Clinicopathologic features of relapsed CD19(-) B-ALL in CD19-targeted immunotherapy: Biological insights into relapse and LILRB1 as a novel B-cell marker for CD19(-) B lymphoblasts

INTRODUCTION

The mechanism of relapsed CD19(-) B-ALL after anti-CD19 immunotherapy (Kymriah [CART-19] and blinatumomab) is under active investigation. Our study aims to assess LILRB1 as a novel B-cell marker for detecting CD19(-) B-lymphoblasts and to analyze the clinicopathologic/genetic features of such disease to provide biological insight into relapse.

METHODS

Six patients (3 males/3 females, median age of 14 years) with relapsed CD19(-) B-ALL were analyzed for cytogenetic/genetic profile and immunophenotype.

RESULTS

CD19(-) B-ALL emerged after an interval of 5.8 months following anti-CD19 therapy. Five of six patients had B-cell aplasia, indicative of a persistent effect of CART or blinatumomab at relapse. Importantly, LILRB1 was variably expressed on CD19(-) and CD19(+) B lymphoblasts, strong on CD34(+) lymphoblasts and dim/partial on CD34(-) lymphoblasts. Three of six patients with paired B-ALL samples (pre- and post-anti-CD19 therapy) carried complex and different cytogenetic abnormalities, either as completely different or sharing a subset of cytogenetic abnormalities.

CONCLUSION

LILRB1 can be used as a novel B-cell marker to identify CD19(-) B lymphoblasts. The emergence of CD19(-) B-ALL appears to be associated with complex cytogenetic evolutions. The mechanism of CD19(-) B-ALL relapse under anti-CD19 immune pressure remains to be explored by comprehensive molecular studies.

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.

Overall avidity declines in TCR repertoires during latent CMV but not EBV infection

Introduction

The avidity of the T-cell receptor (TCR) for antigenic peptides presented by the MHC (pMHC) on cells is an essential parameter for efficient T cell-mediated immunity. Yet, whether the TCR-ligand avidity can drive the clonal evolution of virus antigen-specific CD8 T cells, and how this process is determined in latent Cytomegalovirus (CMV)- against Epstein-Barr virus (EBV)-mediated infection remains largely unknown.

Methods

To address these issues, we quantified monomeric TCR-pMHC dissociation rates on CMV- and EBV-specific individual TCRαβ clonotypes and polyclonal CD8 T cell populations in healthy donors over a follow-up time of 15-18 years. The parameters involved during the long-term persistence of virus-specific T cell clonotypes were further evaluated by gene expression profiling, phenotype and functional analyses.

Results

Within CMV/pp65-specific T cell repertoires, a progressive contraction of clonotypes with high TCR-pMHC avidity and low CD8 binding dependency was observed, leading to an overall avidity decline during long-term antigen exposure. We identified a unique transcriptional signature preferentially expressed by high-avidity CMV/pp65-specific T cell clonotypes, including the inhibitory receptor LILRB1. Interestingly, T cell clonotypes of high-avidity showed higher LILRB1 expression than the low-avidity ones and LILRB1 blockade moderately increased T cell proliferation. Similar findings were made for CD8 T cell repertoires specific for the CMV/IE-1 epitope. There was a gradual in vivo loss of high-avidity T cells with time for both CMV specificities, corresponding to virus-specific CD8 T cells expressing enhanced LILRB1 levels. In sharp contrast, the EBV/BMFL1-specific T cell clonal composition and distribution, once established, displayed an exceptional stability, unrelated to TCR-pMHC binding avidity or LILRB1 expression.

Conclusions

These findings reveal an overall long-term avidity decline of CMV- but not EBV-specific T cell clonal repertoires, highlighting the differing role played by TCR-ligand avidity over the course of these two latent herpesvirus infections. Our data further suggest that the inhibitor receptor LILRB1 potentially restricts the clonal expansion of high-avidity CMV-specific T cell clonotypes during latent infection. We propose that the mechanisms regulating the long-term outcome of CMV- and EBV-specific memory CD8 T cell clonotypes in humans are distinct.

HLA-F and LILRB1 Genetic Polymorphisms Associated with Alloimmunisation in Sickle Cell Disease

Red blood cell (RBC) transfusion remains a critical component in caring for the acute and chronic complications of sickle cell disease (SCD). Patient alloimmunisation is the main limitation of transfusion, which can worsen anaemia and lead to delayed haemolytic transfusion reaction or transfusion deadlock. Although biological risk factors have been identified for immunisation, patient alloimmunisation remains difficult to predict. We aimed to characterise genetic alloimmunisation factors to optimise the management of blood products compatible with extended antigen matching to ensure the self-sufficiency of labile blood products. Considering alloimmunisation in other clinical settings, like pregnancy and transplantation, many studies have shown that HLA Ib molecules (HLA-G, -E, and -F) are involved in tolerance mechanism; these molecules are ligands of immune effector cell receptors (LILRB1, LILRB2, and KIR3DS1). Genetic polymorphisms of these ligands and receptors have been linked to their expression levels and their influence on inflammatory and immune response modulation. Our hypothesis was that polymorphisms of HLA Ib genes and of their receptors are associated with alloimmunisation susceptibility in SCD patients. The alloimmunisation profile of thirty-seven adult SCD patients was analysed according to these genetic polymorphisms and transfusion history. Our results suggest that the alloimmunisation of SCD patients is linked to both HLA-F and LILRB1 genetic polymorphisms located in their regulatory region and associated with their protein expression level.

LILRB receptor-mediated regulation of myeloid cell maturation and function

The leukocyte immunoglobulin-like receptor (LILR) family comprises a set of paired immunomodulatory receptors expressed among human myeloid and lymphocyte cell populations. While six members of LILR subfamily A (LILRA) associate with membrane adaptors to signal via immunoreceptor tyrosine-based activating motifs (ITAM), LILR subfamily B (LILRB) members signal via multiple cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIM). Ligand specificity of some LILR family members has been studied in detail, but new perspective into the immunoregulatory aspects of this receptor family in human myeloid cells has been limited. LILRB receptors and the murine ortholog, paired immunoglobulin-like receptor B (PIRB), have been shown to negatively regulate maturation pathways in myeloid cells including mast cells, neutrophils, dendritic cells, as well as B cells. Our laboratory further demonstrated in mouse models that PIRB regulated functional development of myeloid-derived suppressor cell and the formation of a tumor-permissive microenvironment. Based on observations from the literature and our own studies, our laboratory is focusing on how LILRs modulate immune homeostasis of human myeloid cells and how these pathways may be targeted in disease states. Integrity of this pathway in tumor microenvironments, for example, permits a myeloid phenotype that suppresses antitumor adaptive immunity. This review presents the evidence supporting a role of LILRs as myeloid cell regulators and ongoing efforts to understand the functional immunology surrounding this family.

Possible Role of HLA-G, LILRB1 and KIR2DL4 Gene Polymorphisms in Spontaneous Miscarriage

The KIR2DL4 receptor and its ligand HLA-G are considered important for fetal-maternal immune tolerance and successful pregnancy. The absence of a particular variant of KIR2DL4 might be a bad prognostic factor for pregnancy outcome. However, it could be compensated by the presence of the respective LILRB1 allele. Therefore, we investigated the KIR2DL4, LILRB1 and HLA-G polymorphisms in 277 couples with spontaneous abortion and 219 control couples by HRM, PCR-SSP and RFLP methods. We found a protective effect of women’s heterozygosity in −716 HLA-G (p = 0.0206) and LILRB1 (p = 0.0131) against spontaneous abortion. Surprisingly, we observed more 9A/10A genotypes of KIR2DL4 gene carriers in the group of male partners from the miscarriage group in comparison to the men from the control group (p = 0.0288). Furthermore, there was no association of women’s KIR2DL4 polymorphism with susceptibility to spontaneous abortion. Multivariate analysis indicated that women’s −716 HLA-G and LILRB1 and men’s KIR2DL4 9A/10A are important in terms of the protection or susceptibility to miscarriage, respectively (p = 0.00968). In conclusion, a woman’s heterozygosity in HLA-G and LILRB1 might be an advantage for a success of reproduction, but the partner’s heterozygosity in 9A/10A KIR2DL4 alleles might not.

