Association of the LILRA3 deletion with B-NHL and functional characterization of the immunostimulatory molecule

Leukocyte Ig-like receptor A3 facilitates inflammation, migration and invasion of synovial tissue-derived fibroblasts via ERK/JNK activation

OBJECTIVE

Leukocyte Ig-like receptor A3 (LILRA3) is a soluble receptor belongs to the immunoglobulin superfamily. Our previous studies demonstrated that LILRA3 is a common genetic risk for multiple autoimmune diseases, including RA. Functional LILRA3 conferred increased risk of joint destruction in patients with early RA. We undertook this study to further investigate the pathological role of LILRA3 in joint inflammation of RA.

METHODS

Soluble LILRA3 was measured by ELISA. LILRA3 plasmids were transfected into human fibroblast-like synoviocytes (FLSs) using electroporation. Activation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) was determined by western blots. Cytokine transcripts were quantified by real-time PCR. Migratory and invasive capacities of FLSs were evaluated using transwell migration and Matrigel invasion assays. FLS apoptosis was analysed using flow cytometry. Colocalization of LILRA3, LILRB1 and HLA-G in RA-FLSs was visualized by immunofluorescence staining.

RESULTS

Soluble LILRA3 was specifically expressed in synovial fluid and serum LILRA3 was significantly increased and positively correlated with disease activity/severity in RA patients. LILRA3 induced an increased expression of IL-6, IL-8 and MMP3 in RA-FLSs. In vitro LILRA3 stimulation or overexpression promoted RA-FLS migration and invasion, and enhanced phosphorylation of ERK/JNK. Inhibition of ERK/JNK resulted in suppression of IL-6/IL-8 expression in LILRA3-stimulated RA-FLSs. LILRA3 was co-localized with its homologue LILRB1 and shared ligand HLA-G in RA-FLSs.

CONCLUSION

The present study provides the first evidence that soluble LILRA3 is a novel proinflammatory mediator involved in synovial inflammation by promoting RA-FLS activation, migration and invasion, probably through the ERK/JNK signalling pathways.

Human leukocyte immunoglobulin-like receptors in health and disease

Human leukocyte immunoglobulin (Ig)-like receptors (LILR) are a family of 11 innate immunomodulatory receptors, primarily expressed on lymphoid and myeloid cells. LILRs are either activating (LILRA) or inhibitory (LILRB) depending on their associated signalling domains (D). With the exception of the soluble LILRA3, LILRAs mediate immune activation, while LILRB1-5 primarily inhibit immune responses and mediate tolerance. Abnormal expression and function of LILRs is associated with a range of pathologies, including immune insufficiency (infection and malignancy) and overt immune responses (autoimmunity and alloresponses), suggesting LILRs may be excellent candidates for targeted immunotherapies. This review will discuss the biology and clinical relevance of this extensive family of immune receptors and will summarise the recent developments in targeting LILRs in disease settings, such as cancer, with an update on the clinical trials investigating the therapeutic targeting of these receptors.

Biomarkers of lymphoma in Sjögren's syndrome: what's the latest?

INTRODUCTION

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease standing in the crossroads of autoimmunity and lymphomagenesis, characterized by chronic B-cell hyperactivity and ectopic lymphoid tissue neoformation, potentially driving lymphoid malignant transformation. Lymphoma development is considered the most serious complication of pSS.

AREAS COVERED: “

Old-classical" biomarkers (clinical, serological, hematological, and histological) validated in the past are analyzed under the perspective of recently published research. Biomarkers that have emerged during the last decade are subdivided to "old-new" and "newly proposed-novel" ones, including biomarkers pathophysiologically related to B-cell differentiation, lymphoid organization, and immune responses, identified in serum and tissue, both at genetic and protein level. Upcoming new imaging biomarkers, promising for further patient stratification, are also analyzed.

EXPERT OPINION

Salivary gland enlargement and cryoglobulinemia still remain the best validated "classical-old" biomarkers for lymphoma development. Though new biomarkers still need to be validated, some can be used for the identification of high-risk patients long before lymphoma diagnosis, some might be more relevant in distinct age subgroups, while others have an added value in the assessment of lymphoma remission or relapse. Future development of composite indices integrating old and recently proposed biomarkers could contribute to a more precise lymphoma prediction model.

