacokinetic parameters were also assessed in plasma and CSF. Changes and factors associated with changes in pharmacodynamics parameters were assessed.Results:In 20 subjects (19 male, 14 white ethnicity, median age 43 years (IQR: 11.5) and CD4 + count 717 (SD: 298) cells/µL), over 120 days there were no statistically significant changes in cognitive function [mean z-score difference (95%CI) -0.004 (-0.38/0.37); p = 0.98], PROMs [PHQ-9 median score change: 0 in control arm, -0.5 switch arm (p = 0.57); Beck's depression questionnaire: -1.5 control arm, -1.0 switch arm (p = 0.38)], nor cerebral metabolite ratios between study arms. CSF HIV RNA was <5 copies/mL at baseline and day 120 in all subjects. Geometric mean pre-dose CSF dolutegravir concentration was 7.6 ng/mL (95% CI: 5.2-11.1).Conclusions:Switching integrase inhibitor in virologically suppressed PWH without overt neuropsychiatric symptoms resulted in no significant changes in an extensive panel of CNS pharmacodynamics parameters.

The mechanisms underlying central nervous system (CNS) toxicities in antiretroviral-treated persons living with HIV (PLWH) remain elusive. We investigated the associations between markers of tryptophan metabolism and measurements of CNS toxicity in PLWH. In a prospective study, virologically suppressed PLWH receiving efavirenz-containing antiretroviral regimens with ongoing CNS toxicity were switched to dolutegravir-containing regimens and followed up for 12 weeks. Plasma tryptophan and kynurenine concentrations and the kynurenine/tryptophan ratio were calculated. Ten CNS toxicities were graded according to the ACTG adverse events scale. Scores ranged from 0 (none) to 3 (severe) and were summed, giving a total from 0 to 30. Paired-samples t tests and linear mixed model analyses were conducted to assess changes in, and relationships between, laboratory and clinical parameters. Mean kynurenine plasma concentration increased from baseline to week 12 (2.15 to 2.50 μmol/L, p = 0.041). No significant changes were observed for tryptophan (54.74 to 56.42 μmol/L, p = 1.000) or kynurenine/tryptophan ratio (40.37 to 41.08 μmol/L, p = 0.276). Mean CNS toxicity score decreased from 10.00 to 4.63 (p < 0.001). Plasma kynurenine concentration correlated with CNS toxicity score: for every 1 μmol/L increase in kynurenine concentration observed, a 1.7 point decrease was observed in CNS toxicity score (p < 0.038). A similar trend was observed for the kynurenine/tryptophan ratio: for every 1 μmol/mmol increase observed in kynurenine/tryptophan ratio, a 0.1 point decrease was observed in CNS toxicity score (p = 0.054). Switching from efavirenz to dolutegravir was associated with increases in plasma kynurenine concentration and improvements in CNS toxicity scores. Underlying mechanisms explaining the rise in kynurenine concentrations need to be established.

Objectives:HIV-1 diversity is a major barrier in efficacious vaccine development.Different strains of HIV-1 are found in different regions of the globe; clade C in sub-Saharan Africa and clade B in the USA and Europe. A vaccine development and design approach has been to use a compilation of worldwide strains to try and develop a global vaccine. However, this approach so far has not resulted in an efficacious global vaccine. One reason for this could be that global strains might have differences to local strains that might be important for vaccine efficacy in a local population. Methods:We thus developed an approach that uses local strains to evaluate vaccine design strategies within a defined local population. We hypothesized that this approach would more effective in determining vaccine relevant immunogenicity to global strain approaches within a defined population. We tested a vaccine design approach that used local circulating strain on samples derived from the same population and compared it to approaches that used global circulating strains. Results/Conclusions:We show that the cohort-specific approach was able to trigger comparable immune responses to global approaches but with an added advantage of discovering cohort-unique immune triggers not detected by either of the global approaches.