The paradox of high availability and low recognition of soluble HLA-G by LILRB1 receptor in rheumatoid arthritis patients

HLA-G is a regulatory molecule involved in immunologic tolerance. Growing evidence indicates that HLA-G plays a role in the regulation of inflammatory processes and autoimmune diseases. This study aimed at a systematic evaluation of soluble HLA-G (sHLA-G) in plasma of rheumatoid arthritis (RA) patients with long-lasting chronic inflammation. RA patients (n=68) and healthy controls (n=26) had their plasmatic sHLA-G measured by ELISA whereas the binding capability of sHLA-G to its cognate LILRB1 receptor was measured by a Luminex-based assay. All subjects were PCR-genotyped for HLA-G 14bp polymorphism (rs66554220). Significantly higher sHLA-G levels were observed in patients (p<0.001), however no significant differences were observed in LILRB1 binding capacity between RA patients and controls. Remarkably, the proportion of patients presenting specific binding of sHLA-G to LILRB1 was significantly decreased as compared to controls (56% vs. 81%, p=0.027). Patients without rheumatoid factor (RF-) were significantly overrepresented in the group of patients positive for LILRB1 binding as compared to patients without LILRB1 binding (31% vs 10%, p=0.033). Furthermore, methotrexate treated patients (n=58) revealed significantly lower LILRB1 binding to sHLA-G molecules than non-treated patients (medians: 12.2 vs. 67.7 units/ml, p=0.031). Unlike in controls, no significant differences in sHLA-G levels were observed among patients grouped by 14pb genotype. Thus, in a substantial number of late RA patients, the circulating sHLA-G molecules are impaired regarding LILRB1 recognition, meaning that although increased levels are observed; these molecules are not qualified to exert their protective functions against inflammation. Our findings offer new insights into the immunopathology of RA patients with long-lasting anti-RA-treatment and highlight the importance to also measure the binding capability of sHLA-G to LILRB1.

Soluble human leukocyte antigen-g5 activates extracellular signal-regulated protein kinase signaling and stimulates trophoblast invasion

Soluble human leukocyte antigen-G (HLA-G) is a non-classical class Ib HLA molecule that is secreted from blastocysts. Soluble HLA-G modulates the immune tolerance of the mother and can be used as a prognostic factor for the clinical pregnancy rate. However, the underlying mechanism of how soluble HLA-G5 affects pregnancy remains largely unknown. We hypothesized that soluble HLA-G5 promotes successful implantation and pregnancy by modulating trophoblast invasion through receptor binding and activation of extracellular signal-regulated protein kinase (ERK) signaling pathway. Recombinant HLA-G5 protein over-expressed in E. coli BL21 was purified to near homogeneity. We studied the expression of HLA-G5 and its receptors, the leukocyte immunoglobulin-like receptor subfamily B1 (LILRB1) and killer cell immunoglobulin-like receptor 2DL4 (KIR2DL4), in primary trophoblasts and trophoblastic (JAr and JEG-3) cell lines by florescence-labeled HLA-G5. HLA-G5 was detected in the primary trophoblasts and JEG-3 cells. The LILRB1 and KIR2DL4 receptors were expressed in both primary trophoblasts and trophoblastic cell lines. HLA-G5 stimulated cell invasion (p<0.05) and increased urokinase (uPA) and matrix metalloproteinases (MMPs) transcripts and their activity (p<0.05) in trophoblastic cells. HLA-G5 activated the ERK signaling pathway and induced ERK1/2 phosphorylation in the trophoblastic cell lines. Addition of ERK inhibitors (U0126 and PD98059) nullified the stimulatory effect of HLA-G5 on trophoblastic cell invasion. Taken together, HLA-G5 induced trophoblast invasion by binding to KIR2DL4 and LILRB1, by increasing uPA and MMPs expressions and by activating the ERK signaling pathway.

Total expression of HLA-G and TLR-9 in chronic lymphocytic leukemia patients

Suppressed immune status facilitates immune escape mechanisms that allow chronic lymphocytic leukemia cells to proliferate and expand. The expression of HLA-G could effectively inhibit the immune response. In immune response inhibitory signals follow activation of immune system which might be occur during bacterial or viral infection in CLL patients. In the current study we characterized two components of immune system, inhibitory molecule HLA-G with its receptor - CD85j and Toll-like receptor 9. The material was obtained from 41 CLL patients and 41 HV with similar median age. In CLL patients expression of intracellular and surface HLA-G and soluble HLA-G levels were significantly higher than in HV. We found higher expression of CD85j compared to HV and the positive correlation between expression of HLA-G and CD85j. All the CLL cells expressed TLR-9, and the level of expression positively correlated with expression of HLA-G and CD85j. Patients with higher expression of intracellular expression of TLR-9 have significantly longer treatment-free survival than patients with low expression of TLR-9 (57 months vs. 8 months, respectively). Summarizing in CLL we characterized activatory and inhibitory components of immune system that might be connected functionally. Analysis of TLR-9 expression might have additional prognostic value for CLL patients.

Cytokine production by non-stimulated peripheral blood NK cells and lymphocytes in early-onset severe pre-eclampsia without HELLP

Preeclampsia involves an exacerbated maternal inflammatory response that suggests a possible role of innate immunity. NK cells can promote this kind of response through cytokine production and the expression of activating or inhibitory receptors. The aims of the present study were to explore cytokine production by peripheral blood mononuclear cells, as well as cytotoxic ability and receptor expression for HLA-E and HLA-G molecules in peripheral natural killer (NK) cells of women with early-onset severe preeclampsia without HELLP (hemolysis, elevated liver enzyme levels and a low platelet count) syndrome. The expression of the ILT2, KIRDL4, NKG2A, and NKG2C receptors and of cytotoxic activity was measured in non-stimulated NK cells, whereas the intracellular expression of IL-4, IL-10, IL-13, IL-12, IFNγ, TNF and VEGF, was assessed in non-stimulated peripheral blood mononuclear cells subsets using flow cytometry. Circulating soluble HLA-G was also determined by ELISA. The intracellular cytokines tested were significantly higher in NK cell subsets from severely preeclamptic women compared with the control group. On the other hand, the percentage of NK cells expressing NKG2A or NKG2C and the cytotoxic activity of NK cells were significantly higher in severely preeclamptic women. Furthermore, there was a significant correlation between urine protein concentration and soluble human leukocyte antigen G (soluble HLA-G) in serum. We conclude that patients with early-onset severe preeclampsia without HELLP syndrome have increased NK cell function related to cytokine production, cytotoxicity and expression of lectin-like receptors such as NKG2.

HLA-G may predict the disease course in patients with early rheumatoid arthritis

The current management of early rheumatoid arthritis (ERA) is to start an intensive treatment as soon as possible. To avoid under/overtreatment, it is important to identify reliable ERA evolution biomarkers. HLA-G molecules has been associated with rheumatoid arthritis, suggesting a role in disease regulation. HLA-G antigens are expressed as membrane bound and soluble isoforms (mHLA-G, sHLA-G) that act as ligand for immune-inhibitory receptors (ILT2, ILT4, KIR2DL4). Expression of HLA-G is influenced by a 14 bp insertion/deletion polymorphism in exon 8 of the gene, where the deletion is associated with mRNA stability. We analyzed 23 ERA patients during a 12 months follow-up disease treatment for sHLA-G, IL-1beta, IL-6, IL-10 and TNF-alpha levels in plasma samples by ELISA, mHLA-G and ILT2 expression on peripheral blood CD14 positive cells by flow cytometry and typed HLA-G 14 bp deletion/insertion polymorphism by Real-Time PCR. Disease status (DAS28), ultrasonography with power Doppler and laboratory data were checked. Cytokine levels confirmed the anti-inflammatory effect of the treatment. sHLA-G, mHLA-G and ILT2 expression inversely correlated with DAS28 disease scores. The frequency of 14 bp deletion allele increased in patients with disease remission. Based on these results, HLA-G may be a candidate biomarker to evaluate early prognosis and disease activity in ERA patients.

MiRNA-mediated control of HLA-G expression and function

HLA-G is a non-classical HLA class-Ib molecule expressed mainly by the extravillous cytotrophoblasts (EVT) of the placenta. The expression of HLA-G on these fetal cells protects the EVT cells from immune rejection and is therefore important for a healthy pregnancy. The mechanisms controlling HLA-G expression are largely unknown. Here we demonstrate that miR-148a and miR-152 down-regulate HLA-G expression by binding its 3'UTR and that this down-regulation of HLA-G affects LILRB1 recognition and consequently, abolishes the LILRB1-mediated inhibition of NK cell killing. We further demonstrate that the C/G polymorphism at position +3142 of HLA-G 3'UTR has no effect on the miRNA targeting of HLA-G. We show that in the placenta both miR-148a and miR-152 miRNAs are expressed at relatively low levels, compared to other healthy tissues, and that the mRNA levels of HLA-G are particularly high and we therefore suggest that this might enable the tissue specific expression of HLA-G.

