Functional requirements for interactions between CD84 and Src homology 2 domain-containing proteins and their contribution to human T cell activation

Unraveling genomic diversity and positive selection signatures of Qaidam cattle through whole-genome re-sequencing

Qaidam cattle are a typical Chinese native breed inhabiting northwest China. They bear the characteristics of high cold and roughage tolerance, low-oxygen adaptability and good meat quality. To analyze the genetic diversity of Qaidam cattle, 60 samples were sequenced using whole-genome resequencing technology, along with 192 published sets of whole-genome sequencing data of Indian indicine cattle, Chinese indicine cattle, North Chinese cattle breeds, East Asian taurine cattle, Eurasian taurine cattle and European taurine cattle as controls. It was found that Qaidam cattle have rich genetic diversity in Bos taurus, but the degree of inbreeding is also high, which needs further protection. The phylogenetic analysis, principal component analysis and ancestral component analysis showed that Qaidam cattle mainly originated from East Asian taurine cattle. Qaidam cattle had a closer genetic relationship with the North Chinese cattle breeds and the least differentiation from Mongolian cattle. Annotating the selection signals obtained by composite likelihood ratio, nucleotide diversity analysis, integrated haplotype score, genetic differentiation index, genetic diversity ratio and cross-population extended haplotype homozygosity methods, several genes associated with immunity, reproduction, meat, milk, growth and adaptation showed strong selection signals. In general, this study provides genetic evidence for understanding the germplasm characteristics of Qaidam cattle. At the same time, it lays a foundation for the scientific and reasonable protection and utilization of genetic resources of Chinese local cattle breeds, which has great theoretical and practical significance.

T cell co-stimulatory and co-inhibitory pathways in atopic dermatitis

The use of immune checkpoint inhibitors (ICIs) targeting the T cell inhibitory pathways has revolutionized cancer treatment. However, ICIs might induce progressive atopic dermatitis (AD) by affecting T cell reactivation. The critical role of T cells in AD pathogenesis is widely known. T cell co-signaling pathways regulate T cell activation, where co-signaling molecules are essential for determining the magnitude of the T cell response to antigens. Given the increasing use of ICIs in cancer treatment, a timely overview of the role of T cell co-signaling molecules in AD is required. In this review, we emphasize the importance of these molecules involved in AD pathogenesis. We also discuss the potential of targeting T cell co-signaling pathways to treat AD and present the unresolved issues and existing limitations. A better understanding of the T cell co-signaling pathways would aid investigation of the mechanism, prognosis evaluation, and treatment of AD.

Differentiation-related genes in tumor-associated macrophages as potential prognostic biomarkers in non-small cell lung cancer

Background

The purpose of this study was to evaluate the role of differentiation-related genes (DRGs) in tumor-associated macrophages (TAMs) in non-small cell lung cancer (NSCLC).

Methods

Single cell RNA-seq (scRNA-seq) data from GEO and bulk RNA-seq data from TCGA were analyzed to identify DRGs using trajectory method. Functional gene analysis was carried out by GO/KEGG enrichment analysis. The mRNA and protein expression in human tissue were analyzed by HPA and GEPIA databases. To investigate the prognostic value of these genes, three risk score (RS) models in different pathological types of NSCLC were generated and predicted NSCLC prognosis in datasets from TCGA, UCSC and GEO databases.

Results

1,738 DRGs were identified through trajectory analysis. GO/KEGG analysis showed that these genes were predominantly related to myeloid leukocyte activation and leukocyte migration. 13 DRGs (C1QB, CCL4, CD14, CD84, FGL2, MS4A6A, NLRP3, PLEK, RNASE6, SAMSN1, SPN, TMEM176B, ZEB2) related to prognosis were obtained through univariate Cox analysis and Lasso regression. C1QB, CD84, FGL2, MS4A6A, NLRP3, PLEK, SAMSN1, SPN, and ZEB2 were downregulated in NSCLC compared to non-cancer tissue. The mRNA of 13 genes were significantly expressed in pulmonary macrophages with strong cell specificity. Meanwhile, immunohistochemical staining showed that C1QB, CCL4, SPN, CD14, NLRP3, SAMSN1, MS4A6A, TMEM176B were expressed in different degrees in lung cancer tissues. ZEB2 (HR=1.4, P<0.05) and CD14 (HR=1.6, P<0.05) expression were associated with a worse prognosis in lung squamous cell carcinoma; ZEB2 (HR=0.64, P<0.05), CD84 (HR=0.65, P<0.05), PLEK (HR=0.71, P<0.05) and FGL2 (HR=0.61, P<0.05) expression were associated with a better prognosis in lung adenocarcinoma. Three RS models based on 13 DRGs both showed that the high RS was significantly associated with poor prognosis in different pathological types of NSCLC.

Conclusions

This study highlights the prognostic value of DRGs in TAMs in NSCLC patients, providing novel insights for the development of therapeutic and prognostic targets based on TAM functional differences.

Pharmacogenetics of Drug Therapies in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disorder that can lead to severe joint damage and is often associated with a high morbidity and disability. Disease-modifying anti-rheumatic drugs (DMARDs) are the mainstay of treatment in RA. DMARDs not only relieve the clinical signs and symptoms of RA but also inhibit the radiographic progression of disease and reduce the effects of chronic systemic inflammation. Since the introduction of biologic DMARDs in the late 1990s, the therapeutic range of options for the management of RA has significantly expanded. However, patients' response to these agents is not uniform with considerable variability in both efficacy and toxicity. There are no reliable means of predicting an individual patient's response to a given DMARD prior to initiation of therapy. In this chapter, the current published literature on the pharmacogenetics of traditional DMARDS and the newer biologic DMARDs in RA is highlighted. Pharmacogenetics may help individualize drug therapy in patients with RA by providing reliable biomarkers to predict medication toxicity and efficacy.

CD84 Links T Cell and Platelet Activity in Cerebral Thrombo-Inflammation in Acute Stroke

RATIONALE

Ischemic stroke is a leading cause of morbidity and mortality worldwide. Recanalization of the occluded vessel is essential but not sufficient to guarantee brain salvage. Experimental and clinical data suggest that infarcts often develop further due to a thromboinflammatory process critically involving platelets and T cells, but the underlying mechanisms are unknown.

OBJECTIVE

We aimed to determine the role of CD (cluster of differentiation)-84 in acute ischemic stroke after recanalization and to dissect the underlying molecular thromboinflammatory mechanisms.

METHODS AND RESULTS

Here, we show that mice lacking CD84-a homophilic immunoreceptor of the SLAM (signaling lymphocyte activation molecule) family-on either platelets or T cells displayed reduced cerebral CD4+ T-cell infiltration and thrombotic activity following experimental stroke resulting in reduced neurological damage. In vitro, platelet-derived soluble CD84 enhanced motility of wild-type but not of Cd84-/- CD4+ T cells suggesting homophilic CD84 interactions to drive this process. Clinically, human arterial blood directly sampled from the ischemic cerebral circulation indicated local shedding of platelet CD84. Moreover, high platelet CD84 expression levels were associated with poor outcome in patients with stroke.

CONCLUSIONS

These results establish CD84 as a critical pathogenic effector and thus a potential pharmacological target in ischemic stroke.

SLAM family member 8 is involved in oncogenic KIT-mediated signalling in human mastocytosis

The signalling lymphocytic activation molecule family member 8 (SLAMF8)/CD353 is a member of the CD2 family of proteins. Its ligand has not been identified. SLAMF8 is expressed by macrophages and suppresses cellular functions. No study has yet explored SLAMF8 expression or function in human mastocytosis, which features oncogenic KIT-mediated proliferation of human mast cells. SLAMF8 protein was expressed in human mastocytosis cells, immunohistochemically. SLAMF8 expression was also evident in the human mast cell lines, HMC1.2 (expressing oncogenic KIT) and LAD2 (expressing wild-type KIT) cells. SLAMF8 knock-down significantly reduced the KIT-mediated growth of HMC1.2 cells but not that of LAD2 cells. SLAMF8 knock-down HMC1.2 cells exhibited significant attenuation of SHP-2 activation and oncogenic KIT-mediated RAS-RAF-ERK signalling. An interaction between SLAMF8 and SHP-2 was confirmed in HMC1.2 cells and all pathological mastocytosis specimens examined (19 of 19 cases, 100%). Thus, SLAMF8 is involved in oncogenic KIT-mediated RAS-RAF-ERK signalling and the subsequent growth of human neoplastic mast cells mediated by SHP-2. SLAMF8 is a possible therapeutic target in human mastocytosis patients.