HIV-1 controllers (HIC) are extremely rare patients with the ability to control viral replication, maintain unchanging CD4 T-cell count, and evade disease progression for extensive periods of time, in the absence of antiretroviral therapy. In order to establish the representation of key genetic correlates of atypical disease progression within a cohort of HIV-1+ individuals who control viral replication, we examine four-digit resolution HLA type and single-nucleotide polymorphisms (SNP) previously identified to be correlated to non-progressive infection, in strictly defined HIC. Clinical histories were examined to identify patients exhibiting HIC status. Genomic DNA was extracted, and high definition HLA typing and genome-wide SNP analysis was performed. Data were compared with frequencies of SNP in European long-term non-progressors (LTNP) and primary infection cohorts. HLA-B alleles associated with atypical disease progression were at very high frequencies in the group of five HIC studied. All four HIC of European ancestry were HLA-B*57+ and half were also HLA-B*27+. All HIC, including one of self-reported African ethnicity, had the HLA-Cw*0602 allele, and the HLA-DQ9 allele was present only in HIC of European ancestry. A median 95% of the top 19 SNP known to be associated with LTNP status was observed in European HIC (range 78-100%); 17/19 of the SNP considered mapped to chromosome 6 in the HLA region, whereas 2/19 mapped to chromosome 8. The HIC investigated here demonstrated high enrichment of HLA types and SNP previously associated with long-term non-progression. These findings suggest that the extreme non-progressive phenotype considered here is associated with a genetic signature characterized by a single-genetic unit centered around the HLA-B*57 haplotype and the possible additive effect of HLA-B*27.

The human immunodeficiency virus (HIV) accesses the central nervous system (CNS) early during infection, leading to HIV-associated cognitive impairment and establishment of a viral reservoir. Here, we describe a dichotomy in inflammatory responses in different CNS regions in simian immunodeficiency virus (SIV)-infected macaques, a model for HIV infection. We found increased expression of inflammatory genes and perivascular leukocyte infiltration in the midbrain of SIV-infected macaques. Conversely, the frontal lobe showed downregulation of inflammatory genes associated with interferon-γ and interleukin-6 pathways, and absence of perivascular cuffing. These immunologic alterations were not accompanied by differences in SIV transcriptional activity within the tissue. Altered expression of genes associated with neurotoxicity was observed in both midbrain and frontal lobe. The segregation of inflammatory responses to specific regions of the CNS may both account for HIV-associated neurological symptoms and constitute a critical hurdle for HIV eradication by shielding the CNS viral reservoir from antiviral immunity.

During pregnancy, the mother allows the immunologically distinct fetoplacental unit to develop and grow. Opinions are divided as to whether this represents a state of fetal-specific tolerance or of a generalized suppression of the maternal immune system. We hypothesized that antigen-specific T cell responses are modulated by an inhibitory T cell phenotype and modified dendritic cell (DC) phenotype in a gestation-dependent manner. We analyzed changes in surface markers of peripheral blood T cells, ex vivo antigen-specific T cell responses, indoleamine 2,3-dioxygenase (IDO) activity (kynurenine/tryptophan ratio, KTR), plasma neopterin concentration, and the in vitro expression of progesterone-induced blocking factor (PIBF) in response to peripheral blood mononuclear cell culture with progesterone. We found that mid gestation is characterized by reduced antigen-specific T cell responses associated with (1) predominance of effector memory over other T cell subsets; (2) upregulation of inhibitory markers (programmed death ligand 1); (3) heightened response to progesterone (PIBF); and (4) reduced proportions of myeloid DC and concurrent IDO activity (KTR). Conversely, antigen-specific T cell responses normalized in late pregnancy and were associated with increased markers of T cell activation (CD38, neopterin). However, these changes occur with a simultaneous upregulation of immune suppressive mechanisms including apoptosis (CD95), coinhibition (TIM-3), and immune regulation (IL-10) through the course of pregnancy. Together, our data suggest that immune tolerance dominates in the second trimester and that it is gradually reversed in the third trimester in association with immune activation as the end of pregnancy approaches.

