Targeting the chemokine receptor CXCR4 with histamine analog to reduce inflammation in juvenile arthritis

Introduction

Among immune cells, activated monocytes play a detrimental role in chronic and viral-induced inflammatory pathologies, particularly in Juvenile Idiopathic Arthritis (JIA), a childhood rheumatoid arthritis (RA) disease. The uncontrolled activation of monocytes and excessive production of inflammatory factors contribute to the damage of bone-cartilage joints. Despite the moderate beneficial effect of current therapies and clinical trials, there is still a need for alternative strategies targeting monocytes to treat RA.

Methods

To explore such an alternative strategy, we investigated the effects of targeting the CXCR4 receptor using the histamine analog clobenpropit (CB). Monocytes were isolated from the blood and synovial fluids of JIA patients to assess CB's impact on their production of key inflammatory cytokines. Additionally, we administered daily intraperitoneal CB treatment to arthritic mice to evaluate its effects on circulating inflammatory cytokine levels, immune cell infiltrates, joints erosion, and bone resorption, as indicators of disease progression.

Results

Our findings demonstrated that CXCR4 targeting with CB significantly inhibited the spontaneous and induced-production of key inflammatory cytokines by monocytes isolated from JIA patients. Furthermore, CB treatment in a mouse model of collagen-induce arthritis resulted in a significant decrease in circulating inflammatory cytokine levels, immune cell infiltrates, joints erosion, and bone resorption, leading to a reduction in disease progression.

Discussion

In conclusion, targeting CXCR4 with the small amino compound CB shows promise as a therapeutic option for chronic and viral-induced inflammatory diseases, including RA. CB effectively regulated inflammatory cytokine production of monocytes, presenting a potential targeted approach with potential advantages over current therapies. These results warrant further research and clinical trials to explore the full therapeutic potential of targeting CXCR4 with CB-like molecules in the management of various inflammatory diseases.

Tuberculosis alters immune-metabolic pathways resulting in perturbed IL-1 responses

Tuberculosis (TB) remains a major public health problem and we lack a comprehensive understanding of how Mycobacterium tuberculosis (M. tb) infection impacts host immune responses. We compared the induced immune response to TB antigen, BCG and IL-1β stimulation between latently M. tb infected individuals (LTBI) and active TB patients. This revealed distinct responses between TB/LTBI at transcriptomic, proteomic and metabolomic levels. At baseline, we identified a novel immune-metabolic association between pregnane steroids, the PPARγ pathway and elevated plasma IL-1ra in TB. We observed dysregulated IL-1 responses after BCG stimulation in TB patients, with elevated IL-1ra responses being explained by upstream TNF differences. Additionally, distinct secretion of IL-1α/IL-1β in LTBI/TB after BCG stimulation was associated with downstream differences in granzyme mediated cleavage. Finally, IL-1β driven signalling was dramatically perturbed in TB disease but was completely restored after successful treatment. This study improves our knowledge of how immune responses are altered during TB disease, and may support the design of improved preventive and therapeutic tools, including host-directed strategies.

Understanding lactate sensing and signalling

Metabolites generated from cellular and tissue metabolism have been rediscovered in recent years as signalling molecules. They may act as cofactor of enzymes or be linked to proteins as post-translational modifiers. They also act as ligands for specific receptors, highlighting that their neglected functions have, in fact, a long standing in evolution. Lactate is one such metabolite that has been considered for long time a waste product of metabolism devoid of any biological function. However, in the past 10 years, lactate has gained much attention in several physio-pathological processes. Mechanisms of sensing and signalling have been discovered and implicated in a broad range of diseases, from cancer to inflammation and fibrosis, providing opportunities for novel therapeutic avenues. Here, we review some of the most recently discovered mechanisms of lactate sensing and signalling.