CD84 cell surface signaling molecule: An emerging biomarker and target for cancer and autoimmune disorders

CD84 (SLAMF5) is a member of the SLAM family of cell-surface immunoreceptors. Broadly expressed on most immune cell subsets, CD84 functions as a homophilic adhesion molecule, whose signaling can activate or inhibit leukocyte function depending on the cell type and its stage of activation or differentiation. CD84-mediated signaling regulates diverse immunological processes, including T cell cytokine secretion, natural killer cell cytotoxicity, monocyte activation, autophagy, cognate T:B interactions, and B cell tolerance at the germinal center checkpoint. Recently, alterations in CD84 have been related to autoimmune and lymphoproliferative disorders. Specific allelic variations in CD84 are associated with autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. In chronic lymphocytic leukemia, CD84 mediates intrinsic and stroma-induced survival of malignant cells. In this review, we describe our current understanding of the structure and function of CD84 and its potential role as a therapeutic target and biomarker in inflammatory autoimmune disorders and cancer.

The SLAM family receptors: Potential therapeutic targets for inflammatory and autoimmune diseases

The signaling lymphocytic activation molecule (SLAM) family is comprised of nine distinct receptors (SLAMF1 through SLAMF9) that are expressed on hematopoietic cells. All of these receptors, with the exception of SLAMF4, are homotypic by nature as downstream signaling occurs when hematopoietic cells that express the same SLAM receptor interact. The SLAM family receptor function is largely controlled via SLAM associated protein (SAP) family adaptors. The SAP family adaptors consist of SAP, Ewing sarcoma associated transcript (EAT)-2, and EAT-2-related transducer (ERT). These adaptors associate with the cytoplasmic domain of the SLAM family receptors through phosphorylated tyrosines. Defects in SLAM family members and SAP adaptors have been implicated in causing immune deficiencies. This is exemplified in patients with X-linked lymphoproliferative (XLP) disease, where SAP undergoes a loss of function mutation. Furthermore, evidence has been accumulating that SLAM family members are potential targets for inflammatory and autoimmune diseases. This review will discuss the structure and function of the SLAM family receptors and SAP family adaptors, their role in immune regulation, and potential approaches to target this family of receptors therapeutically.

Precision Medicine in Rheumatoid Arthritis

Treatment of rheumatoid arthritis (RA) has substantially improved in recent years because of the development of novel drugs. However, response is not universal for any of the treatment options, and selection of an effective therapy is currently based on a trial-and-error approach. Delayed treatment response increases the risk of progressive joint damage and resultant disability and also has a significant impact on quality of life for patients. For many drugs, the patient's genetic background influences response to therapy, and understanding the genetics of response to therapy in RA may allow for targeted personalized health care.

Signaling Lymphocyte Activation Molecule Family 5 Enhances Autophagy and Fine-Tunes Cytokine Response in Monocyte-Derived Dendritic Cells via Stabilization of Interferon Regulatory Factor 8

Signaling lymphocyte activation molecule family (SLAMF) receptors are essential regulators of innate and adaptive immune responses. The function of SLAMF5/CD84, a family member with almost ubiquitous expression within the hematopoietic lineage is poorly defined. In this article, we provide evidence that in human monocyte-derived dendritic cells (moDCs) SLAMF5 increases autophagy, a degradative pathway, which is highly active in dendritic cells (DCs) and plays a critical role in orchestration of the immune response. While investigating the underlying mechanism, we found that SLAMF5 inhibited proteolytic degradation of interferon regulatory factor 8 (IRF8) a master regulator of the autophagy process by a mechanism dependent on the E3-ubiquitin ligase tripartite motif-containing protein 21 (TRIM21). Furthermore, we demonstrate that SLAMF5 influences the ratio of CD1a⁺ cells in differentiating DCs and partakes in the regulation of IL-1β, IL-23, and IL-12 production in LPS/IFNγ-activated moDCs in a manner that is consistent with its effect on IRF8 stability. In summary, our experiments identified SLAMF5 as a novel cell surface receptor modulator of autophagy and revealed an unexpected link between the SLAMF and IRF8 signaling pathways, both implicated in multiple human pathologies.

Identification of hub genes of pneumocyte senescence induced by thoracic irradiation using weighted gene co‑expression network analysis

Irradiation commonly causes pneumocyte senescence, which may lead to severe fatal lung injury characterized by pulmonary dysfunction and respiratory failure. However, the molecular mechanism underlying the induction of pneumocyte senescence by irradiation remains to be elucidated. In the present study, weighted gene co-expression network analysis (WGCNA) was used to screen for differentially expressed genes, and to identify the hub genes and gene modules, which may be critical for senescence. A total of 2,916 differentially expressed genes were identified between the senescence and non-senescence groups following thoracic irradiation. In total, 10 gene modules associated with cell senescence were detected, and six hub genes were identified, including B-cell scaffold protein with ankyrin repeats 1, translocase of outer mitochondrial membrane 70 homolog A, actin filament-associated protein 1, Cd84, Nuf2 and nuclear factor erythroid 2. These genes were markedly associated with cell proliferation, cell division and cell cycle arrest. The results of the present study demonstrated that WGCNA of microarray data may provide further insight into the molecular mechanism underlying pneumocyte senescence.

Mice lacking the SLAM family member CD84 display unaltered platelet function in hemostasis and thrombosis

Background

Platelets are anuclear cell fragments derived from bone marrow megakaryocytes that safeguard vascular integrity by forming thrombi at sites of vascular injury. Although the early events of thrombus formation—platelet adhesion and aggregation—have been intensively studied, less is known about the mechanisms and receptors that stabilize platelet-platelet interactions once a thrombus has formed. One receptor that has been implicated in this process is the signaling lymphocyte activation molecule (SLAM) family member CD84, which can undergo homophilic interactions and becomes phosphorylated upon platelet aggregation.

Objective

The role of CD84 in platelet physiology and thrombus formation was investigated in CD84-deficient mice.

Methods and Results

We generated CD84-deficient mice and analyzed their platelets in vitro and in vivo. Cd84^−/− platelets exhibited normal activation and aggregation responses to classical platelet agonists. Furthermore, CD84 deficiency did not affect integrin-mediated clot retraction and spreading of activated platelets on fibrinogen. Notably, also the formation of stable three-dimensional thrombi on collagen-coated surfaces under flow ex vivo was unaltered in the blood of Cd84^−/− mice. In vivo, Cd84^−/− mice exhibited unaltered hemostatic function and arterial thrombus formation.

Conclusion

These results show that CD84 is dispensable for thrombus formation and stabilization, indicating that its deficiency may be functionally compensated by other receptors or that it may be important for platelet functions different from platelet-platelet interactions.

Quantitative genetics in the study of virus-induced disease

While the role of viral variants has long been known to play a key role in causing variation in disease severity, it is also clear that host genetic variation plays a critical role in determining virus-induced disease responses. However, a variety of factors, including confounding environmental variables, rare genetic variants requiring extremely large cohorts, the temporal dynamics of infections, and ethical limitation on human studies, have made the identification and dissection of variant host genes and pathways difficult within human populations. This difficulty has led to the development of a variety of experimental approaches used to identify host genetic contributions to disease responses. In this chapter, we describe the history of genetic associations within the human population, the development of experimentally tractable systems, and the insights these specific approaches provide. We conclude with a discussion of recent advances that allow for the investigation of the role of complex genetic networks that underlie host responses to infection, with the goal of drawing connections to human infections. In particular, we highlight the need for robust animal models with which to directly control and assess the role of host genetics on viral infection outcomes.