OBJECTIVE:To explore the effects of microglial activation on brain function and structure, and its relationship with peripheral inflammatory markers, in treated, HIV-positive individuals, using in vivo [(11)C]PBR28 PET (to measure the 18 kDa translocator protein [TSPO]).METHODS:Cognitively healthy HIV-positive individuals on suppressive antiretroviral therapy and HIV-negative individuals (controls) underwent brain [(11)C]PBR28 PET and MRI. HIV-positive patients completed neuropsychological testing and CSF testing for chemokines. The concentration of bacterial ribosomal 16sDNA in plasma was measured as a marker of microbial translocation.RESULTS:HIV-positive individuals showed global increases in TSPO expression compared to controls (corrected p < 0.01), with significant regional increases in the parietal (p = 0.001) and occipital (p = 0.046) lobes and in the globus pallidus (p = 0.035). TSPO binding in the hippocampus, amygdala, and thalamus were associated with poorer global cognitive performance in tasks assessing verbal and visual memory (p < 0.05). Increased TSPO binding was associated with increased brain white matter diffusion MRI mean diffusivity in HIV-positive individuals, a lower CD4/CD8 ratio, and both high pretreatment HIV RNA and plasma concentration ribosomal 16s DNA (p < 0.05).CONCLUSIONS:Cognitively healthy HIV-positive individuals show evidence for a chronically activated brain innate immune response and elevated blood markers of microbial translocation despite effective control of plasma viremia. Increased brain inflammation is associated with poorer cognitive performance and white matter microstructural pathology, suggesting a possible role in cognitive impairments found in some HIV-positive patients despite effective treatment.

Objective Cognitive impairment (CI) and major depressive disorder (MDD) remain prevalent in treated HIV-1 disease; however, the pathogenesis remains elusive. A possible contributing mechanism is immune-mediated degradation of tryptophan (TRP) via the kynurenine (KYN) pathway, resulting in decreased production of serotonin and accumulation of TRP degradation products. We explored the association of these biochemical pathways and their relationship with CI and MDD in HIV-positive (HIV+) individuals. Methods In a cross-sectional analysis, concentrations of neopterin (NEO), tumor necrosis factor-alpha, TRP, KYN, KYN/TRP ratio, phenylalanine (PHE), tyrosine (TYR), PHE/TYR ratio, and nitrite were assessed in the cerebrospinal fluid (CSF) and plasma of HIV+( n = 91) and HIV-negative (HIV-) individuals ( n = 66). CI and MDD were assessed via a comprehensive neuropsychological test battery. A Global Deficit Score ≥0.5 was defined as CI. Nonparametric statistical analyses included Kruskal–Wallis and Mann–Whitney U tests, and multivariate logistic regression. Results Following Bonferroni correction, NEO concentrations were found to be greater in CSF and TRP concentration was found to be lower in the plasma of HIV+ versus HIV– individuals, including a subgroup of aviremic (defined as HIV-1 RNA <50 cps/mL) HIV+ participants receiving antiretroviral therapy ( n = 44). There was a nonsignificant trend toward higher KYN/TRP ratios in plasma in the HIV+ group ( P = 0.027; Bonferroni corrected α = 0.0027). In a logistic regression model, lower KYN/TRP ratios in plasma were associated with CI and MDD in the overall HIV+ group ( P = 0.038 and P = 0.063, respectively) and the aviremic subgroup ( P = 0.066 and P = 0.027, respectively), though this observation was not statistically significant following Bonferroni correction (Bonferroni corrected α = 0.0031). Conclusions We observed a trend toward lower KYN/TRP ratios in aviremic HIV+ patients with CI and MDD.