Association of the Leukocyte Immunoglobulin-like Receptor A3 Gene With Neutrophil Activation and Disease Susceptibility in Adult-Onset Still's Disease

Objective

Adult‐onset Still’s disease (AOSD) is a severe autoinflammatory disease. Neutrophil activation with enhanced neutrophil extracellular trap (NET) formation is involved in the pathogenesis of AOSD. Functional leukocyte immunoglobulin‐like receptor A3 (LIR‐A3; gene name LILRA3) has been reported to be associated with many autoimmune diseases. We aimed to investigate the association of LILRA3 with disease susceptibility and neutrophil activation in AOSD.

Methods

The LILRA3 deletion polymorphism and its tagging single‐nucleotide polymorphism rs103294 were genotyped in 164 patients with AOSD and 305 healthy controls. The impact of LILRA3 on clinical features and messenger RNA expression was evaluated. Plasma levels of LIR‐A3 were detected using enzyme‐linked immunosorbent assay (ELISA), and the correlation between LIR‐A3 plasma levels and disease activity and levels of circulating NET‐DNA was investigated. LIR‐A3–induced NETs were determined using PicoGreen double‐stranded DNA dye and immunofluorescence analysis in human neutrophils and a neutrophil‐like differentiated NB4 cell line transfected with LIR‐B2 small interfering RNA.

Results

The findings from genotyping demonstrated that functional LILRA3 was a risk factor for AOSD (11% in AOSD patients versus 5.6% in healthy controls; odds ratio 2.089 [95% confidence interval 1.030–4.291], P = 0.034), and associated with leukocytosis (P = 0.039) and increased levels of circulating neutrophils (P = 0.027). Functional LILRA3 messenger RNA expression was higher in the peripheral blood mononuclear cells (P < 0.0001) and neutrophils (P < 0.001) of LILRA3^+/+ patients. Plasma levels of LIR‐A3 were elevated in patients with AOSD (P < 0.0001) and correlated with disease activity indicators and levels of circulating NET–DNA complexes. Finally, enhanced NET formation was identified in neutrophils from healthy controls and patients with inactive AOSD after stimulation of the neutrophils with LIR‐A3. Moreover, NET formation was impaired in NB4 cells after knockdown of LILRB2 gene expression.

Conclusion

Our study provides the first evidence that functional LILRA3 is a novel genetic risk factor for the development of AOSD and that functional LIR‐A3 may play a pathogenic role by inducing formation of NETs.

Upregulated expression of leukocyte immunoglobulin-like receptor A3 in patients with severe aplastic anemia

Severe aplastic anemia (SAA) is a rare and potentially life-threatening disease characterized by pancytopenia and bone marrow (BM) hypoplasia. In a previous study by our group, increased expression of leukocyte immunoglobulin-like receptors A (LILRA), LILRA3 in myeloid dendritic cells (mDCs) and LILRA5 in CD34⁺ cells in SAA was detected using proteomics techniques, highlighting their potential role in disease pathogenesis. In the present study, the expression of LILRA1-6 mRNA was assessed in the BM mononuclear cells of patients with SAA using reverse transcription-quantitative (RT-q)PCR. The expression of homogenic LILRA3 and LILRA5 isoform on mDCs, as well as CD34⁺, CD3⁺CD8⁺, CD19⁺ and CD14⁺ cells, was detected using flow cytometry. mDCs were then induced, cultured and sorted. The expression of LILRA3 was confirmed using RT-qPCR and western blot analyses. The serum levels of soluble LILRA3 were measured using ELISA. Furthermore, the relationship between LILRA3 expression and disease severity was assessed. The results indicated increased LILRA3 mRNA expression in patients with SAA. The percentage of LILRA3⁺ in BM mDCs and CD34⁺ cells was increased. Compared with controls, the relative LILRA3 mRNA expression and the relative protein intensity were highly increased in SAA mDCs. The serum LILRA3 levels in patients with SAA were also increased. The proportion of LILRA3⁺CD11C⁺ human leukocyte antigen (HLA)-DR⁺/CD11C⁺HLA-DR⁺ cells was positively correlated with the ratio of LILRA3⁺CD34⁺/CD34⁺ cells and the expression of LILRA3 mRNA. Taken together, the expression of LILRA3 on mDCs of patients with SAA was increased, which may affect the function of mDCs. LILRA3 may have a significant role in the immune pathogenesis of SAA.