Early IFNβ secretion determines variable downstream IL-12p70 responses upon TLR4 activation

The interleukin-12 (IL-12) family comprises the only heterodimeric cytokines mediating diverse functional effects. We previously reported a striking bimodal IL-12p70 response to lipopolysaccharide (LPS) stimulation in healthy donors. Herein, we demonstrate that interferon β (IFNβ) is a major upstream determinant of IL-12p70 production, which is also associated with numbers and activation of circulating monocytes. Integrative modeling of proteomic, genetic, epigenomic, and cellular data confirms IFNβ as key for LPS-induced IL-12p70 and allowed us to compare the relative effects of each of these parameters on variable cytokine responses. Clinical relevance of our findings is supported by reduced IFNβ-IL-12p70 responses in patients hospitalized with acute severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection or chronically infected with hepatitis C (HCV). Importantly, these responses are resolved after viral clearance. Our systems immunology approach defines a better understanding of IL-12p70 and IFNβ in healthy and infected persons, providing insights into how common genetic and epigenetic variation may impact immune responses to bacterial infection.

Variability in primary Sjögren's syndrome is driven by interferon alpha, and genetically associated with the class II HLA DQ locus

OBJECTIVE

Primary Sjögren's syndrome (pSS) is the second most frequent systemic autoimmune disease affecting 0.1% of the general population. To characterize the molecular and clinical variability across pSS patients, we integrated transcriptomic, proteomic, cellular and genetic data with clinical phenotypes in a cohort of 351 pSS patients.

METHODS

Blood transcriptomes and genotypes of 351 pSS patients from a multi-center prospective clinical cohort were analyzed. Replication of the transcriptomic results was performed using 3 independent cohorts (n=462 patients). Circulating IFN-alpha (IFNɑ) and IFN-gamma (IFNγ) protein concentrations were determined using digital ELISA.

RESULTS

Transcriptomic analysis of the prospective cohort showed a strong IFN gene signature in more than half of the patients. This finding was replicated in three independent cohorts. As gene expression analysis did not discriminate between type I and II interferons, we applied digital ELISA to demonstrate that the IFN transcriptomic signature was driven by circulating IFNɑ, and not IFNγ, protein levels. IFNɑ protein levels, detectable in 75% of patients, were significantly associated with clinical and immunological features of disease activity at enrollment, and with increased frequency of systemic complications during the 5-year follow-up. Genetic analysis revealed a significant association between IFNɑ protein levels, a MHC-II haplotype and anti-SSA antibody. Additional cellular analysis revealed that a MHC-II HLA-DQ locus acts through upregulation of HLA II molecules on conventional DCs.

CONCLUSIONS

The present analysis identified the predominance of IFNα as driver of pSS variability and revealed an association with HLA gene polymorphisms.

Defects in mucosal immunity and nasopharyngeal dysbiosis in HSC-transplanted SCID patients with IL2RG/JAK3 deficiency

Both innate and adaptive lymphocytes have critical roles in mucosal defense that contain commensal microbial communities and protect against pathogen invasion. Here we characterize mucosal immunity in patients with severe combined immunodeficiency (SCID) receiving hematopoietic stem cell transplantation (HSCT) with or without myeloablation. We confirmed that pretransplant conditioning had an impact on innate (natural killer and innate lymphoid cells) and adaptive (B and T cells) lymphocyte reconstitution in these patients with SCID and now show that this further extends to generation of T helper 2 and type 2 cytotoxic T cells. Using an integrated approach to assess nasopharyngeal immunity, we identified a local mucosal defect in type 2 cytokines, mucus production, and a selective local immunoglobulin A (IgA) deficiency in HSCT-treated SCID patients with genetic defects in IL2RG/GC or JAK3. These patients have a reduction in IgA-coated nasopharyngeal bacteria and exhibit microbial dysbiosis with increased pathobiont carriage. Interestingly, intravenous immunoglobulin replacement therapy can partially normalize nasopharyngeal immunoglobulin profiles and restore microbial communities in GC/JAK3 patients. Together, our results suggest a potential nonredundant role for type 2 immunity and/or of local IgA antibody production in the maintenance of nasopharyngeal microbial homeostasis and mucosal barrier function.