The case of Timothy Ray Brown, who received hematopoietic stem cell transplant (HSCT) from a CCR5-Δ32 donor to treat AIDS-related lymphoma, remains the only example of a patient cured from HIV infection [1]. HSCT from CCR5 wild-type donors failed to cure HIV in two other AIDS-related lymphoma patients, but delayed viral rebound after combined antiretroviral therapy (cART) interruption [2,3]. At least one of two conditions must be fulfilled to achieve HIV cure: elimination of all latent HIV reservoirs or protection of CD4+ T cells from de-novo infection. Purging viral reservoirs requires that all cells bearing functional HIV provirus are accessible for activation and susceptible to viral cytopathicity and/or immune-mediated clearance. For the latter, it is essential that HIV-specific cytotoxic T-lymphocyte (CTL) responses be restored [4]. Preventing infection of new targets may be more challenging. Transplants of rare heterologous human leukocyte antigen (HLA)-matched CCR5-Δ32 or autologous genetically modified CCR5-KO hematopoietic stem cell [5] may require immunoablation to ensure total resistance to infection. There is general consensus on the hypothesis that some degree of graft-vs-host (GVH) reactivity may have reduced the viral reservoir in the HSCT patients who showed delayed viremia rebound [5]. Thus, similar to the extensively studied graft-vs-leukemia phenomenon [6], a graft-vs-viral reservoir effect (GVVR) could target host cells that survived immunoablation, thus shrinking the HIV reservoir. Could GVVR be independently exploited of immunoablation? Would it be advantageous, and how could it be delivered and tested? Several independent reports spanning 40 years suggest a strategy for addressing these issues. Exposing nonablated, cART-treated HIV patients to HLA-allogeneic leukocytes could simultaneously induce GVVR; reactivate latent HIV reservoirs; enhance or restore host HIV-specific immunity; and activate restriction factors that prevent CD4+ T-cell infection (Fig. 1).Fig. 1: Schematic representation of the key mechanisms activated by allogeneic major histocompatibility complex recognition during graft-vs-host (GVH) and host-vs-graft (HVG) reactions in HIV-positive patients receiving combined antiretroviral therapy (cART).Infusion of leukocytes from allogeneic healthy uninfected donors in HIV-positive patients (hosts) receiving effective cART will target the latent viral reservoir by (a) GVH-mediated reactivation and clearance of latently infected cells (GVVR effect); (b) GVH and HVG-mediated eactivation of latently infected cells and purging by cytopathic effect under cART or HIV-specific cytotoxic T-lymphocyte (CTL) activity; and (c) HVG-mediated stimulation of CD4+ T-helper cells that activate HIV-specific CTL activity. (d) Protection of host and donor CD4+ T cells from de-novo infection by underlying cART and a combination of GVH/HVG-activated restriction factors.Approximately 1 : 1000 T lymphocytes recognize allogeneic major histocompatibility complex (MHC) molecules, 1000-fold more frequent than peptide-specific T lymphocytes [7]. MHC-allospecific T-helper cell responses are retained in most asymtpomatic HIV-infected patients [8], but these responses would be eliminated by immunoablation. Immunization with allogeneic leukocytes in immunocompetent women experiencing recurrent spontaneous abortion caused no major side-effects [9], and resulted in enhanced resistance of CD4+ T cells to in-vitro HIV infection [10]. The combined reactions of donor T cells against patient MHC (GVH) and of patient leukocytes against donor's MHC (host-vs-graft) could lead to HIV reactivation and enhanced presentation of retroviral peptides in deep anatomical sites (Fig. 1). Thus, activation of host latent murine leukemia retrovirus was reported in a murine GVH model, including latent provirus in bystander T cells that do not recognize allogeneic MHC [11]. Similar experiments in rats showed increased MHC expression in host epidermal cells, gut epithelium [12], and MHC-negative nervous tissue [13]. Treatment with allogeneic donor cells could also promote host HIV-specific CTL-mediated immunity (host-vs-viral reservoir) (Fig. 1). Thus, stimulation with allogeneic leukocytes restored T-cell-mediated help to autologous influenza virus-specific [14] and HIV-specific CTLs (M.C. and G.M.S., unpublished observations). Finally, stimulation with allogeneic MHC can activate a broad range of restriction factors (APOBEC3G, RANTES, MIP-1α/β, and CD8-derived suppressor factor) [10,15] that could synergize with cART to protect CD4+ cells from HIV during reservoir reactivation. Infusion of allogeneic cells into nonablated HIV-positive patients is less likely to cause GVH disease (GVHD) than HSCT [1–3]. The number and type of T cells infused and the number of infusions over time could be optimized to achieve GVVR, while abating the risk of GVHD. The strategy we propose can be tested in simian immunodeficiency virus (SIV)-infected macaques to determine whether the injection of T cells from uninfected HLA-mismatched macaques into ART-treated, SIV-infected animals results in increased MHC expression, recruitment of donor T cells, and activation of latent SIV in multiple tissues; enhancement of SIV-specific CTL responses; activation of innate antiretroviral factors; and ultimately spontaneous control of viremia after ART interruption. This animal model could also determine the half-life of injected allogeneic T cells to provide critical information on the cell number and frequency of infusions required, as well as monitor signs of GVHD or autoimmunity. HSCT with CCR5-defective cells proved successful in one case, but is unsuitable for large-scale application because of the risks posed by immunoablation, elevated costs of the procedure, and need for prophylaxis against opportunistic infections. Other strategies aimed at reactivating latent HIV reservoirs using modulators of gene expression and chromatin structure are being investigated, and might require supplementation with immunotherapy to revive HIV-specific T-cell responses [16]. By contrast, the combination of GVVR and host-vs-viral reservoir could simultaneously achieve both goals by exposing latently HIV-infected 'sleeper cells' to a crossfire from both host HIV-specific and donor allogeneic T cells. Acknowledgements The authors are grateful to Professor Robert Siliciano (Johns Hopkins University, Baltimore, Maryland, USA), Dr Steven Patterson and Dr Gareth Hardy (Imperial College London, London, UK), and Professor Robert B. Levy (University of Miami, Miami, Florida, USA) for their constructive review and criticism on the ideas presented in this manuscript. Conflicts of interest There are no conflicts of interest.