Analysis of expression and function of the inhibitory receptor ILT2 in lymphocytes from patients with autoimmune thyroid disease

OBJECTIVE

Autoimmune thyroid disease (AITD) is characterized by different defects in immunoregulatory mechanisms. The immunoglobulin-like transcript receptor 2 (ILT2) or leukocyte Ig-like receptor 1 (LIRB1/CD85j) exerts an important immunoregulatory role. We hypothesized that the lymphocytes from AITD patients have a diminished expression and function of ILT2. The aim of this study was to investigate the expression and function of ILT2 in lymphocytes from patients with AITD.

DESIGN AND METHODS

In this study, 18 patients with Hashimoto's thyroiditis (HT), 20 with Graves' disease, and 26 healthy controls were studied. ILT2 expression was analyzed by flow cytometry and immunohistochemistry in peripheral blood mononuclear cells (PBMC) and thyroid tissue. The regulatory function of ILT2 was assessed by an assay of inhibition of lymphocyte proliferation and by an analysis of cell cycle progression. The effect of ILT2 on cytokine synthesis was also evaluated.

RESULTS

We found a significant increased expression of ILT2 by lymphocytes in AITD patients. ILT2 was also detected in the leukocyte infiltrate of thyroid tissue from HT patients. On the contrary, a significant diminished inhibitory activity of ILT2 on cell proliferation was observed in AITD patients. In addition, PBMC from AITD patients showed a diminished synthesis of interleukin 10 on ILT2 engagement.

CONCLUSIONS

The abnormal expression and function of ILT2 detected in AITD suggests that this receptor may participate in the pathogenesis of this condition.

HLA-G and HLA-E in patients with juvenile idiopathic arthritis

OBJECTIVE

To investigate the expression and release of HLA-G and HLA-E in JIA.

METHODS

Soluble (s)HLA-G and HLA-E were measured in sera from 58 JIA patients and 54 healthy donors. Surface expression of HLA-G, HLA-E and immunoglobulin-like transcript (ILT)2 and ILT4, two receptors for HLA-G, was assessed on T, B cells and monocytes from peripheral blood (PB) and SF of 12 JIA patients and from PB of 12 controls.

RESULTS

Serum sHLA-G concentration was significantly lower in patients than in controls. Both sHLA-G and sHLA-E were detected in SF and sHLA-E concentration in SF was higher in extended oligoarticular/polyarticular than in limited oligoarticular JIA. Patients compared with controls showed: (i) down-regulation of HLA-E and ILT2 expression on T cells; (ii) up-regulation of HLA-E expression on B cells and monocytes; and (iii) down-regulation of ILT4 expression on monocytes. Comparing JIA patients' SF and PB we found: (i) up-regulation of HLA-E and ILT2 expression in T and B cells and monocytes; and (ii) down-regulation of ILT4 expression in monocytes. ILT4 was up-regulated in monocytes from oligoarticular extended/polyarticular compared with oligoarticular limited JIA.

CONCLUSIONS

A lower concentration of sHLA-G in sera may predispose to JIA, as observed for other autoimmune diseases. sHLA-E concentration in SF correlate with the number of affected joints. Higher ILT2 expression on SF cell populations compared with PB may be related to high sHLA-G concentration in SF. Higher HLA-E expression in SF than in PB cell populations may protect them from NK cytolysis.

LILRA3 binds both classical and non-classical HLA class I molecules but with reduced affinities compared to LILRB1/LILRB2: structural evidence

Structurally, Group 1 LILR (Leukocyte Immunogloblin (Ig)-Like Receptor, also known as Ig-like transcripts, ILT; Leukocyte Ig-like receptor, LIR; and CD85) members are very similar in terms of the HLAIs (human leukocyte antigen class I molecules) binding region and were hypothesized that they all bind to HLAIs. As one of the Group 1 LILRs, LILRA3 is the only secretory LILR and may greatly control the inhibitory immune response induced by LILRB1, LILRB2, and other HLA-binding LILR molecules like LILRA1. Nevertheless, little was known about the binding of LILRA3 to HLAIs. In this report, we present the crystal structure of the LILRA3 domain 1 (D1) and evaluate the D1 and D1D2 (domain 1 and domain 2) binding to classical and non-classical HLAIs using BIAcore® surface plasmon resonance analysis (SPR). We found that LILRA3 binds both classical HLA-A*0201 and non-classical HLA-G1 but with reduced affinities compared to either LILRB1 or LILRB2. The polymorphic amino acids and the LILRA3 D1 structure support this notion.

[Applications of monitoring human leukocyte antigen G and its inhibitory receptors in post-renal transplantation]

OBJECTIVE

to study the feasibility of human leucocyte antigen-G (HLA-G) as a post-transplantation prognostic biomarker and discuss the correlation of its receptor expression and the mechanisms.

METHODS

a total of 215 recipients in our centre from February 2006 to June 2008 were divided into stable kidney function group (n = 173) and acute rejection group (n = 42). The soluble human leucocyte antigen-G5 (sHLA-G5) level in peripheral plasma was detected by ELISA. And the HLA-G receptor ILT-2, KIR2DL4 on T, B, NK lymphocytes were analyzed by flow cytometry (FCM). The sHLA-G5 cutoff level by ROC curve was employed to predict the events of acute post-transplantation rejection. And regression analysis was used to determine the association of sHLA-G5 with acute rejection.

RESULTS

an optimal cutoff value of 139.0 microg/L could be defined for sHLA-G5 (sensitivity: 63.6%, specificity: 82.1%, AUC: 0.780). Binary regression analysis showed that sHLA-G5 played an independent role on acute rejection (P = 0.019, OR = 0.039, 95%CI: 2.091 - 5.661). The rate of HLA-G receptor ILT-2 on CD4(+)T cell, CD8(+)T cell and B cell in acute rejection group was statistically lower than that in stable kidney function group (21% ± 7% vs 52% ± 17%, 23% ± 6% vs 39% ± 16%, 21% ± 7% vs 39% ± 16%, all P < 0.05). The expression of KIR2DL4 on NK cells in acute rejection group was statistically lower than that in stable kidney function group (31% ± 10%vs 57% ± 21%, P < 0.05).

CONCLUSION

sHLA-G5 level may be predicted for acute rejection with a high sensitivity and specificity. The up-regulated expression of ILT-2 and KIR2DLT may contribute to immunology tolerance in peripheral circulation.

Natural killer cell killing of acute myelogenous leukemia and acute lymphoblastic leukemia blasts by killer cell immunoglobulin-like receptor-negative natural killer cells after NKG2A and LIR-1 blockade

Although the study of natural killer (NK) cell alloreactivity has been dominated by studies of killer cell immunoglobulin-like receptors (KIRs), we hypothesized that NKG2A and LIR-1, present on 53% +/- 13% and 36% +/- 18% of normal NK cells, respectively, play roles in the NK cell killing of primary leukemia targets. KIR(-) cells, which compose nearly half of the circulating NK cell population, exhibit tolerance to primary leukemia targets, suggesting signaling through other inhibitory receptors. Both acute myelogenous leukemia and acute lymphoblastic leukemia targets were rendered susceptible to lysis by fresh resting KIR(-) NK cells when inhibitory receptor-major histocompatibility class I interactions were blocked by pan-HLA antibodies, demonstrating that these cells are functionally competent. Blockade of a single inhibitory receptor resulted in slightly increased killing, whereas combined LIR-1 and NKG2A blockade consistently resulted in increased NK cell cytotoxicity. Dual blockade of NKG2A and LIR-1 led to significant killing of targets by resting KIR(-) NK cells, demonstrating that this population is not hyporesponsive. Together these results suggest that alloreactivity of a significant fraction of KIR(-) NK cells is mediated by NKG2A and LIR-1. Thus strategies to interrupt NKG2A and LIR-1 in combination with anti-KIR blockade hold promise for exploiting NK cell therapy in acute leukemias.

[Expressions of CD1a and CD83 of Langerhans cells in the local lesions of epidermodysplasia verruciformis patients]

OBJECTIVE

To investigate the expressions of CD1a and CD83 of Langerhans cells (LC) in the lesions of epidermodysplasia verruciformis (EV) patients.

METHODS

We used immunohistochemical method to detect the expressions of CD1a and CD83 in the lesions of 10 patients with EV lesions and in the skins of 10 normal subjects.