SAP facilitates recruitment and activation of LCK at NTB-A receptors during restimulation-induced cell death

Upon TCR restimulation, activated, cycling T cells can undergo a self-regulatory form of apoptosis known as restimulation-induced cell death (RICD). We previously demonstrated that RICD is impaired in T cells from patients with X-linked lymphoproliferative disease, which lack SLAM-associated protein (SAP) expression. Both SAP and the specific SLAM receptor NK, T, and B cell Ag (NTB-A) are required for RICD, but the mechanism by which these molecules promote a strong, proapoptotic signal through the TCR remains unclear. In this article, we show that the Src-family kinase LCK, but not FYN, associates with NTB-A in activated human T cells. This association increased after TCR restimulation in a SAP-dependent manner, requiring both immunoreceptor tyrosine-based switch motifs in the NTB-A cytoplasmic tail. Both NTB-A-associated LCK phosphorylation and kinase activity were enhanced in restimulated T cells, amplifying proximal TCR signaling. In contrast, TCR-induced LCK association with NTB-A, as well as phosphorylation and kinase activity, was reduced in T cells from patients with X-linked lymphoproliferative disease or normal T cells transfected with SAP-specific small interfering RNA, consistent with RICD resistance. Collectively, our data reveal how SAP nucleates a previously unknown signaling complex involving NTB-A and LCK to potentiate RICD of activated human T cells.

Genome-wide association study and gene expression analysis identifies CD84 as a predictor of response to etanercept therapy in rheumatoid arthritis

Anti-tumor necrosis factor alpha (anti-TNF) biologic therapy is a widely used treatment for rheumatoid arthritis (RA). It is unknown why some RA patients fail to respond adequately to anti-TNF therapy, which limits the development of clinical biomarkers to predict response or new drugs to target refractory cases. To understand the biological basis of response to anti-TNF therapy, we conducted a genome-wide association study (GWAS) meta-analysis of more than 2 million common variants in 2,706 RA patients from 13 different collections. Patients were treated with one of three anti-TNF medications: etanercept (n = 733), infliximab (n = 894), or adalimumab (n = 1,071). We identified a SNP (rs6427528) at the 1q23 locus that was associated with change in disease activity score (ΔDAS) in the etanercept subset of patients (P = 8 × 10(-8)), but not in the infliximab or adalimumab subsets (P>0.05). The SNP is predicted to disrupt transcription factor binding site motifs in the 3' UTR of an immune-related gene, CD84, and the allele associated with better response to etanercept was associated with higher CD84 gene expression in peripheral blood mononuclear cells (P = 1 × 10(-11) in 228 non-RA patients and P = 0.004 in 132 RA patients). Consistent with the genetic findings, higher CD84 gene expression correlated with lower cross-sectional DAS (P = 0.02, n = 210) and showed a non-significant trend for better ΔDAS in a subset of RA patients with gene expression data (n = 31, etanercept-treated). A small, multi-ethnic replication showed a non-significant trend towards an association among etanercept-treated RA patients of Portuguese ancestry (n = 139, P = 0.4), but no association among patients of Japanese ancestry (n = 151, P = 0.8). Our study demonstrates that an allele associated with response to etanercept therapy is also associated with CD84 gene expression, and further that CD84 expression correlates with disease activity. These findings support a model in which CD84 genotypes and/or expression may serve as a useful biomarker for response to etanercept treatment in RA patients of European ancestry.

CD84 is a survival receptor for CLL cells

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of CD5+ B lymphocytes in peripheral blood, lymphoid organs and bone marrow. The main feature of the disease is accumulation of the malignant cells due to decreased apoptosis. CD84 belongs to the signaling lymphocyte activating molecule family of immunoreceptors, and has an unknown function in CLL cells. Here, we show that the expression of CD84 is significantly elevated from the early stages of the disease, and is regulated by macrophage migration inhibitory factor and its receptor, CD74. Activation of cell surface CD84 initiates a signaling cascade that enhances CLL cell survival. Both downmodulation of CD84 expression and its immune-mediated blockade induce cell death in vitro and in vivo. In addition, analysis of samples derived from an on-going clinical trial, in which human subjects were treated with humanized anti-CD74 (milatuzumab), shows a decrease in CD84 messenger RNA and protein levels in milatuzumab-treated cells. This downregulation was correlated with reduction of Bcl-2 and Mcl-1 expression. Thus, our data show that overexpression of CD84 in CLL is an important survival mechanism that appears to be an early event in the pathogenesis of the disease. These findings suggest novel therapeutic strategies based on the blockade of this CD84-dependent survival pathway.

Decreased microRNA-142-3p/5p expression causes CD4+ T cell activation and B cell hyperstimulation in systemic lupus erythematosus

OBJECTIVE

To examine the role of microRNA-142-3p/5p (miR-142-3p/5p) in the development of autoimmunity in patients with systemic lupus erythematosus (SLE).

METHODS

MicroRNA-142-3p/5p expression levels were determined by real-time quantitative polymerase chain reaction, and potential target genes were verified using luciferase reporter gene assays. The effects of miR-142-3p/5p on T cell function were assessed by transfection with miR-142-3p/5p inhibitors or mimics. Histone modifications and methylation levels within a putative regulatory region of the miR-142 locus were detected by chromatin immunoprecipitation assay and bisulfite sequencing, respectively.

RESULTS

We confirmed that miR-142-3p and miR-142-5p were significantly down-regulated in SLE CD4+ T cells compared with healthy controls and observed that miR-142-3p/5p levels were inversely correlated with the putative SLE-related targets signaling lymphocytic activation molecule-associated protein (SAP), CD84, and interleukin-10 (IL-10). We demonstrated that miR-142-3p and miR-142-5p directly inhibit SAP, CD84, and IL-10 translation, and that reduced miR-142-3p/5p expression in CD4+ T cells can significantly increase protein levels of these target genes. Furthermore, inhibiting miR-142-3p/5p in healthy donor CD4+ T cells caused T cell overactivation and B cell hyperstimulation, whereas overexpression of miR-142-3p/5p in SLE CD4+ T cells had the opposite effect. We also observed that the decrease in miR-142 expression in SLE CD4+ T cells correlated with changes to histone modifications and DNA methylation levels upstream of the miR-142 precursor sequence.

CONCLUSION

The results of this study indicate that reduced expression of miR-142-3p/5p in the CD4+ T cells of patients with SLE causes T cell activity and B cell hyperstimulation.

The SLAM family member CD84 is regulated by ADAM10 and calpain in platelets

BACKGROUND AND OBJECTIVE

Ectodomain shedding is a major mechanism to modulate platelet receptor signaling and to downregulate platelet reactivity. Proteins of the a disintegrin and metalloproteinase (ADAM) family are implicated in the shedding of various platelet receptors. The signaling lymphocyte activation molecule (SLAM) family receptor CD84 is highly expressed in platelets and immune cells, but its role in platelet physiology is not well explored. Because of its ability to form homodimers, CD84 has been suggested to mediate contact-dependent signaling and contribute to thrombus stability. However, nothing is known about the cellular regulation of CD84.

METHODS

We studied the regulation of CD84 in murine platelets by biochemical approaches and use of three different genetically modified mouse lines. Regulation of CD84 in human platelets was studied using inhibitors and biochemical approaches.

RESULTS

We show that CD84 is cleaved from the surface of human and murine platelets in response to different shedding inducing agents and platelet receptor agonists. CD84 downregulation occurs through ectodomain-shedding and intracellular cleavage. Studies in transgenic mice identified ADAM10 as the principal sheddase responsible for CD84 cleavage, whereas ADAM17 was dispensable. Western blot analyses revealed calpain-mediated intracellular cleavage of the CD84 C-terminus, occurring simultaneously with, but independently of, ectodomain shedding. Furthermore, analysis of plasma and serum samples from transgenic mice demonstrated that CD84 is constitutively shed from the platelet surface by ADAM10 in vivo.

CONCLUSIONS

These results reveal a dual regulation mechanism for platelet CD84 by simultaneous extra- and intracellular cleavage that may modulate platelet-platelet and platelet-immune cell interactions.