Leukocyte Immunoglobulin-Like Receptor A3 (LILRA3): A Novel Marker for Lymphoma Development among Patients with Young Onset Sjogren's Syndrome

Background: Primary Sjogren’s syndrome (SS) is an autoimmune disease with a strong predilection for lymphoma development, with earlier disease onset being postulated as an independent risk factor for this complication. Variations of the Leukocyte immunoglobulin-like receptor A3(LILRA3) gene have been previously shown to increase susceptibility for both SS and non-Hodgkin B-cell lymphoma (B-NHL) in the general population. We aimed to investigate whether variations of the LILRA3 gene could predispose for lymphoma development in the context of SS. Methods: Study population, all of Greek origin, included 101 SS cases with a current or previous diagnosis of lymphoma (SS-lymphoma, SS-L) and 301 primary SS patients not complicated by lymphoma (SS-non-lymphoma, SS-nL). All SS patients fulfilled the 2016 SS American College of Rheumatology/European league against Rheumatism (ACR/EULAR) classification criteria. A total of 381 healthy controls (HC) of similar age/sex/race distribution were also included. On the basis of the age of SS onset and the presence or absence of adverse predictors for lymphoma development, SS patients were further stratified into younger (≤40 years) and older (>40 years) age of disease onset, as well as into high/medium and low risk groups. Polymerase chain reaction (PCR) was implemented for the detection of the following LILRA3 gene variants: homozygous non-deleted or functional wild type (+/+) heterozygous (+/−) and homozygous deleted (−/−). LILRA3 serum protein levels were quantitated by enzyme-linked immunosorbent assay (ELISA) in 85 individuals (29 SS-L, 35 SS-nL patients and 21 HC). Results: While no statistically significant differences were detected in the overall frequency of LILRA3 gene variants between SS-L, SS-nL and HC groups, LILRA3 serum protein levels were increased in the SS-L group compared to HC (1.27 ± 1.34 vs. 0.38 ± 0.34 ng/mL, p-value: 0.004). After stratification according to the age of SS onset and history of lymphoma, as well as the presence or absence of adverse predictors for lymphoma development, the prevalence of the functional LILRA3 gene variant was found to be significantly increased in the young onset SS-L group compared to the HC of similar age and sex distribution (100% vs. 82.9%, p = 0.03), as well as in the high/medium risk SS compared to the low risk SS (91.3 vs. 78.3%, p = 0.0012). Of note, young onset SS-L and SS-nL groups displayed higher LILRA3 serum levels compared to their older counterparts (p-values: 0.007 and 0.0005, respectively). Conclusion: The functional LILRA3 gene variant increases susceptibility to SS-related lymphoma development in patients with a disease onset of <40 years old, implying that genetically determined deranged immune responses in younger SS individuals could underly their pronounced risk for lymphoma development.

Leukocyte immunoglobulin-like receptor A3 is increased in IBD patients and functions as an anti-inflammatory modulator

Growing evidence shows that a homozygous 6·7-kb deletion of the novel anti-inflammatory molecule leukocyte immunoglobulin-like receptor A3 (LILRA3) is associated with many autoimmune disorders. However, its effects on pathogenesis of inflammatory bowel disease (IBD) have yet not been clarified. LILRA3 is mainly expressed in monocytes, whereas its effects on biological behaviors of monocytes have not been systematically reported. In our study, to investigate the association between LILRA3 polymorphism and IBD susceptibility, LILRA3 polymorphism was assessed in 378 IBD patients and 509 healthy controls. Quantitative real time PCR (qRT-PCR), Western blot and immunohistochemistry (IHC) were employed to detect the LILRA3 expression in IBD patient blood and intestinal samples. The human U937 monocyte cell line was employed to establish LILRA3 over-expressing cells and the effects of LILRA3 on the biological behaviors of U937 cells were systematically explored. Although no association of the polymorphism with IBD development was found, LILRA3 expression was markedly increased in IBD patients compared with healthy controls. Over-expression of LILRA3 in monocytes led to significant decreases in secretion of interferon (IFN)-γ, tumor necrosis factor (TNF)-α and interleukin (IL)-6. Additionally, LILRA3 abated monocyte migration by reducing the expression of several chemokines and enhanced monocyte phagocytosis by increasing CD36 expression. Furthermore, LILRA3 promoted monocyte proliferation through a combination of Akt and extracellular receptor kinase/mitogen-activated protein kinase (Erk/MEK) signaling pathways. We report for the first time, to our knowledge, that LILRA3 is related to IBD and functions as an anti-inflammatory modulator in U937 cells.