RESULTS

No CD83 + LCs was detected in all EV patients and normal controls, but CD1a + LC was found in all cases. The quantity of CD1a + LCs in the lesions of EV patients was significantly lower than that in the normal skin (P < 0.01); furthermore, the distribution of LCs in EV lesions was uneven.

CONCLUSION

The functions of LCs may be inhibited in EV patients.

NADPH oxidase and uncoupled nitric oxide synthase are major sources of reactive oxygen species in oral squamous cell carcinoma. Potential implications for immune regulation in high oxidative stress conditions

The development of cancer is associated with high oxidative stress and at the same time with immune system activation. Tumors develop efficient mechanisms of protection against the immune response, which allow them to escape the immune surveillance. Simultaneously, key events in the process of carcinogenesis are related to oxidative stress. The relationship between the two remains unknown. Novel understanding of oxidative stress shows that discrete changes of activities of certain enzyme systems such as NADPH oxidases or nitric oxide synthases may be more important than the overall balance of production and removal of reactive oxygen species. Such imbalance of nitric oxide and superoxide production could modify inflammation and immune regulation. We studied superoxide anion production (by lucigenin enhanced chemiluminescence - 5 microM), NADPH oxidase activity and nitric oxide synthase (NOS) dysfunction. In parallel mRNA expression of immunomodulatory markers such as FoxP3 (T regulatory cell marker), CCR6 (mucosal homing effector T cell marker) and CD85j (NK cell/CD8 T cell Ig-like MHC class I inhibitory receptor) was determined. Basal superoxide production and NADPH oxidase activity are increased in oral squamous cell carcinoma. Tumor superoxide production was inhibited by NADPH oxidase inhibitor apocynin and by NOS inhibitor L-NAME. This indicates, for the first time, that oral squamous cell carcinoma is characterized by dysregulated nitric oxide synthase, which apart from increased NADPH oxidase activity contributes to oxidative stress and may be related to the immuno-pathology of these tumors. Studied tumors were infiltrated by CCR6+, but showed lower expression of both CD85j and FoxP3 mRNA. Finally, the CD85j mRNA expression was inversely correlated to oxidative stress parameters. These preliminary studies indicate that tumor oxidative stress, related to NADPH oxidase activity and NOS activity could be related to immune responses to cancer, thus therapeutic modification of oxidative stress, which could include the correction of NOS dysfunction, could facilitate immune surveillance.

A homodimeric complex of HLA-G on normal trophoblast cells modulates antigen-presenting cells via LILRB1

In healthy individuals, the non-classical MHC molecule HLA-G is only expressed on fetal trophoblast cells that invade the decidua during placentation. We show that a significant proportion of HLA-G at the surface of normal human trophoblast cells is present as a disulphide-linked homodimer of the conventional beta(2)m-associated HLA-I complex. HLA-G is a ligand for leukocyte immunoglobulin-like receptors (LILR), which bind much more efficiently to dimeric HLA-G than to conventional HLA-I molecules. We find that a LILRB1-Fc fusion protein preferentially binds the dimeric form of HLA-G on trophoblast cells. We detect LILRB1 expression on decidual myelomonocytic cells; therefore, trophoblast HLA-G may modulate the function of these cells. Co-culture with HLA-G(+) cells does not inhibit monocyte-derived dendritic cell up-regulation of HLA-DR and costimulatory molecules on maturation, but did increase production of IL-6 and IL-10. Furthermore, proliferation of allogeneic lymphocytes was inhibited by HLA-G binding to LILRB1/2 on responding antigen-presenting cells (APC). As HLA-G is the only HLA-I molecule that forms beta(2)m-associated dimers with increased avidity for LILRB1, this interaction could represent a placental-specific signal to decidual APC. We suggest that the placenta is modulating maternal immune responses locally in the uterus through HLA-G, a trophoblast-specific, monomorphic signal present in almost every pregnancy. See accompanying commentary: (http://dx.doi.org/10.1002/eji.200737515).

Analysis of expression and function of the inhibitory receptor ILT2 (CD85j/LILRB1/LIR-1) in peripheral blood mononuclear cells from patients with systemic lupus erythematosus (SLE)

The aim of this work was to study the expression and function of the inhibitory receptor ILT2/CD85j in peripheral blood mononuclear cells (PBMC) from patients with systemic lupus erythematosus (SLE). We studied 23 SLE patients as well as 17 patients with rheumatoid arthritis, 10 with fibromyalgia, and 23 healthy individuals. We found a variable level of expression of ILT2 in the PBMC from both SLE patients and controls, with no significant differences among them. However, when the expression of this receptor was assessed in cell subsets, significantly lower levels were detected in CD19+ lymphocytes from SLE patients compared with healthy controls. Functional assays performed in unfractionated PBMC, showed a significant diminished inhibitory activity of ILT2 in CD4+ and CD8+ cell subsets from SLE patients compared to either rheumatoid arthritis or fibromyalgia patients, and healthy individuals. Our results show that the PBMC from some patients with SLE show a defective expression of ILT2, and that most of them exhibit a poor function of this inhibitory receptor.

Nonleukoreduced red blood cell transfusion induces a sustained inhibition of neutrophil chemotaxis by stimulating in vivo production of transforming growth factor-beta1 by neutrophils: role of the immunoglobulinlike transcript 1, sFasL, and sHLA-I

BACKGROUND

Red blood cell (RBC) transfusion has been linked to increased susceptibility to infections in critically ill patients and to augmented incidence of postoperative infections. The mechanisms by which transfusions can induce immunosuppression are only partially defined. Recently, it has been demonstrated that RBC supernatants inhibit neutrophil migration. Such inhibitory activity is due to transforming growth factor (TGF)-beta1 contained in the supernatants that desensitize neutrophils to subsequent chemotaxic stimulation.

STUDY DESIGN AND METHODS

In ancillary experiments, it was observed that plasma from transfused patients maintained its capacity of inhibiting neutrophil chemotaxis several days after RBC transfusion. Thus, this study was planned to investigate the mechanism(s) responsible for the prolonged inhibition of neutrophil chemotaxis observed after RBC transfusion.

RESULTS

Plasma samples obtained from subjects who underwent RBC transfusion display a capability of inhibiting neutrophil chemotaxis, which is detectable up to 15 days after the transfusion. The inhibition is related to the capacity of FasL and HLA-I molecules contained in RBC supernatants to induce in vivo TGF-beta1 synthesis by neutrophils. The induction of TGF-beta1 secretion in neutrophils by HLA-I molecules depends on immunoglobulinlike transcript 1/CD85 triggering.

CONCLUSION

The property of RBC transfusion of inducing a sustained inhibition of neutrophil chemotaxis seems to be a potential mechanism that concurs to the susceptibility to infections in patients who receive transfusions. Furthermore, our findings, showing neutrophil production of TGF-beta1 in response to FasL and HLA-I molecules, confirm that neutrophils are endowed not only with effector functions but also with immunomodulatory properties possibly involved in the regulation of inflammatory processes.

The human cytomegalovirus MHC class I homolog UL18 inhibits LIR-1+ but activates LIR-1- NK cells

The inhibitory leukocyte Ig-like receptor 1 (LIR-1, also known as ILT2, CD85j, or LILRB1) was identified by its high affinity for the human CMV (HCMV) MHC class I homolog gpUL18. The role of this LIR-1-gpUL18 interaction in modulating NK recognition during HCMV infection has previously not been clearly defined. In this study, LIR-1(+) NKL cell-mediated cytotoxicity was shown to be inhibited by transduction of targets with a replication-deficient adenovirus vector encoding UL18 (RAd-UL18). Fibroblasts infected with an HCMV UL18 mutant (DeltaUL18) also exhibited enhanced susceptibility to NKL killing relative to cells infected with the parental virus. In additional cytolysis assays, UL18-mediated protection was also evident in the context of adenovirus vector transduction and HCMV infection of autologous fibroblast targets using IFN-alpha-activated NK bulk cultures derived from a donor with a high frequency of LIR-1(+) NK cells. A single LIR-1(high) NK clone derived from this donor was inhibited by UL18, while 3 of 24 clones were activated. CD107 mobilization assays revealed that LIR-1(+) NK cells were consistently inhibited by UL18 in all tested donors, but this effect was often masked in the global response by UL18-mediated activation of a subset of LIR-1(-) NK cells. Although Ab-blocking experiments support UL18 inhibition being induced by a direct interaction with LIR-1, the UL18-mediated activation is LIR-1 independent.