CD84 negatively regulates IgE high-affinity receptor signaling in human mast cells

CD84 is a self-binding receptor from the CD150 (or signaling lymphocyte activation molecule [SLAM]) family that is broadly expressed in hematopoietic cells. It has been described that the adaptors SLAM-associated protein (SAP) and EWS-FLI1-activated transcript 2 (EAT-2) are critical for CD150 family members' signaling and function. We observed that human mast cells express CD84 but lack SAP or EAT-2, that CD84 is tyrosine phosphorylated upon FcεRI engagement, and that the release of granule contents is reduced when FcεRI is coengaged with CD84 in LAD2 and human CD34(+)-derived mast cells. In addition, we observed that the release of IL-8 and GM-CSF was also reduced in FcεRI/CD84-costimulated cells as compared with FcεRI/Ig control. To understand how CD84 downregulates FcεRI-mediated function, we analyzed signaling pathways affected by CD84 in human mast cells. Our results showed that CD84 dampens FcεRI-mediated calcium mobilization after its co-cross-linking with the receptor. Furthermore, FcεRI-mediated Syk-linker for activation of T cells-phospholipase C-γ1 axis activity is downregulated after CD84 stimulation, compared with FcεRI/Ig control. The inhibitory kinase Fes phosphorylates mainly the inhibitory motif for CD84. Moreover, Fes, which has been described to become phosphorylated after substrate binding, also gets phosphorylated when coexpressed with CD84. Consistently, Fes was observed to be more phosphorylated after CD84 and FcεRI co-cross-linking. The phosphorylation of the protein phosphatase Src homology region 2 domain-containing phosphatase-1 also increases after CD84 and FcεRI coengagement. Taken together, our results show that CD84 is highly expressed in mast cells and that it contributes to the regulation of FcεRI signaling in SAP- and EAT-2-independent and Fes- and Src homology region 2 domain-containing phosphatase-1-dependent mechanisms.

SLAM family receptors and SAP adaptors in immunity

The signaling lymphocyte activation molecule (SLAM)-associated protein, SAP, was first identified as the protein affected in most cases of X-linked lymphoproliferative (XLP) syndrome, a rare genetic disorder characterized by abnormal responses to Epstein-Barr virus infection, lymphoproliferative syndromes, and dysgammaglobulinemia. SAP consists almost entirely of a single SH2 protein domain that interacts with the cytoplasmic tail of SLAM and related receptors, including 2B4, Ly108, CD84, Ly9, and potentially CRACC. SLAM family members are now recognized as important immunomodulatory receptors with roles in cytotoxicity, humoral immunity, autoimmunity, cell survival, lymphocyte development, and cell adhesion. In this review, we cover recent findings on the roles of SLAM family receptors and the SAP family of adaptors, with a focus on their regulation of the pathways involved in the pathogenesis of XLP and other immune disorders.

Impaired Epstein-Barr virus–specific CD8+ T-cell function in X-linked lymphoproliferative disease is restricted to SLAM family–positive B-cell targets

X-linked lymphoproliferative disease (XLP) is a condition associated with mutations in the signaling lymphocytic activation molecule (SLAM)–associated protein (SAP; SH2D1A). SAP functions as an adaptor, binding to and recruiting signaling molecules to SLAM family receptors expressed on T and natural killer cells. XLP is associated with extreme sensitivity to primary Epstein-Barr virus (EBV) infection, often leading to a lethal infectious mononucleosis. To investigate EBV-specific immunity in XLP patients, we studied 5 individuals who had survived EBV infection and found CD8+ T-cell responses numerically comparable with healthy donors. However, further investigation of in vitro–derived CD8+ T-cell clones established from 2 of these donors showed they efficiently recognized SLAM ligand–negative target cells expressing EBV antigens, but showed impaired recognition of EBV-transformed, SLAM ligand–positive, lymphoblastoid cell lines (LCLs). Importantly, LCL recognition was restored when interactions between the SLAM receptors CD244 and natural killer–, T-, and B-cell antigen (NTBA) and their ligands on LCLs were blocked. We propose that XLP patients' particular sensitivity to EBV, and not to other viruses, reflects at least in part EBV's strict tropism for B lymphocytes and the often inability of the CD8+ T-cell response to contain the primary infection of SLAM ligand–expressing target cells.

Molecular characterization of in vivo adjuvant activity in ferrets vaccinated against influenza virus

The 2009 H1N1 influenza pandemic has prompted a significant need for the development of efficient, single-dose, adjuvanted vaccines. Here we investigated the adjuvant potential of CpG oligodeoxynucleotide (ODN) when used with a human seasonal influenza virus vaccine in ferrets. We found that the CpG ODN-adjuvanted vaccine effectively increased antibody production and activated type I interferon (IFN) responses compared to vaccine alone. Based on these findings, pegylated IFN-alpha2b (PEG-IFN) was also evaluated as an adjuvant in comparison to CpG ODN and complete Freund's adjuvant (CFA). Our results showed that all three vaccines with adjuvant added prevented seasonal human A/Brisbane/59/2007 (H1N1) virus replication more effectively than did vaccine alone. Gene expression profiles indicated that, as well as upregulating IFN-stimulated genes (ISGs), CpG ODN enhanced B-cell activation and increased Toll-like receptor 4 (TLR4) and IFN regulatory factor 4 (IRF4) expression, whereas PEG-IFN augmented adaptive immunity by inducing major histocompatibility complex (MHC) transcription and Ras signaling. In contrast, the use of CFA as an adjuvant induced limited ISG expression but increased the transcription of MHC, cell adhesion molecules, and B-cell activation markers. Taken together, our results better characterize the specific molecular pathways leading to adjuvant activity in different adjuvant-mediated influenza virus vaccinations.

Mouse CD84 is a pan-leukocyte cell-surface molecule that modulates LPS-induced cytokine secretion by macrophages

CD84 is 1 of the 9 SLAM family cell-surface receptors involved in leukocyte activation. The CD84 ectodomain is highly glycosylated, and its cytoplasmic tail contains 2 copies of an ITSM, which can be phosphorylated. Here, we report that although mouse CD84 was present on all BM HSCs, its expression declined in developing thymic and BM lymphocytes. However, CD84 expression levels did increase significantly during the later maturation stages and were expressed abundantly on mature B and T cells. Among lymphocyte subsets, the highest expression was found on innate-like lymphocytes; specifically, on NKT and marginal zone B cells. Splenic CD4+ T(FH) cells exhibited higher levels of CD84 compared with the other CD4+ T cell subsets. CD84 was expressed abundantly on monocytes, macrophages, granulocytes, and DCs. Moreover, as the function of CD84 in myeloid cells remains unknown, we focused on the role this receptor plays in mouse macrophage activation. Transfection of CD84 in RAW-264.7 macrophages led to an increase in MAPK phosphorylation and NF-κB activation upon LPS stimulation. Concomitantly, the presence of CD84 increased the LPS-induced secretion of TNF-α and MCP-1 but lowered IL-10 and IL-6 production significantly. This modulatory effect was mediated by Y(300) within the second ITSM of CD84. Additionally, CD84 knock-down decreased TNF-α and IL-6 production in LPS-activated BMDMs. Taken together, these results show that mouse CD84 is a pan-leukocyte receptor, able to modulate signaling pathways downstream of TLR4, and regulates macrophage cell-fate decisions and effector functions.

Optimal germinal center responses require a multistage T cell:B cell adhesion process involving integrins, SLAM-associated protein, and CD84

CD4(+) T cells deficient in signaling lymphocyte activation molecule (SLAM)-associated protein (SAP) exhibit a selective impairment in adhesion to antigen-presenting B cells but not dendritic cells (DCs), resulting in defective germinal center formation. However, the nature of this selective adhesion defect remained unclear. We found that whereas T cell:DC interactions were primarily integrin dependent, T cell:B cell interactions had both an early integrin-dependent phase and a sustained phase that also required SAP. We further found that the SLAM family member CD84 was required for prolonged T cell:B cell contact, optimal T follicular helper function, and germinal center formation in vivo. Moreover, both CD84 and another SLAM member, Ly108, mediated T cell adhesion and participated in stable T cell:B cell interactions in vitro. Our results reveal insight into the dynamic regulation of T cell:B cell interactions and identify SLAM family members as critical components of sustained T cell:B cell adhesion required for productive humoral immunity.