Machine Learning-Based Single Cell and Integrative Analysis Reveals That Baseline mDC Predisposition Correlates With Hepatitis B Vaccine Antibody Response

Vaccination to prevent infectious disease is one of the most successful public health interventions ever developed. And yet, variability in individual vaccine effectiveness suggests that a better mechanistic understanding of vaccine-induced immune responses could improve vaccine design and efficacy. We have previously shown that protective antibody levels could be elicited in a subset of recipients with only a single dose of the hepatitis B virus (HBV) vaccine and that a wide range of antibody levels were elicited after three doses. The immune mechanisms responsible for this vaccine response variability is unclear. Using single cell RNA sequencing of sorted innate immune cell subsets, we identified two distinct myeloid dendritic cell subsets (NDRG1-expressing mDC2 and CDKN1C-expressing mDC4), the ratio of which at baseline (pre-vaccination) correlated with the immune response to a single dose of HBV vaccine. Our results suggest that the participants in our vaccine study were in one of two different dendritic cell dispositional states at baseline – an NDRG2-mDC2 state in which the vaccine elicited an antibody response after a single immunization or a CDKN1C-mDC4 state in which the vaccine required two or three doses for induction of antibody responses. To explore this correlation further, genes expressed in these mDC subsets were used for feature selection prior to the construction of predictive models using supervised canonical correlation machine learning. The resulting models showed an improved correlation with serum antibody titers in response to full vaccination. Taken together, these results suggest that the propensity of circulating dendritic cells toward either activation or suppression, their “dispositional endotype” at pre-vaccination baseline, could dictate response to vaccination.

Host Immune-Metabolic Adaptations Upon Mycobacterial Infections and Associated Co-Morbidities

Mycobacterial diseases are a major public health challenge. Their causative agents include, in order of impact, members of the Mycobacterium tuberculosis complex (causing tuberculosis), Mycobacterium leprae (causing leprosy), and non-tuberculous mycobacterial pathogens including Mycobacterium ulcerans. Macrophages are mycobacterial targets and they play an essential role in the host immune response to mycobacteria. This review aims to provide a comprehensive understanding of the immune-metabolic adaptations of the macrophage to mycobacterial infections. This metabolic rewiring involves changes in glycolysis and oxidative metabolism, as well as in the use of fatty acids and that of metals such as iron, zinc and copper. The macrophage metabolic adaptations result in changes in intracellular metabolites, which can post-translationally modify proteins including histones, with potential for shaping the epigenetic landscape. This review will also cover how critical tuberculosis co-morbidities such as smoking, diabetes and HIV infection shape host metabolic responses and impact disease outcome. Finally, we will explore how the immune-metabolic knowledge gained in the last decades can be harnessed towards the design of novel diagnostic and therapeutic tools, as well as vaccines.

Lactate cross-talk in host-pathogen interactions

Lactate is the main product generated at the end of anaerobic glycolysis or during the Warburg effect and its role as an active signalling molecule is increasingly recognised. Lactate can be released and used by host cells, by pathogens and commensal organisms, thus being essential for the homeostasis of host-microbe interactions. Infection can alter this intricate balance, and the presence of lactate transporters in most human cells including immune cells, as well as in a variety of pathogens (including bacteria, fungi and complex parasites) demonstrates the importance of this metabolite in regulating host-pathogen interactions. This review will cover lactate secretion and sensing in humans and microbes, and will discuss the existing evidence supporting a role for lactate in pathogen growth and persistence, together with lactate's ability to impact the orchestration of effective immune responses. The ubiquitous presence of lactate in the context of infection and the ability of both host cells and pathogens to sense and respond to it, makes manipulation of lactate a potential novel therapeutic strategy. Here, we will discuss the preliminary research that has been carried out in the context of cancer, autoimmunity and inflammation.

Altered Immune Phenotypes and HLA-DQB1 Gene Variation in Multiple Sclerosis Patients Failing Interferon β Treatment

Background

Interferon beta (IFNβ) has been prescribed as a first-line disease-modifying therapy for relapsing-remitting multiple sclerosis (RRMS) for nearly three decades. However, there is still a lack of treatment response markers that correlate with the clinical outcome of patients.