Soluble HLA-G and HLA-G1 Expressing Antigen-Presenting Cells Inhibit T-Cell Alloproliferation through ILT-2/ILT-4/FasL-Mediated Pathways

HLA-G is a tolerogenic molecule involved in maternal-fetal tolerance and in allograft acceptance. Soluble HLA-G proteins are present at high levels in plasma from transplanted patients who better accept their graft. In addition, infiltrating mononuclear cells expressing HLA-G can be detected within grafted tissues. To define the role of these HLA-G proteins in preventing graft rejection, we investigated the ability of HLA-G1 expressing antigen presenting cells (APC) and of soluble HLA-G proteins (i.e., HLA-G5 and shed HLA-G1) to inhibit T-cell alloproliferation and analyzed the molecules involved in such inhibition. Results demonstrated that both membrane-bound and soluble HLA-G proteins inhibited T-cell alloproliferation. This inhibition involved engagement of immunoglobulinlike transcript (ILT)-2 and ILT-4 receptors by HLA-G. Moreover, blocking Fas ligand (FasL) reversed HLA-G mediated inhibition, demonstrating that the Fas/FasL pathway is also recruited by HLA-G to exert its immunosuppressive function on T cells. These data highlight the role played by HLA-G in better graft acceptance status observed in transplanted patients with HLA-G(+) grafted cells and high HLA-G plasma levels. Evidence to support such role in vivo was provided by the capacity of purified HLA-G5 from the plasma of the transplanted patient to suppress T-cell alloresponses.

Detection of weak ligand interactions of leukocyte Ig-like receptor B1 by fluorescence correlation spectroscopy

Fluorescence correlation spectroscopy (FCS) can directly and quickly detect the translational diffusion of individual fluorescence-labeled molecules in solutions. Although FCS analyses for protein-protein interactions have been performed, the very weak interactions generally observed in cell-cell recognition of the immune system have not been examined in detail. Here, we report the FCS analysis for low-affinity and fast-kinetic binding (K(d) greater than muM range) of the human inhibitory immune cell surface receptor, leukocyte immunoglobulin-like receptor B1 (LILRB1), to its ligands, MHC (major histocompatibility complex) class I molecules (MHCIs) by using the single-molecule FCS detection system which requires only a small amount of sample. Since the random labeling technique for LILRB1 disturbed the MHCI binding, we performed site-specific labeling of LILRB1 by introducing a cysteine residue at the C-terminus, which could be covalently attached with the fluorescence reagent, Alexa647. This technique can be applied to other type I membrane receptors. The low-affinity binding of LILRB1-Alexa647 to MHCIs (HLA-Cw4, and -G1) was detected by FCS, even though non-labeled MHCIs were only twice as big as the labeled LILRB1. Their dissociation constants (7.5 muM (HLA-Cw4) and 5.7 muM (HLA-G1)) could be determined and were consistent with surface plasmon resonance (SPR) data. These results indicate that the single-molecule FCS detection system is capable of analyzing the binding characteristics of immune cell surface receptors even in difficult cases such as (1) small amount of protein samples, (2) small difference in molecular weight and (3) weak affinity. Therefore, it is a powerful tool for characterization and high throughput inhibitor screening of a wide variety of cell-cell recognition receptors involved in immunologically relevant events.

Amoxicillin conjugates to HLA class I molecules and interferes with signalling through the ILT2/LIR-1/CD85j inhibitory receptor

BACKGROUND

Drugs behave as haptens and are recognized by specific T-cell receptors in the context of major histocompatibility complex (MHC) molecules in allergic subjects. Natural killer cell receptors (NKRs) are MHC class I-specific receptors that modulate the threshold of activation of immunocompetent cells. Amongst them, ILT2/LIR-1/CD85j is an inhibitory NKR widely distributed in several cell lineages and with a broad spectrum of recognition of human leucocyte antigen (HLA) class I ligands.

METHODS

We have evaluated, at the biochemical and cellular level, the ability of amoxicillin (AX) conjugate to HLA class I molecules and to interfere with the inhibitory signal delivered by the HLA class I receptor ILT2/LIR-1/CD85j.

RESULTS

We have detected AX bound to cell membrane proteins and in particular to HLA class I molecules. Preincubation with AX rendered target cells susceptible to NK cell-mediated lysis. In conjugation experiments, target cell-bound AX hampered tyrosine phosphorylation of ILT2/LIR-1/CD85j upon ligand recognition and the subsequent recruitment of SHP-1 phosphatase.

CONCLUSION

Conjugation of AX to HLA class I molecules may mask HLA recognition by inhibitory receptors and attenuate the negative signal delivered by SHP-1 phosphatase, thus lowering the threshold of activation of effector cells.

Structural basis for recognition of the nonclassical MHC molecule HLA-G by the leukocyte Ig-like receptor B2 (LILRB2/LIR2/ILT4/CD85d)

HLA-G is a nonclassical MHC class I (MHCI) molecule that can suppress a wide range of immune responses in the maternal-fetal interface. The human inhibitory immune receptors leukocyte Ig-like receptor (LILR) B1 [also called LIR1, Ig-like transcript 2 (ILT2), or CD85j] and LILRB2 (LIR2/ILT4/CD85d) preferentially recognize HLA-G. HLA-G inherently exhibits various forms, including beta(2)-microglobulin (beta(2)m)-free and disulfide-linked dimer forms. Notably, LILRB1 cannot recognize the beta(2)m-free form of HLA-G or HLA-B27, but LILRB2 can recognize the beta(2)m-free form of HLA-B27. To date, the structural basis for HLA-G/LILR recognition remains to be examined. Here, we report the 2.5-A resolution crystal structure of the LILRB2/HLA-G complex. LILRB2 exhibits an overlapping but distinct MHCI recognition mode compared with LILRB1 and dominantly recognizes the hydrophobic site of the HLA-G alpha3 domain. NMR binding studies also confirmed these LILR recognition differences on both conformed (heavy chain/peptide/beta(2)m) and free forms of beta(2)m. Binding studies using beta(2)m-free MHCIs revealed differential beta(2)m-dependent LILR-binding specificities. These results suggest that subtle structural differences between LILRB family members cause the distinct binding specificities to various forms of HLA-G and other MHCIs, which may in turn regulate immune suppression.

Human ILT2 receptor associates with murine MHC class I moleculesin vivo and impairs T cell function

Immunoglobulin-like transcript 2 (ILT2/LILRB1/LIR1/CD85j) is an inhibitory receptor broadly expressed on leukocytes and antigen-presenting cells that recognizes HLA-class I and human cytomegalovirus UL18 proteins. The function of this receptor is to generate negative signals or to inhibit positive signals. Here, we demonstrate the model to study the function of ILT2 in vivo using a newly generated transgenic mouse expressing the human inhibitory receptor on T, B, NK, and NKT cells. ILT2 expression affects thymocyte development and targets the proximal TCR signaling pathway, resulting in long-term survival or acceptance of skin allografts. The phenotype and constitutive tyrosine phosphorylation of ILT2 in transgenic mice illustrate the possible existence of a murine ligand. We report here that H-2Db, a murine MHC class I molecule, associates with human ILT2 in vivo. This engagement with ILT2 directs effects on thymocyte development, negative regulation of TCR signaling, T cell activation, and alloimmune responses. Our finding provides support for an important inhibitory function of ILT2 in T cells in vivo and opens up strategies for targeting proximal TCR signaling for prevention of allograft rejection.

Increase in annexin V-positive B cells expressing LILRB1/ILT2/CD85j in malaria

The outcome of a Plasmodium falciparum infection differs greatly between patients, ranging from an asymptomatic carrier status to the most severe characteristics influenced by activating and inhibiting immune factors. The inhibitory leukocyte immunoglobulin-like receptor (LILRB1/CD85j) plays an important role in the immune response as regulator of cytotoxic T cells and of premature activation and clonal expansion of B cells. To investigate its role in malaria, we analyzed blood samples from malaria patients by cytometric analysis. We found a similar expression pattern of CD85j on PBMC in both patients and healthy children. However, malaria patients presented significantly more CD85j+ CD19+ B cells, which also bound annexin V an indicator of early cell death. We compared the plasma levels of several cytokines, since it was speculated that CD85j expression influences cytokine release. Production of inflammatory cytokines was significantly increased in severe malaria cases. We suggest that in malaria, dying B cells contribute to the overwhelming cytokine release and the impairment of the immune memory.