Human peripheral blood B-cell compartments: a crossroad in B-cell traffic

A relatively high number of different subsets of B-cells are generated through the differentiation of early B-cell precursors into mature B-lymphocytes in the bone marrow (BM) and antigen-triggered maturation of germinal center B-cells into memory B-lymphocytes and plasmablasts in lymphoid tissues. These B-cell subpopulations, which are produced in the BM and lymphoid tissues, recirculate through peripheral blood (PB), into different tissues including mucosa and the BM, where long-living plasma cells produce antibodies. These circulating PB B-cells can be classified according to their maturation stage into i) immature/transitional, ii) naïve, and iii) memory B-lymphocytes, and iv) plasmablasts/plasma cells. Additionally, unique subsets of memory B-lymphocytes and plasmablasts/plasma cells can be identified based on their differential expression of unique Ig-heavy chain isotypes (e.g.: IgM, IgD, IgG, IgA). In the present paper, we review recent data reported in the literature about the distribution, immunophenotypic and functional characteristics of these cell subpopulations, as well as their distribution in PB according to age and seasonal changes. Additional information is also provided in this regard based on the study of a population-based cohort of 600 healthy adults aged from 20 to 80 years, recruited in the Salamanca area in western Spain. Detailed knowledge of the distribution and traffic of B-cell subsets through PB mirrors the immune status of an individual subject and it may also contribute to a better understanding of B-cell disorders related to B-cell biology and homeostasis, such as monoclonal B-cell lymphocytosis (MBL).

Restimulation-induced apoptosis of T cells is impaired in patients with X-linked lymphoproliferative disease caused by SAP deficiency

X-linked lymphoproliferative disease (XLP) is a rare congenital immunodeficiency that leads to an extreme, usually fatal increase in the number of lymphocytes upon infection with EBV. It is most commonly defined molecularly by loss of expression of SLAM-associated protein (SAP). Despite this, there is little understanding of how SAP deficiency causes lymphocytosis following EBV infection. Here we show that T cells from individuals with XLP are specifically resistant to apoptosis mediated by TCR restimulation, a process that normally constrains T cell expansion during immune responses. Expression of SAP and the SLAM family receptor NK, T, and B cell antigen (NTB-A) were required for TCR-induced upregulation of key pro-apoptotic molecules and subsequent apoptosis. Further, SAP/NTB-A signaling augmented the strength of the proximal TCR signal to achieve the threshold required for restimulation-induced cell death (RICD). Strikingly, TCR ligation in activated T cells triggered increased recruitment of SAP to NTB-A, dissociation of the phosphatase SHP-1, and colocalization of NTB-A with CD3 aggregates. In contrast, NTB-A and SHP-1 contributed to RICD resistance in XLP T cells. Our results reveal what we believe to be novel roles for NTB-A and SAP in regulating T cell homeostasis through apoptosis and provide mechanistic insight into the pathogenesis of lymphoproliferative disease in XLP.

The SLAM and SAP gene families control innate and adaptive immune responses

The nine SLAM-family genes, SLAMF1-9, a subfamily of the immunoglobulin superfamily, encode differentially expressed cell-surface receptors of hematopoietic cells. Engagement with their ligands, which are predominantly homotypic, leads to distinct signal transduction events, for instance those that occur in the T or NK cell immune synapse. Upon phosphorylation of one or more copies of a unique tyrosine-based signaling motif in their cytoplasmic tails, six of the SLAM receptors recruit the highly specific single SH2-domain adapters SLAM-associated protein (SAP), EAT-2A, and/or EAT-2B. These adapters in turn bind to the tyrosine kinase Fyn and/or other protein tyrosine kinases connecting the receptors to signal transduction networks. Individuals deficient in the SAP gene, SH2D1A, develop an immunodeficiency syndrome: X-linked lympho-proliferative disease. In addition to operating in the immune synapse, SLAM receptors initiate or partake in multiple effector functions of hematopoietic cells, for example, neutrophil and macrophage killing and platelet aggregation. Here we discuss the current understanding of the structure and function of these recently discovered receptors and adapter molecules in the regulation of adaptive and innate immune responses.

Gene expression analyses in Atlantic salmon challenged with infectious salmon anemia virus reveal differences between individuals with early, intermediate and late mortality

BACKGROUND

Infectious salmon anemia virus (ISAV) causes a multisystemic disease responsible for severe losses in salmon aquaculture. Better understanding of factors that explain variations in resistance between individuals and families is essential for development of strategies for disease control. To approach this, we compared global gene expression using microarrays in fish dying early and late in the time course following infection from a highly pathogenic ISAV.

RESULTS

Tissues (gill, heart, liver and spleen) from infected Atlantic salmon (cohabitation, ISAV Glesvaer 2/90 isolate) were collected from three stages over the time course of the experiment; early (EM, 0-10% cumulative mortality (CM), 21-25 days post-infection (DPI)), intermediate (IM, 35-55% CM, 28-31 DPI) and late (LM, 75-85% CM, 37-48 DPI) mortality. Viral loads were equal in EM and IM but dropped markedly in LM fish. Gene expression analyses using a 1.8 K salmonid fish cDNA microarray (SFA2.0) and real-time qPCR revealed a large group of genes highly up-regulated across tissues in EM, which were mainly implicated in innate antiviral responses and cellular stress. Despite equal levels of MHC class I in EM and LM, increase of splenic and cardiac expression of immunoglobulin-like genes was found only in LM while a suite of adaptive immunity markers were activated already in IM. The hepatic responses to ISAV were characterized by difference between EM and LM in expression of chaperones and genes involved in eicosanoid metabolism. To develop classification of high and low resistance phenotypes based on a small number of genes, we processed results from qPCR analyses of liver using a linear discriminant analysis. Four genes (5-lipoxygenase activating protein, cytochrome P450 2K4-1, galectin-9 and annexin A1) were sufficient for correct assignment of individuals to EM, LM and uninfected groups, while IM was inseparable from EM. Three of four prognostic markers are involved in metabolism of inflammatory regulators.

CONCLUSION

This study adds to the understanding of molecular determinants for resistance to acute ISAV infection. The most susceptible individuals were characterized by high viral replication and dramatic activation of innate immune responses, which did not provide protection. The ability to endure high levels of infection for sustained periods could be associated with lower inflammatory responses while subsequent protection and viral clearance was most likely conferred by activation of adaptive immunity.

Inappropriate recruitment and activity by the Src homology region 2 domain-containing phosphatase 1 (SHP1) is responsible for receptor dominance in the SHIP-deficient NK cell

We have previously demonstrated that the NKR repertoire is profoundly disrupted by SHIP deficiency. This repertoire disruption is characterized by receptor dominance where inhibitory signals from 2B4 repress killing of complex targets expressing MHC class I and activating ligands. In this study, we examine the molecular basis of receptor dominance in SHIP-/- NK cells. In this study, we show that in SHIP-/- NK cells there is a pronounced bias toward the 2B4 long isoform. We have also characterized signaling molecules recruited to 2B4 in SHIP-/- NK cells. Interestingly, we find that approximately 10- to 16-fold more Src homology region 2 domain-containing phosphatase 1 (SHP1) is recruited to 2B4 in SHIP-/- NK cells when compared with wild type. Consistent with SHP1 overrecruitment, treatment with sodium orthovanadate or a novel inhibitor with micromolar activity against SHP1 restores the ability of SHIP-/- NK cells to kill Rae1+ RMA and M157+ targets. These findings define the molecular basis for hyporesponsiveness by SHIP-deficient NK cells.

Regulation of cellular and humoral immune responses by the SLAM and SAP families of molecules

SAP (SLAM-associated protein) was identified in 1998 as an adaptor molecule involved in the intracellular signaling pathways elicited through the cell surface receptor SLAM and as the protein defective in the human immunodeficiency X-linked lymphoproliferative disease (XLP). During the past eight years, it has been established that the SLAM family of cell surface receptors (SLAM, 2B4, NTB-A, Ly9, CD84) and the SAP family of adaptors (SAP, EAT-2, ERT) play critical roles in lymphocyte development, differentiation, and acquisition of effector functions. Studies of these proteins have shown unexpected roles in cytokine production by T cells and myeloid cells, T cell-dependent humoral immune responses, NK cell-mediated cytotoxicity, and NKT cell development. This review highlights recent findings that have improved our understanding of the roles of the SLAM and SAP families of molecules in immune regulation and discusses how perturbations in the signaling pathways involving these proteins can result in different disease states.