Aim

To determine a combination of cellular and molecular blood signatures associated with the efficacy of IFNβ treatment using an integrated approach.

Methods

The immune status of 40 RRMS patients, 15 of whom were untreated and 25 that received IFNβ1a treatment (15 responders, 10 non-responders), was investigated by phenotyping regulatory CD4⁺ T cells and naïve/memory T cell subsets, by measurement of circulating IFNα/β proteins with digital ELISA (Simoa) and analysis of ~600 immune related genes including 159 interferon-stimulated genes (ISGs) with the Nanostring technology. The potential impact of HLA class II gene variation in treatment responsiveness was investigated by genotyping HLA-DRB1, -DRB3,4,5, -DQA1, and -DQB1, using as a control population the Milieu Interieur cohort of 1,000 French healthy donors.

Results

Clinical responders and non-responders displayed similar plasma levels of IFNβ and similar ISG profiles. However, non-responders mainly differed from other subject groups with reduced circulating naïve regulatory T cells, enhanced terminally differentiated effector memory CD4⁺ T_EMRA cells, and altered expression of at least six genes with immunoregulatory function. Moreover, non-responders were enriched for HLA-DQB1 genotypes encoding DQ8 and DQ2 serotypes. Interestingly, these two serotypes are associated with type 1 diabetes and celiac disease. Overall, the immune signatures of non-responders suggest an active disease that is resistant to therapeutic IFNβ, and in which CD4⁺ T cells, likely restricted by DQ8 and/or DQ2, exert enhanced autoreactive and bystander inflammatory activities.

Systems Biology Methods Applied to Blood and Tissue for a Comprehensive Analysis of Immune Response to Hepatitis B Vaccine in Adults

Conventional vaccine design has been based on trial-and-error approaches, which have been generally successful. However, there have been some major failures in vaccine development and we still do not have highly effective licensed vaccines for tuberculosis, HIV, respiratory syncytial virus, and other major infections of global significance. Approaches at rational vaccine design have been limited by our understanding of the immune response to vaccination at the molecular level. Tools now exist to undertake in-depth analysis using systems biology approaches, but to be fully realized, studies are required in humans with intensive blood and tissue sampling. Methods that support this intensive sampling need to be developed and validated as feasible. To this end, we describe here a detailed approach that was applied in a study of 15 healthy adults, who were immunized with hepatitis B vaccine. Sampling included ~350 mL of blood, 12 microbiome samples, and lymph node fine needle aspirates obtained over a ~7-month period, enabling comprehensive analysis of the immune response at the molecular level, including single cell and tissue sample analysis. Samples were collected for analysis of immune phenotyping, whole blood and single cell gene expression, proteomics, lipidomics, epigenetics, whole blood response to key immune stimuli, cytokine responses, in vitro T cell responses, antibody repertoire analysis and the microbiome. Data integration was undertaken using different approaches-NetworkAnalyst and DIABLO. Our results demonstrate that such intensive sampling studies are feasible in healthy adults, and data integration tools exist to analyze the vast amount of data generated from a multi-omics systems biology approach. This will provide the basis for a better understanding of vaccine-induced immunity and accelerate future rational vaccine design.

Immune profiling enables stratification of patients with active TB disease or M. tuberculosis infection

Background

Tuberculosis (TB) is caused by Mycobacterium tuberculosis (Mtb) infection and is a major public health problem. Clinical challenges include the lack of a blood-based test for active disease. Current blood-based tests, such as QuantiFERON (QFT) do not distinguish active TB disease from asymptomatic Mtb infection.

Methods

We hypothesized that TruCulture, an immunomonitoring method for whole-blood stimulation, could discriminate active disease from latent Mtb infection (LTBI). We stimulated whole blood from patients with active TB and compared with LTBI donors. Mtb-specific antigens and live bacillus Calmette-Guérin (BCG) were used as stimuli, with direct comparison to QFT. Protein analyses were performed using conventional and digital enzyme-linked immunosorbent assay (ELISA), as well as Luminex.