Decidual NK cells regulate key developmental processes at the human fetal-maternal interface

Human CD56(bright) NK cells accumulate in the maternal decidua during pregnancy and are found in direct contact with fetal trophoblasts. Several mechanisms have been proposed to explain the inability of NK cells to kill the semiallogeneic fetal cells. However, the actual functions of decidual NK (dNK) cells during pregnancy are mostly unknown. Here we show that dNK cells, but not peripheral blood-derived NK subsets, regulate trophoblast invasion both in vitro and in vivo by production of the interleukin-8 and interferon-inducible protein-10 chemokines. Furthermore, dNK cells are potent secretors of an array of angiogenic factors and induce vascular growth in the decidua. Notably, such functions are regulated by specific interactions between dNK-activating and dNK-inhibitory receptors and their ligands, uniquely expressed at the fetal-maternal interface. The overall results support a 'peaceful' model for reproductive immunology, in which elements of innate immunity have been incorporated in a constructive manner to support reproductive tissue development.

Soluble HLA-G Molecules Induce Apoptosis in Natural Killer Cells

Membrane-bound human leukocyte antigen-G (HLA-G) molecules are primarily expressed by cytotrophoblasts of the fetus. They are thought to protect the fetus from immunologic attack by the maternal immune system and have recently been associated with transplantation graft acceptance. In addition, soluble HLA-G molecules (sHLA-G) have been shown to play a role in the success of pregnancies, but are upregulated in certain cancers. However, the exact mechanism for this regulation has remained elusive. The aim of this study was to examine the mechanism by which sHLA-G interact with natural killer (NK) cells in vitro. sHLA-G effectively blocked NK lysis of target cells via fracticide killing of NK cells by apoptosis. These studies support the protective role of sHLA-G in immunologic reactions by interacting with NK cells, thus providing a regulatory function.

First report on the co-inheritance of (beta) IVS I-1 (G-->T) Thalassemia with the (gamma) CD85 [Phe-->Ser (F1) (TTT-->TCT)] HbA2 Etolia in Iran

Beta thalassemia minor phenotypes with normal HbA2 levels and decreased MCV and MCH values are relatively rare beta-thalassemia traits. Here, we describe a case with normal HbA2 and decreased MCV and MCH level. Amplification refractory mutation system-polymerase chain reaction(ARMS-PCR) revealed IVS I-1 (G-->T) mutation in the beta-globin gene. Direct sequencing of the delta-globin gene revealed a previously reported Hb variant called Hb A2 Etolia (Gene Bank Accession No. DQ106871). This is the first case reporting HbA2 Etolia in association with the beta-IVS I-1 (G-->T) mutation in Iran. Reduced HbA2 expression by a co-inherited HbA2 variant resulting in decreased HbA2, in Cis or Trans, may cause problems in carrier diagnostics and eventually in genetic counseling and prenatal diagnosis when insufficient molecular analyses are performed.

Spontaneous mutations in the human CMV HLA class I homologue UL18 affect its binding to the inhibitory receptor LIR-1/ILT2/CD85j

Human cytomegalovirus (HCMV) down-regulates cell surface expression of HLA class I molecules (HLA-I). UL18, an HCMV-encoded HLA-I homologue, has been proposed to protect virus-infected cells against NK cell recognition by engaging the inhibitory receptor leukocyte Ig-like receptor (LIR)-1, which also binds a broad spectrum of HLA-I alleles, including HLA-G1. Because genetic and biological differences exist among HCMV strains, we characterized laboratory (AD169) and clinical (4636, 13B, 109B) strain-derived UL18 proteins. Compared to the known AD169-derived UL18, mutations were found in clinical strain-derived UL18. They were clustered in the alpha3 domain (13B), previously shown to be critical for LIR-1 binding, or in the alpha1 domain (4636). Iotan cytotoxicity assays, pretreatment of LIR-1+ NKL with soluble 4636-UL18 completely abolished LIR-1-dependent protection from NK lysis, conferred by the expression of HLA-G1 on target cells (721.221-HLA-G1+). Similarly, flow cytometry, Biacore and ELISA experiments showed 4636-UL18 and 13B-UL18 to have the strongest binding capacity to LIR-1. Our results suggest the importance of two independent UL18 regions for LIR-1 binding, one localized on the tip of the alpha3 domain, and another composed of two loops that emerge from the alpha1 domain. Strain variations in these domains may result in different UL18-mediated effects on LIR-1+ cells during the course of HCMV infection.

Inhibitory receptors CD85j, LAIR-1, and CD152 down-regulate immunoglobulin and cytokine production by human B lymphocytes

Class switching consists in the substitution of the heavy-chain constant region of immunoglobulin M (IgM) with that of IgG, IgA, or IgE. This enables antibodies to acquire new effector functions that are crucial to combat invading pathogens. Class switching usually requires engagement of CD40 on B cells by CD40 ligand (CD40L) on antigen-activated CD4(+) T cells and the production of cytokines. The process must be regulated tightly because abnormal IgG and IgA production favors the onset of autoimmunity, whereas increased switching to IgE leads to atopy. These inflammatory disorders can be triggered or exacerbated by costimulatory signals. Although thoroughly investigated on T cells, the roles of the inhibitory receptors CD85j, LAIR-1, and CD152 on B-cell functions have not been fully elucidated. In this study we show that cross-linking of the B-cell inhibitory receptors by specific monoclonal antibodies inhibits IgG and IgE production, reduces the percentage of IgG- and IgE-expressing B cells, and down-regulates interleukin 8 (IL-8), IL-10, and tumor necrosis factor alpha production. These effects were demonstrated using different B-cell stimulatory pathways (recall antigens, CD40L-transfected cells plus IL-4, and lipopolysaccharide plus IL-4). It thus appears that CD85j, LAIR-1, and CD152 play a central role for the control of IL-4-driven isotype switching.

Evidence to Support the Role of HLA-G5 in Allograft Acceptance through Induction of Immunosuppressive/ Regulatory T Cells

The soluble HLA-G5 isoform encoded by intron-4 retaining spliced transcript has been previously detected in vivo in sera and grafts from transplanted patients who had significantly better graft acceptance. These findings led us to investigate the role of HLA-G5 in tolerance induction in vitro and its biological relevance in allograft acceptance in vivo. We demonstrated that engagement of Ig-like transcript-2 and Ig-like transcript-4 receptors by HLA-G5 is involved in inhibition of T cell alloproliferative responses. Naive T cells sensitized in vitro with HLA-G5, for as little as 18 h, 1) lost their ability to respond to subsequent allogeneic stimulus, and 2) acquired regulatory properties because they inhibited the reactivity of other T cells. These HLA-G5-induced T cells act in an Ag-nonspecific fashion and through soluble factors. Biological relevance was provided by ex vivo analyzes of samples from liver-kidney cotransplanted patients who had high HLA-G5 serum levels and no graft rejection. We showed that addition of HLA-G5-containing sera from these patients inhibited T cell alloresponses and that serum HLA-G5 was responsible for this inhibition. Notably, PBMC from transplanted patients exposed to high levels of circulating HLA-G5 did not respond to allostimulation and inhibited alloreactivity of other T cells. These results demonstrate that HLA-G5-mediated tolerance involves the induction of immunosuppressive T cells. These findings provide evidence supporting the tolerogenic properties of HLA-G and emphasize its potential application as a relevant therapeutic candidate capable of limiting allograft rejection.

Les lymphomes T épidermotropes comme modèles de progression tumorale

Primary cutaneous T cell lymphomas (CTCL) represent the most frequently occurring group of extra-nodal T cell lymphomas, originating from skin-homing memory T cells. Sezary syndrome (SS) is a leukemic variant of CTCL that presents with erythroderma, lymphadenopathies and presence of malignant T cells in peripheral blood. SS has an unfavourable prognosis, and is refractory to current treatments. Progress in understanding the pathogenesis and tumor progression of SS is limited. In the past few years, we have identified and reported several CTCL-associated antigens, CD158k/KIR3DL2, CD85j/ILT2, and SC5/vimentin. KIR3DL2 is the first phenotypic marker of Sezary cells that can be used for the diagnostic and follow-up of Sezary syndrome. The SC5 antibody is the only monoclonal antibody reacting with vimentin on the surface of viable Sezary cells. CTCL are characterized by a predominance of Th2 cytokines. The recent suggestion that CTCL cells could be regulatory T (Tr) cells remains controversial. Gene expression studies suggest that in the future we may develop new diagnostic and prognostic tools, and identify subsets of patients who would benefit from more appropriate treatment protocols. Future challenges are to render tumor cells sensitive to apoptosis by inhibiting specific signalling pathways such as the constitutively activated NF-KB pathway, to identify specific surface kinase receptors and to develop specific inhibitors, to develop humanized monoclonal antibodies directed against tumor specific antigens, able to kill tumor cells via complement-dependent and antibody-dependent cytotoxicity, and to stimulate innate immunity.