The role of SLAM family receptors in immune cell signaling

The signaling lymphocyte-activating molecule (SLAM) family immunoreceptors are expressed in a wide array of immune cells, including both T and B lymphocytes. By virtue of their ability to transduce tyrosine phosphorylation signals through the so-called ITSM (immunoreceptor tyrosine-based switch motif) sequences, they play an important part in regulating both innate and adaptive immune responses. The critical role of the SLAM immunoreceptors in mediating normal immune reactions was highlighted in recent findings that SAP, a SLAM-associated protein, modulates the activities of various immune cells through interactions with different members of the SLAM family expressed in these cells. Importantly, mutations or deletions of the sap gene in humans result in the X-linked lymphoproliferative syndrome. In this review, we summarize current knowledge and survey the latest developments in signal transduction events triggered by the activation of SLAM family receptors in different cell types.

Molecular Analysis of NTB-A Signaling: A Role for EAT-2 in NTB-A-Mediated Activation of Human NK Cells

Engagement of NTB-A on human NK cells by homophilic interaction with NTB-A-expressing target cells can trigger NK cell cytotoxicity, cytokine production, and proliferation. To better understand how NTB-A can activate NK cells, we analyzed the molecular mechanisms of NTB-A signaling. We show that NTB-A is tyrosine phosphorylated in unstimulated human NK cells and associates with SLAM-associated protein (SAP) and EAT-2. This phosphorylation of NTB-A is mediated by Src family kinases and is most likely a result of the homophilic interaction of NTB-A among neighboring NK cells. Stimulation of NK cells by NTB-A-positive targets results in increased NTB-A phosphorylation. The cytoplasmic tail of NTB-A contains three tyrosines, two of which are embedded within an immunoreceptor tyrosine-based switch motif. We generated a NTB-A-negative NK cell line, in which we expressed different mutants of NTB-A. Functional studies showed that the second tyrosine is sufficient and essential for NTB-A-mediated cytotoxicity. EAT-2, but not SAP, is recruited to this second tyrosine, indicating that SAP may be dispensable for this NTB-A function. To further investigate this, we silenced SAP expression in NK cell lines. Functional analysis of these cells showed that NTB-A can mediate NK cell cytotoxicity in the absence of SAP, probably via EAT-2. In contrast, NTB-A-mediated IFN-gamma production was greatly reduced in the absence of SAP, demonstrating that cytokine production and cytotoxicity are differentially dependent on SAP and possibly EAT-2.

Cutting edge: dominance by an MHC-independent inhibitory receptor compromises NK killing of complex targets

Inhibitory receptors that recognize MHC class I molecules regulate NK cell responses and self-tolerance. Recent evidence indicates that self-ligands not present in the MHC locus also can modulate NK function. In this study, we show that an inhibitory receptor that recognizes an MHC-independent ligand is over expressed in SHIP(-/-) mice at all stages of NK development and differentiation. Overexpression of this receptor compromises key cytolytic NK functions, including killing of allogeneic, tumor, and viral targets. These results further demonstrate the critical role that SHIP plays in regulation of the NK receptor repertoire and show that regulation of MHC-independent inhibitory receptors is crucial for NK recognition and cytolysis of complex targets.

Missense mutations in SH2D1A identified in patients with X-linked lymphoproliferative disease differentially affect the expression and function of SAP

X-linked lymphoproliferative disease (XLP) is an immunodeficiency resulting from mutations in SH2D1A, which encodes signalling lymphocytic activation molecule (SLAM)-associated protein (SAP). In addition to SLAM, SAP associates with several other cell-surface receptors including 2B4 (CD244), Ly9 (CD229), CD84 and NTB-A. SAP contains a single src-homology-2 domain and acts as an intracellular adaptor protein by recruiting the protein tyrosine kinase FynT to the cytoplasmic domains of some of these receptors, which results in the initiation of specific downstream signal transduction pathways. XLP is likely to result from perturbed signalling through one or more of these SAP-associating receptors. In this study, we identified missense (Y54C, I84T and F87S) and insertion (fs82 --> X103) mutations in four different kindreds affected by XLP. Each mutation dramatically reduced the half-life of SAP, thus diminishing its expression in primary lymphocytes as well as in transfected cell lines. Interestingly, although the Y54C and F87S mutations compromised the ability of SAP to associate with different receptors, the I84T mutation had no effect on the ability of SAP to bind SLAM, CD84 or 2B4. However, signalling downstream of SLAM was reduced in the presence of SAP bearing the I84T mutation. These findings indicate that, irrespective of the type of mutation, signalling through SAP-associating receptors in XLP can be impaired by reducing the expression of SAP, the ability of SAP to bind surface receptors and/or its ability to activate signal transduction downstream of the SLAM-SAP complex.

The cytotoxicity receptor CRACC (CS-1) recruits EAT-2 and activates the PI3K and phospholipase Cgamma signaling pathways in human NK cells

The CD2-like receptor-activating cytotoxic cell (CRACC) is a cell surface receptor of the CD2 family that triggers NK cell-mediated cytotoxicity through an undefined signaling pathway. CRACC contains cytoplasmic tyrosine-based motifs, immunoreceptor tyrosine-based switch motifs, which resemble those found in the NK cell receptor 2B4. In 2B4, these motifs recruit the adaptor signaling lymphocytic activation molecule-associated protein (SAP), which initiates a signaling cascade mediating cytotoxicity. However, CRACC does not recruit SAP. In this study, we demonstrate that, upon activation, CRACC associates with a homolog of SAP, Ewing's sarcoma's/FLI1-activated transcript 2 (EAT-2), in human NK cells. We show that association of EAT-2 induces the phosphorylation of CRACC and that this process is partially reduced by a pharmacological inhibitor of Src kinases. We identify PLCgamma1, PLCgamma2, and PI3K as the major signaling mediators downstream of CRACC/EAT-2 implicated in NK cell-mediated cytotoxicity. Moreover, EAT-2 also associates with 2B4 predominantly in resting NK cells, whereas SAP preferentially binds 2B4 upon activation. These results outline a new signaling pathway that triggers CRACC-mediated cytotoxicity and modulates 2B4-mediated activation.

Immune regulation by SLAM family receptors and SAP-related adaptors

The signalling lymphocytic activation molecule (SLAM) family of receptors is expressed by a wide range of immune cells. Through their cytoplasmic domain, SLAM family receptors associate with SLAM-associated protein (SAP)-related molecules, a group of cytoplasmic adaptors composed almost exclusively of an SRC homology 2 domain. SAP, the prototype of the SAP family, is mutated in a human immunodeficiency named X-linked lymphoproliferative (XLP) disease. Recent observations indicate that SLAM family receptors, in association with SAP family adaptors, have crucial roles during normal immune reactions in innate and adaptive immune cells. The latest progress in this field is reviewed here.

Genomic view of systemic autoimmunity in MRLlpr mice

MRLlpr mice develop spontaneous systemic autoimmunity with many hallmarks of the human disease systemic lupus erythematosus. Although a variety of genes have been implicated in this model, disease pathogenesis is still poorly understood. In an effort to identify novel genes and pathways, we performed genome-wide mRNA expression analysis in the spleens and kidneys of MRLlpr mice throughout the disease course. Samples were collected from cohorts of C57BL/6, MRL+/+ and MRLlpr mice, and profiled by flow cytometry and gene expression microarrays. Serum autoantibodies and renal pathology were studied in parallel. We identified 236 genes in MRLlpr spleen that showed significant threefold or greater changes in expression between 6 and 20 weeks. Of interest, a number of interferon-responsive genes were expressed early, and remained dysregulated throughout the disease course. Many chemokines, cell surface proteins, transcription factors and cytokines, including IFN-gamma, also showed altered expression as disease progressed. Analysis of kidneys indicated the presence of severe inflammation that coincided with evidence for changes in kidney function and elevated expression of IFN-inducible genes, complement components and antigen presentation genes. These data provide a unique genomic view of the progression to fatal autoimmunity in MRLlpr mice, and provide new candidate genes and pathways to explore.