Results

TruCulture showed discrimination of active TB cases from LTBI (P < .0001, AUC = .81) compared with QFT (P = .45, AUC = .56), based on an interferon γ (IFNγ) readout after Mtb antigen (Ag) stimulation. This result was replicated in an independent cohort (AUC = .89). In exploratory analyses, TB stratification could be further improved by the Mtb antigen to BCG IFNγ ratio (P < .0001, AUC = .91). Finally, the combination of digital ELISA and transcriptional analysis showed that LTBI donors with high IFNγ clustered with patients with TB, suggesting the possibility to identify subclinical disease.

Conclusions

TruCulture offers a next-generation solution for whole-blood stimulation and immunomonitoring with the possibility to discriminate active and latent infection.

Innate immune stimulation of whole blood reveals IFN-1 hyper-responsiveness in type 1 diabetes

AIMS/HYPOTHESIS

Self-antigen-specific T cell responses drive type 1 diabetes pathogenesis, but alterations in innate immune responses are also critical and not as well understood. Innate immunity in human type 1 diabetes has primarily been assessed via gene-expression analysis of unstimulated peripheral blood mononuclear cells, without the immune activation that could amplify disease-associated signals. Increased responsiveness in each of the two main innate immune pathways, driven by either type 1 IFN (IFN-1) or IL-1, have been detected in type 1 diabetes, but the dominant innate pathway is still unclear. This study aimed to determine the key innate pathway in type 1 diabetes and assess the whole blood immune stimulation assay as a tool to investigate this.

METHODS

The TruCulture whole blood ex vivo stimulation assay, paired with gene expression and cytokine measurements, was used to characterise changes in the stimulated innate immune response in type 1 diabetes. We applied specific cytokine-induced signatures to our data, pre-defined from the same assays measured in a separate cohort of healthy individuals. In addition, NOD mice were stimulated with CpG and monocyte gene expression was measured.

RESULTS

Monocytes from NOD mice showed lower baseline vs diabetes-resistant B6.g7 mice, but higher induced IFN-1-associated gene expression. In human participants, ex vivo whole blood stimulation revealed higher induced IFN-1 responses in type 1 diabetes, as compared with healthy control participants. In contrast, neither the IL-1-induced gene signature nor response to the adaptive immune stimulant Staphylococcal enterotoxin B were significantly altered in type 1 diabetes samples vs healthy control participants. Targeted gene-expression analysis showed that this enhanced IFN response was specific to IFN-1, as IFN-γ-driven responses were not significantly different.

CONCLUSIONS/INTERPRETATION

Our study identifies increased responsiveness to IFN-1 as a feature of both the NOD mouse model of autoimmune diabetes and human established type 1 diabetes. A stimulated IFN-1 gene signature may be a potential biomarker for type 1 diabetes and used to evaluate the effects of therapies targeting this pathway.

DATA AVAILABILITY

Mouse gene expression data are found in the gene expression omnibus (GEO) repository, accession GSE146452 ( www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE146452 ). Nanostring count data from the human experiments were deposited in the GEO repository, accession GSE146338 ( www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE146338 ). Data files and R code for all analyses are available at https://github.com/rodriguesk/T1D_truculture_diabetologia . Graphical abstract.

Plasma Type I IFN Protein Concentrations in Human Tuberculosis

Tuberculosis (TB) remains one of the leading causes of mortality worldwide, and a lack of understanding of basic disease pathogenesis is hampering development of new vaccines and treatments. Multiple studies have previously established a role for type I interferon (IFN) in TB disease. Type I IFNs are critical immune mediators for host responses to viral infection, yet their specific influence in bacterial infection remains unclear. As IFN-stimulated genes (ISGs) can have both stimulatory and inhibitory effects on immune function, clarifying the role of type I interferon in TB remains an important question. The quantification of interferon proteins in the circulation of patients has been restricted until the recent development of digital ELISA. To test the hypothesis that patients with active TB disease have elevated circulating type I IFN we quantified plasma IFNα and β proteins with Simoa digital ELISA in patients with active disease and asymptomatic M. tuberculosis infection. Strikingly no differences were observed between these two groups, while plasma from acute influenza infection revealed significantly higher plasma levels of both IFNα and IFNβ proteins. These results suggest a discordance between ISG mRNA expression by blood leukocytes and circulating type I IFN in TB.