The genetics of Takayasu arteritis

Takayasu arteritis (TAK) is a rare systemic vasculitis that is characterized by granulomatous inflammation of the aorta and its major branches. The cellular and biochemical processes involved in the pathogenesis of TAK are beginning to be elucidated, and implicate both cell and antibody-mediated autoimmune mechanisms. In addition, the underlying etiology to TAK may be explained, at least in part, by a complex genetic contribution. The most well-recognized genetic susceptibility locus for the disease is the classical HLA allele, HLA-B*52, which has been confirmed in several ethnicities. The genetic susceptibility with HLA-B*52, as well as additional classical alleles and loci, implicate both HLA class I and class II involvement in TAK. Furthermore, genetic associations with genes encoding immune response regulators, pro-inflammatory cytokines and mediators of humoral immunity may directly relate to disease mechanisms. Non-HLA susceptibility loci that have been recently established for TAK with a genome-wide level of significance include FCGR2A/FCGR3A, IL12B, IL6, RPS9/LILRB3, and a locus on chromosome 21 near PSMG1. In this review, we present the complex genetic predisposition to TAK and discuss how recent findings identified potential targets in the pathogenesis and treatment of the disease.

LILRA3 deletion is a genetic risk factor of HIV infection

OBJECTIVE

The aim of this study is to analyse the influence of LILRA3 and the genetic leukocyte immunoglobulin-like receptor 3 (LILRA3) deletion on transmission and clinical course of HIV infection.

DESIGN

Case and control study.

METHODS

LILRA3 genotypes were determined by PCR. HIV patients were categorized into short-term progressors, normal progressors and long-term nonprogressors according to the clinical course. Functional studies were performed using real-time PCR, intracellular flow cytometry and ELISA.

RESULTS

The prevalence of the homozygous LILRA3 deletion was higher in HIV-positive individuals (n = 439) than in controls (n = 651) (P = 0.02). The disease progression was faster in homozygously deleted patients with more short-term progressors than in heterozygous (P = 0.03) and homozygously positive (P = 0.002) individuals. These results have been confirmed in a seroconverter cohort (n = 288). The frequency of the homozygous deletion in the confirmation cohort was higher than in controls (P = 0.04). Combining both cohorts, the proportion of homozygously LILRA3-deleted individuals was 6.2% in HIV-infected patients (n = 727) vs. 3.2% in controls (P = 0.01). Functional analysis revealed an upregulation of the LILRA3 gene in real-time PCR in treated patients when compared with untreated patients (P = 0.007) and controls (P = 0.02) resulting in a higher LILRA3 expression in CD4 (P = 0.008) and CD14 (P = 0.02) cells of untreated patients in intracellular flow cytometry. LILRA 3 concentrations in the sera were similar between the groups, in untreated patients a correlation between viral load and LILRA3 concentration was found.

CONCLUSION

The homozygous LILRA3 deletion is associated with a higher susceptibility for HIV disease and with a faster disease progression.

TLR8 regulation of LILRA3 in monocytes is abrogated in human immunodeficiency virus infection and correlates to CD4 counts and virus loads

BACKGROUND

LILRA3 is an immunostimulatory molecule which can conditionally induce the proliferation of cytotoxic cells. LILRA3 has a deletion genotype which is associated with multiple immune disorders. In this study, we wanted to analyze the regulation of LILRA3 and its significance in the context of HIV infection.

RESULTS

We analyzed a panel of TLR agonists and found that ssRNA40, a TLR8 agonist, is a potent inducer of LILRA3 in healthy individuals. However, this regulation is much diminished in HIV. Comparison of TLR8 to TLR4 induction of LILRA3 indicated that LPS induces less LILRA3 than ssRNA40 among healthy controls, but not HIV patients. Levels of LILRA3 induction correlated to virus load and CD4 counts in untreated patients. Recombinant LILRA3 can induce a host of proinflammatory genes which include IL-6 and IL-1α, as well as alter the expression of MHC and costimulatory molecules in monocytes and B-cells.

CONCLUSION

Our experiments point towards a beneficial role for LILRA3 in virus infections, especially in ssRNA viruses, like HIV, that engage TLR8. However, the potentially beneficial role of LILRA3 is abrogated during a HIV infection. We believe that more work has to be done to study the role of LILRA3 in infectious diseases and that there is a potential for exploring the use of LILRA3 in the treatment of virus infections.