Novel targets for antithrombotic drug discovery

Platelet aggregation is a dynamic entity, capable of directing its own growth and stability via the activation of signaling cascades that lead to the expression and secretion of various secondary agonists. Recent data using proteomics and genomics strategies have established that signaling pathways during platelet aggregation are triggered by two homophilic adhesion molecules, CD84 and CD150 (SLAM), and by a novel EGF-containing receptor, PEAR1, which are tyrosine-phosphorylated in a platelet-aggregation-dependent fashion (N. Nanda, P. Andre, M. Bao et al., Platelet aggregation induces platelet aggregate stability via SLAM family receptor signaling, Blood 106 (2005) 3028-3034, N. Nanda, M. Bao, H. Lin et al., Platelet Endothelial Aggregation Receptor 1 (PEAR1), a novel epidermal growth factor repeat-containing transmembrane receptor, participates in platelet contact-induced activation, J. Biol. Chem. 280 (2005) 24680-24689). Analysis of SLAM-deficient mice revealed an overall defect in platelet aggregation in vitro and a delayed arterial thrombotic process in vivo. The data indicate that these aggregation co-receptors may function in a "platelet synapse" and may be novel targets for antithrombotic drug discovery.

The CD2 family of natural killer cell receptors

The CD2 family of receptors is evolutionarily conserved and widely expressed on cells within the hematopoietic compartment. In recent years several new members have been identified with important roles in the immune system. CD2 family members regulate natural killer (NK) cell lytic activity and inflammatory cytokine production when engaged by ligands on tumor cells. Furthermore, a subfamily of CD2 receptors, the CD 150-like molecules, has been implicated in the pathogenesis of X-linked lymphoproliferative disease (XLP). Many of these receptors have now been shown to bind homophilically or heterophilically to other molecules within the family. With these discoveries a novel mechanism for lymphocyte regulation has emerged: CD2 family members on NK cells engage ligands on neighboring NK cells, leading to NK cell stimulation. Moreover, heterotypic stimulatory interactions between NK cells and other leukocytes also occur. In this manner, CD2 family members may provide interlymphocyte communication that maintains organization within the hematopoietic compartment and amplifies immune responses. This review discusses these multiple roles for CD2 family members, focusing specifically on the regulation of NK cells.

Selective generation of functional somatically mutated IgM+CD27+, but not Ig isotype-switched, memory B cells in X-linked lymphoproliferative disease

Individuals with X-linked lymphoproliferative disease (XLP) display defects in B cell differentiation in vivo. Specifically, XLP patients do not generate a normal number of CD27 memory B cells, and those few that are present are IgM. Recent studies have suggested that IgMCD27 B cells are not true memory cells, but rather B cells that guard against T cell-independent pathogens. Here we show that human XLP IgMCD27 B cells resemble normal memory B cells both morphologically and phenotypically. Additionally, IgMCD27 B cells exhibited functional characteristics of normal memory B cells, including the ability to secrete more Ig than naive B cells in response to both T cell-dependent and -independent stimuli. Analysis of spleens from XLP patients revealed a paucity of germinal centers (GCs), and the rare GCs detected were poorly formed. Despite this, Ig variable region genes expressed by XLP IgMCD27 B cells had undergone somatic hypermutation to an extent comparable to that of normal memory B cells. These findings reveal a differential requirement for the generation of IgM and Ig isotype-switched memory B cells, with the latter only being generated by fully formed GCs. Production of affinity-matured IgM by IgMCD27 B cells may protect against pathogens to which a normal immune response is elicited in XLP patients.

Genomic and Expression Profiling of Human Spermatocytic Seminomas: Primary Spermatocyte as Tumorigenic Precursor and DMRT1 as Candidate Chromosome 9 Gene

Spermatocytic seminomas are solid tumors found solely in the testis of predominantly elderly individuals. We investigated these tumors using a genome-wide analysis for structural and numerical chromosomal changes through conventional karyotyping, spectral karyotyping, and array comparative genomic hybridization using a 32 K genomic tiling-path resolution BAC platform (confirmed by in situ hybridization). Our panel of five spermatocytic seminomas showed a specific pattern of chromosomal imbalances, mainly numerical in nature (range, 3-24 per tumor). Gain of chromosome 9 was the only consistent anomaly, which in one case also involved amplification of the 9p21.3-pter region. Parallel chromosome level expression profiling as well as microarray expression analyses (Affymetrix U133 plus 2.0) was also done. Unsupervised cluster analysis showed that a profile containing transcriptional data on 373 genes (difference of > or = 3.0-fold) is suitable for distinguishing these tumors from seminomas/dysgerminomas. The diagnostic markers SSX2-4 and POU5F1 (OCT3/OCT4), previously identified by us, were among the top discriminatory genes, thereby validating the experimental set-up. In addition, novel discriminatory markers suitable for diagnostic purposes were identified, including Deleted in Azospermia (DAZ). Although the seminomas/dysgerminomas were characterized by expression of stem cell-specific genes (e.g., POU5F1, PROM1/CD133, and ZFP42), spermatocytic seminomas expressed multiple cancer testis antigens, including TSP50 and CTCFL (BORIS), as well as genes known to be expressed specifically during prophase meiosis I (TCFL5, CLGN, and LDHc). This is consistent with different cells of origin, the primordial germ cell and primary spermatocyte, respectively. Based on the region of amplification defined on 9p and the associated expression plus confirmatory immunohistochemistry, DMRT1 (a male-specific transcriptional regulator) was identified as a likely candidate gene for involvement in the development of spermatocytic seminomas.

Fine-tuning of immune responses by SLAM-related receptors

The modulation of antigen receptor signals is important for a productive immune response. The main function of the recently identified members of the signaling lymphocyte activating molecule (SLAM)-related receptors (SRR) is the fine-tuning of immune cell activation. Disruption of SRR function is the cause for severe immune disorders such as X-linked lymphoproliferative syndrome (XLP), where XLP patients carry a mutation in SLAM-associated protein (SAP) (SH2D1A), an important adaptor molecule for the signal transduction of SRR. Recent data also suggest that SRR may play a role in autoimmune diseases and the function of hematopoietic stem and progenitor cells. Here, we review the current understanding of SRR function in different immune cells.

Vitamin A and immune function: retinoic acid modulates population dynamics in antigen receptor and CD38-stimulated splenic B cells

Vitamin A and its active metabolite, all-trans retinoic acid (RA), regulate the antibody response in vivo, although the underlying mechanisms are not well understood. We have investigated the regulation by RA of B cell population dynamics and Ig gene expression in purified splenic mouse B cells stimulated through the B cell antigen receptor (BCR) and/or CD38, a BCR coreceptor. After ligation of the BCR and/or CD38, B cells became more heterogeneous in size. RA substantially restrained this change, concomitant with inhibition of cell proliferation. To examine B cell heterogeneity more closely, we categorized stimulated B cells by size (forward angle light scatter) and determined cell division dynamics, germ-line Ig heavy chain gene transcription and surface IgG1 (sIgG1) expression. Flow cytometric analysis of carboxyfluorescein diacetate succinimidyl ester-labeled B cells costained for sIgG1 showed that the more proliferative groups of B cells were smaller, whereas cells expressing more sIgG1 were larger. RA enriched the latter population, whereas cell division frequency in general and the number of smaller B cells that had undergone division cycles were reduced. Although RA significantly inhibited Ig germ-line transcript levels in the total B cell population, CD19(-)IgG1(+) B cells, which represent a more differentiated phenotype, were enriched. Furthermore, pax-5 mRNA was decreased and activation-induced cytidine deaminase mRNA was increased in RA-treated stimulated B cells. Thus, RA regulated factors known to be required for Ig class switch recombination and modulated the population dynamics of ligation-stimulated B cells, while promoting the progression of a fraction of B cells into differentiated sIgG-expressing cells.