Transcriptional analysis of protective antigen-stimulated PBMC from non-human primates vaccinated with the anthrax vaccine absorbed

The transcriptional responses in recombinant protective antigen (PA)-stimulated peripheral blood mononuclear cells (PBMCs) from Anthrax Vaccine Absorbed (AVA)-vaccinated rhesus macaques were evaluated using Affymetrix HGU133 Plus 2.0 GeneChips. PBMCs from animals vaccinated at 0, 4, and 26 weeks were harvested at week 30, stimulated with PA, and RNA isolated. The expression of 295 unigenes was significantly increased in PA-stimulated compared to non-stimulated PBMCs; no significant decrease in gene expression was observed. These upregulated transcripts encoded for proteins functioning in both innate and adaptive immunity. Results were corroborated for several genes by real-time RT-PCR. This study provides information on the potential underlying transcriptional mechanisms in the immune response to PA in AVA-vaccinated rhesus macaques.

Expression, purification, and refolding of the myeloid inhibitory receptor leukocyte immunoglobulin-like receptor-5 for structural and ligand identification studies

The leukocyte immunoglobulin-like receptors (LIRs, also known as ILTs, CD85, and LILRs) comprise a family of related immunoregulatory receptors encoded within the leukocyte receptor cluster (LRC) on human chromosome 19. LIRs are transmembrane proteins containing either two or four extracellular immunoglobulin domains, and most family members are expressed predominantly on myeloid cell lineages. Although the inhibitory receptors LIR-1 and LIR-2 are known to bind to a broad range of class I MHC molecules and are thought to play important roles in immune regulation, the majority of LIRs are currently of unknown structure and their ligands remain unidentified. In this study, we describe recombinant production and characterisation of the extracellular portion of LIR-5 (ILT3), a poorly understood inhibitory receptor that transduces tolerising signals to dendritic cells. The two extracellular immunoglobulin domains of LIR-5 were expressed in Escherichia coli to a high level and were found to accumulate in inclusion bodies. Inclusion bodies were purified, solubilised, and receptor then renatured by dilution refolding, with acceptable yields. Size exclusion chromatography and SDS-PAGE analyses confirmed the extracellular portion behaved as a monomer in solution, and purified protein was antibody-reactive. LIR-5 is representative of a subset of LIR receptors that on the basis of structural and sequence comparisons with LIR-1 seem unlikely to bind class I MHC molecules. Successful prokaryotic generation of correctly folded LIR-5 in high levels has implications for production of other LRC receptors and should greatly facilitate attempts to define the structure and ligands of this important regulator of dendritic cell function.

Killer cell Ig-like receptor-dependent signaling by Ig-like transcript 2 (ILT2/CD85j/LILRB1/LIR-1)

Inhibitory killer cell Ig-like receptors (KIR) signal by recruitment of the tyrosine phosphatase Src homology region 2 domain-containing phosphatase-1 to ITIM. In the present study, we show that, surprisingly, KIR lacking ITIM are able to signal and inhibit in the human NK cell line NK92, but not in mouse NK cells. Signaling by mutant KIR is weaker than the wild-type receptor, does not require the transmembrane or cytoplasmic tail of KIR, and is blocked by overexpression of a catalytically inactive Src homology region 2 domain-containing phosphatase-1 molecule. We also demonstrate that mutant KIR signaling is blocked by Abs, which disrupt the interaction between KIR and human leukocyte Ag-C or Abs, which block the interaction between Ig-like transcript 2 (ILT2) and the alpha3 domain of HLA class I molecules. Thus, although ILT2 expressed in NK92 is insufficient to signal in response to human leukocyte Ag-C alone, ILT2 can signal in a KIR-dependent manner revealing functional cooperation between receptors encoded by two distinct inhibitory receptor families.

The CD85J/leukocyte inhibitory receptor-1 distinguishes between conformed and beta 2-microglobulin-free HLA-G molecules

For a proper development of the placenta, maternal NK cells should not attack the fetal extravillous cytotrophoblast cells. This inhibition of maternal NK cells is partially mediated via the nonclassical MHC class I molecule HLA-G. Recently, we demonstrated that HLA-G forms disulfide-linked high molecular complexes on the surface of transfected cells. In the present study, we demonstrate that HLA-G must associate with beta(2)m for its interaction with CD85J/leukocyte Ig-like receptor-1 (LIR-1). Although HLA-G free H chain complexes are expressed on the surface, they are not recognized and possibly interfere with CD85J/LIR-1 and HLA-G interaction. The formation of these complexes on the cell surface might represent a novel mechanism developed specifically by the HLA-G protein aimed to control the efficiency of the CD85J/LIR-1-mediated inhibition. We also show that endogenous HLA-G complexes are expressed on the cell surface. These findings provide novel insights into the delicate interaction between extravillous cytotrophoblast cells and NK cells in the decidua.

KIR3DL1 polymorphisms that affect NK cell inhibition by HLA-Bw4 ligand

The killer cell Ig-like receptor (KIR) gene family encodes MHC class I receptors expressed by NK cells and several T cell subpopulations. Factors contributing to human KIR haplotype diversity are differences in gene number, gene content, and allelic polymorphism. Whereas functional and clinical consequences of the first two factors are established, knowledge of the effects of KIR gene polymorphism is limited to special cases in which signaling function is reversed or cell surface expression lost. In this study we use retrovirally transduced human cell lines to show that 3DL1*002 is a stronger inhibitory receptor for HLA-Bw4 ligands than 3DL1*007. Analysis of mutant 3DL1*002 and 3DL1*007 molecules demonstrates that residue 238 in the D2 domain and 320 in the transmembrane region contribute to the difference in receptor strength. Neither position 238 nor 320 is predicted to interact directly with HLA-Bw4 ligand. This study also revealed that KIR3DL1 and LILRB1 both contribute to developing an inhibitory response to HLA-Bw4 ligands.

Entropically driven MHC class I recognition by human inhibitory receptor leukocyte Ig-like receptor B1 (LILRB1/ILT2/CD85j)

The human inhibitory receptor, leukocyte immunoglobulin (Ig)-like receptor B1 (also called Ig-like transcript (ILT) 2, CD85j), is broadly expressed on leukocytes. LILRB1 binds to a wide range of major histocompatibility complex class I molecules (MHCIs) and transduces negative signals that can, for example, prevent killing of MHCI-expressing cells. Here we report the kinetic, thermodynamic, NMR and crystallographic analyses of MHCI recognition by LILRB1. Kinetic studies demonstrated that LILRB1 binds to MHCIs with fast association and dissociation rates, typical of cell-cell recognition receptors. Thermodynamic analyses showed that LILRB1-MHCI interactions are entropically driven (-TdeltaS = -9.4 approximately -6.6 kcal mol(-1)) with low heat capacity changes (deltaC(p) = -0.22 approximately -0.10 kcal mol(-1) K(-1)). The crystal structures of LILRB1 in the different crystal forms exhibited variation in the elbow angle between the two N-terminal Ig-like domains, indicating interdomain flexibility. Consistently, NMR analysis provided the direct evidence of the conformational changes of LILRB1 upon the MHCI binding. These findings suggest that LILRB1-MHCI interactions, while involving some conformational adjustment, are not accompanied by a very large reduction in conformational flexibility at the binding interface. This mode of binding is distinct from "induced-fit" binding, which is associated with large reductions in conformational flexibility, and would be suitable for rapid engagement of MHCIs to enable fast monitoring of the expression level of MHCIs on target cells.

Expression of Leukocyte Immunoglobulin-Like Receptors and Natural Killer Receptors on Virus-Specific CD8+T Cells during the Evolution of Epstein-Barr Virus-Specific Immune Responsesin Vivo

Antigen-primed cytotoxic T lymphocytes (CTL) may express leukocyte immunoglobulin-like receptors (LILRs) and natural killer receptors (NKRs). Published work suggests that expression of some of these receptors confers survival advantage, leading to the idea that cells expressing such receptors may accumulate as an antigen-specific response evolves. Here we tested this hypothesis by analyzing expression of CD85j (also known as LILRB1 or ILT2), KIRs, CD94, and CD161 by Epstein- Barr virus (EBV)-specific CTL during the primary and persistent phases of EBV infection in humans. During primary infection, few EBV-specific CTL expressed these receptors and this proportion was equally low in early persistent infection. Thus, expression of these molecules does not influence capacity to survive downregulation of the primary response. However, in donors persistently infected with EBV for many years, a significantly higher proportion of EBV-specific CTL expressed CD85j and NKRs, suggesting that cells expressing these receptors can accumulate with time. Using FACS analysis, we confirmed, at a single cell level, that expression of CD85j, defined by staining with the antibody VMP55, was associated with reduced capacity of EBV-specific CD8+ T cells to respond to antigen. Thus, in the later stages of persistent infection, protective immunity to EBV may be reduced due to the preferential accumulation of hyporesponsive EBV-specific CD8+ T cells.