Development and clinical validation of the Genedrive point-of-care test for qualitative detection of hepatitis C virus

OBJECTIVE

Recently approved direct acting antivirals provide transformative therapies for chronic hepatitis C virus (HCV) infection. The major clinical challenge remains to identify the undiagnosed patients worldwide, many of whom live in low-income and middle-income countries, where access to nucleic acid testing remains limited. The aim of this study was to develop and validate a point-of-care (PoC) assay for the qualitative detection of HCV RNA.

DESIGN

We developed a PoC assay for the qualitative detection of HCV RNA on the PCR Genedrive instrument. We validated the Genedrive HCV assay through a case-control study comparing results with those obtained with the Abbott RealTime HCV test.

RESULTS

The PoC assay identified all major HCV genotypes, with a limit of detection of 2362 IU/mL (95% CI 1966 to 2788). Using 422 patients chronically infected with HCV and 503 controls negative for anti-HCV and HCV RNA, the Genedrive HCV assay showed 98.6% sensitivity (95% CI 96.9% to 99.5%) and 100% specificity (95% CI 99.3% to 100%) to detect HCV. In addition, melting peak ratiometric analysis demonstrated proof-of-principle for semiquantification of HCV. The test was further validated in a real clinical setting in a resource-limited country.

CONCLUSION

We report a rapid, simple, portable and accurate PoC molecular test for HCV, with sensitivity and specificity that fulfils the recent FIND/WHO Target Product Profile for HCV decentralised testing in low-income and middle-income countries. This Genedrive HCV assay may positively impact the continuum of HCV care from screening to cure by supporting real-time treatment decisions.

TRIAL REGISTRATION NUMBER

NCT02992184 .

Immune response biomarkers in human and veterinary research

Biomarkers are increasingly utilised in biological research and clinical practice for diagnosis of disease, monitoring of therapeutic prognosis, or as end points in clinical studies. Cytokines are small molecules that orchestrate immune responses and as such have great potential as biomarkers for both human and veterinary fields. Given the ease of sampling in the blood, and their high prevalence in clinical applications we will focus on protein detection as an area for biomarker discovery. This is facilitated by new technological developments such as digital ELISA that have led to significant increases in sensitivity. Two highly relevant examples include type I interferons, namely IFNα, that is now directly quantifiable by digital ELISA from biological samples. The application of this approach to the study of the unique bat interferon response may reveal novel findings with applications in both human and veterinary research. As a second example we will describe the use of CXCL10 as a disease biomarker in Tuberculosis, highlighting findings from human and mouse studies that should be considered in veterinary research. In summary, we describe how cytokines may be applied as novel biomarkers and illustrate two key examples where human and veterinary research may complement each other in line with the One Health objectives.

Development and Validation of an Ultrasensitive Single Molecule Array Digital Enzyme-linked Immunosorbent Assay for Human Interferon-α

The main aim of this protocol is to describe the development and validation of an interferon (IFN)-α single molecule array digital Enzyme-Linked ImmunoSorbent Assay (ELISA) assay. This system enables the quantification of human IFN-α protein with unprecedented sensitivity, and with no cross-reactivity for other species of IFN. The first key step of the protocol is the choice of the antibody pair, followed by the conjugation of the capture antibody to paramagnetic beads, and biotinylation of the detection antibody. Following this step, different parameters such as assay configuration, detector antibody concentration, and buffer composition can be modified until optimum sensitivity is achieved. Finally, specificity and reproducibility of the method are assessed to ensure confidence in the results. Here, we developed an IFN-α single molecule array assay with a limit of detection of 0.69 fg/mL using high-affinity autoantibodies isolated from patients with biallelic mutations in the autoimmune regulator (AIRE) protein causing autoimmune polyendocrinopathy syndrome type 1/autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APS1/APECED). Importantly, these antibodies enabled detection of all 13 IFN-α subtypes. This new methodology allows the detection and quantification of IFN-α protein in human biological samples at attomolar concentrations for the first time. Such a tool will be highly useful in monitoring the levels of this cytokine in human health and disease states, most particularly infection, autoimmunity, and autoinflammation.