Plasmacytoid dendritic cells (pDC) are innate immunity effector cells which play a critical role in the transition from innate to adaptive immune response. Circulating blood pDC present an immature phenotype and can differentiate into either antigen-presenting cells (APC) or type I interferon (IFN-I)-producing cells (IPC). The immunoglobulin-like transcript (ILT)7 is a surface receptor expressed by immature pDC, and ILT7 cross-linking (XL-ILT7) inhibits IFN-I production by pDC in response to toll-like receptor (TLR)7 and 9 stimulation. We used peripheral blood mononuclear cells (PBMC) from healthy donors to test the effect of XL-ILT7 on 1) TLR7/9-mediated regulation of gut mucosal (α4β7 integrin) and lymph node (CCR7) migration markers; and 2) the maturation of pDC into APC. We found that XL-ILT7 mitigated the upregulation of CCR7 and enhanced that of β7 on TLR7/9-stimulated pDC. TLR7/9 stimulation induced upregulation of CD40, CD80 and CD86. CD40 expression was partially reduced by XL-ILT7, whereas CD86 was further enhanced. Plasmacytoid DC stimulated with TLR9 ligand in presence of XL-ILT7 retained the ability to induce T cell proliferation and activation in response to staphylococcal enterotoxin B (SEB) in pDC-T cell co-cultures. Our results suggest that XL-ILT7 favours the differentiation of immature pDC into APC rather than IPC.