Expression of the immune-tolerogenic major histocompatibility molecule HLA-G in multiple sclerosis: implications for CNS immunity

HLA-G is a non-classical major histocompatibility complex (MHC) class I antigen with highly limited tissue distribution under non-pathological conditions. Although capable of acting as a peptide-presenting molecule, its strong immune-inhibitory properties identify HLA-G as a mediator of immune tolerance with specific relevance at immune-privileged sites such as trophoblast or thymus. To assess the role of HLA-G in CNS immunity, we investigated its expression in brain specimens from patients with multiple sclerosis (n = 11), meningitis (n = 2) and Alzheimer's disease (n = 2) and non-pathological CNS controls (n = 6). Furthermore, cultured human microglial cells and CSF of patients with multiple sclerosis and controls were assessed. Furthermore, CSF from MS patients and controls, as well as cultured human microglial cells were assessed. Using several HLA-G specific mAb and immunohistochemistry, HLA-G protein was found strongly expressed in brain specimens from patients with multiple sclerosis while it was rarely detectable in the non-pathological control specimens. In multiple sclerosis brain specimens, HLA-G immunoreactivity was observed in acute plaques, in chronic active plaques, in perilesional areas as well as in normal appearing white matter. In all areas microglial cells, macrophages, and in part endothelial cells were identified as the primary cellular source of expression. HLA-G was also found in other disease entities (meningitis, Alzheimer's specimens) where expression correlated to activation and MHC class II expression on microglial cells. Importantly, ILT2, a receptor for HLA-G, was also found in multiple sclerosis brain specimens thus emphasizing the relevance of this inhibitory pathway in vivo. HLA-G mRNA and protein expression and regulation could also be corroborated on cultured human microglial cells in vitro. Further, expression of HLA-G in the CSF of multiple sclerosis patients and controls was analysed by flow cytometry and ELISA. Monocytes represented the main source of cellular HLA-G expression in the CSF. Corresponding to the observations with the tissue specimens, CSF mean levels of soluble HLA-G were significantly higher in multiple sclerosis than in non-inflammatory controls (171 +/- 31 versus 39 +/- 10 U/ml; P = 0.0001). The demonstration of HLA-G and its receptor ILT2 on CNS cells and in areas of microglia activation implicate HLA-G as a contributor to the fundamental mechanisms regulating immune reactivity in the CNS. This pathway may act as an inhibitory feedback aimed to downregulate the deleterious effects of T-cell infiltration in neuroinflammation.

Genetic variability of the major histocompatibility complex class I homologue encoded by human cytomegalovirus leads to differential binding to the inhibitory receptor ILT2

Human cytomegalovirus carries a gene, UL18, that is homologous to cellular major histocompatibility complex (MHC) class I genes. Like MHC class I molecules, the protein product of the UL18 gene associates with beta2-microglobulin, and the stability of this complex depends on peptide loading. UL18 protein binds to ILT2 (CD85j), an inhibitory receptor present on B cells, monocytes, dendritic cells, T cells, and NK cells that also recognizes classical and nonclassical MHC molecules. These observations suggest that UL18 may play a role in viral immune evasion, but its real function is unclear. Since this molecule has similarity with polymorphic MHC proteins, we explored whether the UL18 gene varied between virus isolates. We report here that the UL18 gene varies significantly between virus isolates: amino acid substitutions were found in the predicted alpha1, alpha2, and alpha3 domains of the UL18 protein molecule. We also studied the ability of several variant UL18 proteins to bind to the ILT2 receptor. All of the variants tested bound to ILT2, but there were marked differences in the affinity of binding to this receptor. These differences were reflected in functional assays measuring inhibition of the cytotoxic capacity of NK cells via interaction with ILT2. In addition, the variants did not bind other members of the CD85 family. The implications of these data are discussed.

CD85j (leukocyte Ig-like receptor-1/Ig-like transcript 2) inhibits human osteoclast-associated receptor-mediated activation of human dendritic cells

Immature dendritic cells (DCs) derived from freshly isolated human monocytes were used to evaluate the effect of the inhibiting receptor CD85j (leukocyte Ig-like receptor-1/ILT2) on activation induced by cross-linking of the human osteoclast-associated receptor (hOSCAR). CD85j and hOSCAR were expressed consistently at the same density on monocytes and on monocyte-derived DCs (both immature and mature). Cross-linking of hOSCAR, which activates via the FcR-associated gamma-chain, induced Ca(2+) flux in DCs. Concomitant cross-linking of anti-CD85j mAb abolished this early activation event. Likewise, CD85j stimulation strongly reduced IL-8 and IL-12 production by hOSCAR-activated DCs. Inhibition of DCs via CD85j also impaired their ability to enhance Ag-specific T cell proliferation induced by hOSCAR. Finally, because hOSCAR prevents apoptosis of DCs in the absence of growth/survival factors, CD85j cross-linking was able to counteract completely this antiapoptotic effect and to reduce Bcl-2 expression enhanced by hOSCAR stimulation. Thus, CD85j is an inhibiting receptor that is functional in human DCs.

Molecular cloning of LILRC1 and LILRC2 in the mouse and the rat, two novel immunoglobulin-like receptors encoded by the leukocyte receptor gene complex

We report the molecular cloning of two novel single-member receptor families with homology to LILR/CD85, PIR, and gp49: LILRC1 in the rat and the mouse, and LILRC2 in the rat. LILRC1 and LILRC2 both have two extracellular Ig-like domains and a cytoplasmic tail devoid of any known signaling motifs. The transmembrane regions of LILRC1 and LILRC2 contain an arginine residue, a common feature in receptors that associate with activating adaptor proteins. Rat and mouse LILRC1 are orthologs sharing 81.5% amino acid identity. LILRC2 represents a distinct receptor family, 47.9% identical to LILRC1. No murine LILRC2 ortholog was detected in genome or expressed sequence tag sequence databases. By radiation hybrid mapping, the rat Lilrc1 and Lilrc2 loci were localized to the leukocyte receptor gene complex (LRC) on chromosome 1, and the mouse Lilrc1 locus was mapped to the LRC on chromosome 7. Moreover, the mouse and rat Lilrc1 loci were localized to similar positions within the LRC. As shown by RT-PCR, rat LILRC1 was expressed by B cells, neutrophils, and a macrophage cell line. Transcription of LILRC2 was detected in T cells, B cells, neutrophils, and macrophages.

Extensive polymorphisms of LILRB1 (ILT2, LIR1) and their association with HLA-DRB1 shared epitope negative rheumatoid arthritis

Leukocyte immunoglobulin-like receptor subfamily B member 1 (LILRB1/LIR1/ILT2) is an inhibitory receptor broadly expressed on leukocytes and recognizes HLA-class I and human cytomegalovirus UL18. LILRB1 is encoded within the leukocyte receptor complex on 19q13.4, previously implicated to be a susceptibility region to systemic lupus erythematosus (SLE). In this study, we screened for polymorphisms of LILRB1 and examined their association with SLE and rheumatoid arthritis (RA). In the 5' portion of LILRB1, three haplotypes containing four non-synonymous substitutions within the ligand-binding domains and two single nucleotide polymorphisms within the promoter region were identified and designated as PE01-03. In the 3' portion, two haplotypes (CY01, 02) containing a non-synonymous substitution of the cytoplasmic region were identified. CY01 and 02 did not co-segregate with PE01-03. Significant association with susceptibility to SLE or RA was not observed; however, among the subjects not carrying RA-associated HLA-DRB1 shared epitope (SE), LILRB1.PE01/01 diplotype was significantly associated with RA (odds ratio 2.05, P = 0.019 and Pc = 0.038). Gross difference was not observed in the crystal structures, thermostabilities and binding affinities to HLA-class I ligands among LILRB1.PE01-03 haplotype products; however, surface expression of LILRB1 was significantly decreased in lymphocytes and monocytes from the carriers of PE01 haplotype. These findings demonstrated that LILRB1 is highly polymorphic and is associated with susceptibility to RA in HLA-DRB1 SE negative subjects, possibly by insufficient inhibitory signaling in leukocytes. In addition, these observations suggested that the polymorphisms of LILR family members may be substantially involved in the diversity of human immune responses.