Expression of lectin-like transcript-1 in human tissues

Background: Receptor-ligand pairs of C-type lectin-like proteins have been shown to play an important role in cross talk between lymphocytes, as well as in immune responses within concrete tissues and structures, such as the skin or the germinal centres. The CD161-Lectin-like Transcript 1 (LLT1) pair has gained particular attention in recent years, yet a detailed analysis of LLT1 distribution in human tissue is lacking. One reason for this is the limited availability and poor characterisation of anti-LLT1 antibodies. Methods: We assessed the staining capabilities of a novel anti-LLT1 antibody clone (2H7), both by immunohistochemistry and flow cytometry, showing its efficiency at LLT1 recognition in both settings. We then analysed LLT1 expression in a wide variety of human tissues. Results: We found LLT1 expression in circulating B cells and monocytes, but not in lung and liver-resident macrophages. We found strikingly high LLT1 expression in immune-privileged sites, such as the brain, placenta and testes, and confirmed the ability of LLT1 to inhibit NK cell function. Conclusions: Overall, this study contributes to the development of efficient tools for the study of LLT1. Moreover, its expression in different healthy human tissues and, particularly, in immune-privileged sites, establishes LLT1 as a good candidate as a regulator of immune responses.

CD161(int)CD8+ T cells: a novel population of highly functional, memory CD8+ T cells enriched within the gut

The C-type lectin-like receptor CD161 is expressed by lymphocytes found in human gut and liver, as well as blood, especially natural killer (NK) cells, T helper 17 (Th17) cells, and a population of unconventional T cells known as mucosal-associated invariant T (MAIT) cells. The association of high CD161 expression with innate T-cell populations including MAIT cells is established. Here we show that CD161 is also expressed, at intermediate levels, on a prominent subset of polyclonal CD8+ T cells, including antiviral populations that display a memory phenotype. These memory CD161(int)CD8+ T cells are enriched within the colon and express both CD103 and CD69, markers associated with tissue residence. Furthermore, this population was characterized by enhanced polyfunctionality, increased levels of cytotoxic mediators, and high expression of the transcription factors T-bet and eomesodermin (EOMES). Such populations were induced by novel vaccine strategies based on adenoviral vectors, currently in trial against hepatitis C virus. Thus, intermediate CD161 expression marks potent polyclonal, polyfunctional tissue-homing CD8+ T-cell populations in humans. As induction of such responses represents a major aim of T-cell prophylactic and therapeutic vaccines in viral disease and cancer, analysis of these populations could be of value in the future.

LLT1 and CD161 Expression in Human Germinal Centers Promotes B Cell Activation and CXCR4 Downregulation

Germinal centers (GCs) are microanatomical structures critical for the development of high-affinity Abs and B cell memory. They are organized into two zones, light and dark, with coordinated roles, controlled by local signaling. The innate lectin-like transcript 1 (LLT1) is known to be expressed on B cells, but its functional role in the GC reaction has not been explored. In this study, we report high expression of LLT1 on GC-associated B cells, early plasmablasts, and GC-derived lymphomas. LLT1 expression was readily induced via BCR, CD40, and CpG stimulation on B cells. Unexpectedly, we found high expression of the LLT1 ligand, CD161, on follicular dendritic cells. Triggering of LLT1 supported B cell activation, CD83 upregulation, and CXCR4 downregulation. Overall, these data suggest that LLT1–CD161 interactions play a novel and important role in B cell maturation within the GC in humans.