HIV-1 causes a progressive impairment of immune function. HIV-2 is a naturally attenuated form of HIV, and HIV-2 patients display a slow-progressing disease. The leading hypothesis for the difference in disease phenotype between HIV-1 and HIV-2 is that more efficient T cell–mediated immunity allows for immune-mediated control of HIV-2 infection, similar to that observed in the minority of HIV-1–infected long-term nonprogressors. Understanding how HIV-1 and HIV-2 differentially influence the immune function may highlight critical mechanisms determining disease outcome. We investigated the effects of exposing primary human peripheral blood cells to HIV-1 or HIV-2 in vitro. HIV-2 induced a gene expression profile distinct from HIV-1, characterized by reduced type I IFN, despite similar upregulation of IFN-stimulated genes and viral restriction factors. HIV-2 favored plasmacytoid dendritic cell (pDC) differentiation into cells with an APC phenotype rather than IFN-α–producing cells. HIV-2, but not HIV-1, inhibited IFN-α production in response to CpG-A. The balance between pDC maturation into IFN-α–producing cells or development of an APC phenotype differentiates the early response against HIV-1 and HIV-2. We propose that divergent paths of pDC differentiation driven by HIV-1 and HIV-2 cause the observed differences in pathogenicity between the two viruses.

Background:Immune activation plays a key role in the immunopathogenesis of HIV-1 infection. Microbial translocation, secondary to loss of epithelial integrity and mucosal immune deficiency, is believed to contribute to systemic immune activation. Interleukin 22 maintains intestinal epithelial barrier integrity and stimulates the secretion of antimicrobial peptides that limit bacterial dissemination and intestinal inflammation. Interleukin 22 is secreted by CD4 T-helper (Th)22 cells independently of interleukin 17A and interferon . Th22 cells are characterized by the expression of chemokine receptors (CCR)4, CCR6, and CCR10.Methods:We analyzed the frequency of Th22, Th17, Th1, and CD4 T regulatory (Treg) cells, markers of immune activation (expression of CD38 on CD8 T cells, neopterin, soluble CD14), microbial translocation (lipopolysaccharide-binding protein and 16s ribosomal DNA), and indoleamine 2,3-dioxygenase 1 activity in peripheral blood of antiretroviral therapy (ART)-experienced and ART-naive HIV-1-infected patients and healthy controls.Results:We showed a significant reduction in the frequency of Th22 cells in HIV ART-naive patients compared with the healthy controls and HIV ART-experienced patients. We observed a shift away from Th22 and Th17 to Treg cells, which was partially reversed by effective ART. Markers of immune activation negatively correlated with Th22 and Th17 proportions, and with Th22:Treg and Th17:Treg ratios in ART-naive patients. Increased indoleamine 2,3-dioxygenase 1 activity negatively correlated with Th22:Treg and Th17:Treg ratios in the ART-naive group.Conclusions:Loss of Th22 cells and disruption in the balance of Th22 and Treg cells may contribute toward systemic immune activation and mucosal immune deficiency during HIV-1 infection.

The Ig-like transcript (ILT) 7 is a surface molecule selectively expressed by human plasmacytoid dendritic cells (pDCs). ILT7 cross-linking suppresses pDC activation and type I IFN (IFN-I) secretion following TLR7/9 engagement. The bone marrow stromal cell Ag 2 (BST2, aka HM1.24, tetherin, or CD317) is expressed by different cell types upon exposure to IFN-I and is a natural ligand for ILT7. In this study, we show that ILT7 expression decreased spontaneously in pDCs upon in vitro culture, which correlates with pDC differentiation measured as increased side scatter properties and CCR7 expression. TLR7/9 ligands, as well as HIV, induced BST2 upregulation on all tested cell types except T cells, which required TCR stimulation to respond to TLR9L-induced IFN-I. IFN-γ, IL-4, IL-10, and TNF-α had only marginal effects on BST2 expression in blood leukocytes compared with TLR9L. Preincubation with ILT7 cross-linking Ab inhibited IFN-I production in PBMCs treated with TLR7/9L or HIV, whereas BST2 blockade did not affect IFN-I responses even when BST2 upregulation was further boosted with TCR agonists or immunoregulatory cytokines. Our data indicate that BST2-mediated ILT7 cross-linking may act as a homeostatic regulatory mechanism on immature circulating pDC, rather than a negative feedback for activated mature pDCs that have downregulated ILT7.