An epistatic effect of the female specific loci on the development of autoimmune vasculitis and antinuclear autoantibody in murine lupus

OBJECTIVE

To identify the genetic loci regulating the incidence and severity of renal autoimmune vasculitis developed in murine lupus.

METHODS

Vasculitis of renal arteries was histopathologically evaluated in MRL/Mp-Fas(lpr) (MRL/lpr), C57BL/6-Fas(lpr) (B6/lpr), (MRL/lpr x B6/lpr) F1, and MRL/lpr x (MRL/lpr x B6/lpr) F1 backcross mice. Using genomic DNA samples of the backcross mice, genome-wide scans, association studies, and linkage analyses were carried out based on genotypes of polymorphic microsatellite markers. Correlations of vasculitis grade and levels of various autoantibodies were also evaluated.

RESULTS

Two recessive susceptibility loci of the MRL allele were identified on chromosomes 4 and 1, which had previously been defined as the autoimmune related loci termed Arvm1 and Sle-1/Nba2, respectively. The former was epistatic to the latter in a female specific manner. The titre of antinuclear autoantibody (ANA) in IgG class, but not ANA in IgM class or anti-dsDNA in either IgG or IgM class, correlated significantly with vasculitis grade.

CONCLUSIONS

The present loci have been reported in previous studies using a different set of murine strains, suggesting that they are of importance in the development of autoimmune vasculitis in murine models. The concomitance of autoimmune vasculitis and IgG ANA suggests a shared genetic factor regulating these traits.

Platelet aggregation induces platelet aggregate stability via SLAM family receptor signaling

Platelet aggregation is a dynamic entity, capable of directing its own growth and stability via the activation of signaling cascades that lead to the expression and secretion of various secondary agonists. Here we show that the signaling pathways triggered during platelet aggregation include an intrinsic pro-thrombotic activity mediated by 2 homophilic adhesion molecules, CD84 and CD150 (SLAM [signaling lymphocyte activation molecule]), which are tyrosine phosphorylated in a platelet aggregation-dependent fashion. The 2 CD84/SLAM adapter proteins, SAP (SLAM-associated protein) and EAT-2 (EWS-activated transcript-2), were found in platelets; only SAP, however, was found to immunoprecipitate with tyrosine-phosphorylated SLAM. The immobilized extracellular domain of CD84 promoted microaggregate formation, while SAP-deficient platelets demonstrated defective spreading on immobilized CD84, demonstrating a functional role in platelets for SLAM family interactions. Finally, analysis of SLAM-deficient mice revealed an overall defect in platelet aggregation in vitro and a delayed arterial thrombotic process in vivo. The data indicate that signaling of the adhesion molecules in the SLAM family, activated by proximity during aggregation, further stabilize platelet-platelet interactions in thrombosis.

Molecular and cellular pathogenesis of X-linked lymphoproliferative disease

X-linked lymphoproliferative disease (XLP) is an inherited immune defect caused by mutations in the Src homology 2 domain-containing gene 1A, which encodes the adapter protein, signaling lymphocytic activation molecule (SLAM)-associated protein (SAP). SAP is expressed in T cells, natural killer (NK) cells, and NKT cells, where it binds to the cytoplasmic domain of the surface receptor SLAM (CD150) and the related receptors, 2B4 (CD244), CD84, Ly9 (CD229), NK-T-B-antigen, and CD2-like receptor-activating cytotoxic T cells. SAP also binds to the Src family tyrosine kinase Fyn and recruits it to SLAM, which leads to the generation of downstream phosphotyrosine signals. While the roles of the SLAM family receptors are only beginning to be understood, experiments suggest that these molecules regulate important aspects of lymphocyte function, such as proliferation, cytokine secretion, cytotoxicity, and antibody production. Thus, in XLP patients who lack functional SAP, the SLAM family receptors may not signal properly. This property likely contributes to the phenotypes of XLP, including fulminant infectious mononucleosis, lymphoma, and hypogammaglobulinemia. Further studies of SAP and the SLAM family receptors will provide insights into XLP and elucidate the signaling events regulating lymphocyte ontogeny and function.

Gene Expression Profiling of 17β-Estradiol and Genistein Effects on Mouse Thymus

Estrogen regulates thymic development and involution and modulates immune function. Despite its critical role in thymus, as well as in autoimmune disorders, the mechanism by which estrogen affects the thymus is not well understood. We previously reported that the estrogenic soy isoflavone genistein, as well as 17beta-estradiol (E2), could induce thymic involution, but genistein effects were only partially mediated through estrogen receptors. To provide insights into mechanisms of estrogenic effects in the thymus, we investigated thymic gene expression changes induced by E2 (125 ng/day) and genistein (1500 ppm in feed) in weanling mice using high-density DNA arrays. We identified several E2-responsive genes involved in thymic development and thymocyte signaling during selection and maturation. Functional characterization indicated effects on genes involved in transcription, apoptosis, and the cell cycle. This study also identified changes in several E2-regulated transcripts essential to maintain immune self-tolerance. E2 upregulated more genes than genistein, while genistein downregulated more genes than E2. Though each treatment regulated several genes not altered by the other, there was considerable overlap in the genes regulated by E2 and genistein. Changes in transcription factors and cell cycle factors were consistent with decreases in cell proliferation induced by both genistein and E2. As indicated by the regulation of non-E2-responsive genes, genistein also induced unique effects through non-estrogenic mechanisms. The specific downregulation of the CD4 coreceptor transcript by genistein was consistent with the decline of CD4+ thymocytes in genistein-treated mice in our previous study. This is the first study identifying E2 and genistein target genes in the thymus. These findings provide new mechanistic insights toward explaining estrogen action on thymocyte development, selection, and maturation, as well as the effects of genistein on prenatal and neonatal thymic development and function.

Impaired humoral immunity in X-linked lymphoproliferative disease is associated with defective IL-10 production by CD4+ T cells

X-linked lymphoproliferative disease (XLP) is an often-fatal immunodeficiency characterized by hypogammaglobulinemia, fulminant infectious mononucleosis, and/or lymphoma. The genetic lesion in XLP, SH2D1A, encodes the adaptor protein SAP (signaling lymphocytic activation molecule-associated [SLAM-associated] protein); however, the mechanism(s) by which mutations in SH2D1A causes hypogammaglobulinemia is unknown. Our analysis of 14 XLP patients revealed normal B cell development but a marked reduction in the number of memory B cells. The few memory cells detected were IgM(+), revealing deficient isotype switching in vivo. However, XLP B cells underwent proliferation and differentiation in vitro as efficiently as control B cells, which indicates that the block in differentiation in vivo is B cell extrinsic. This possibility is supported by the finding that XLP CD4(+) T cells did not efficiently differentiate into IL-10(+) effector cells or provide optimal B cell help in vitro. Importantly, the B cell help provided by SAP-deficient CD4(+) T cells was improved by provision of exogenous IL-10 or ectopic expression of SAP, which resulted in increased IL-10 production by T cells. XLP CD4(+) T cells also failed to efficiently upregulate expression of inducible costimulator (ICOS), a potent inducer of IL-10 production by CD4(+) T cells. Thus, insufficient IL-10 production may contribute to hypogammaglobulinemia in XLP. This finding suggests new strategies for treating this immunodeficiency.

SAP controls the cytolytic activity of CD8+ T cells against EBV-infected cells

The adaptor protein SAP regulates signaling through signaling lymphocytic activation molecule (SLAM)-family receptors expressed on T and natural killer (NK) cells. In patients affected by X-linked lymphoproliferative (XLP) disease, mutations in the SH2D1A gene result in defective lytic activity. However, the mechanism by which SAP controls cytotoxic activity remains unclear. T-cell-receptor (TCR) activation of CD8(+) cytotoxic T cells (CTLs) results in down-regulation of SAP, suggesting that this protein is involved in early activation events. Here, we show that SAP-deficient CTLs from patients with XLP and hemophagocytic lymphohistiocytosis (HLH) display a specific lytic defect against autologous and allogeneic Epstein-Barr virus (EBV)-positive B cells. This defect is associated with the defective polarization of 2B4, perforin, and lipid rafts at the contact area of CTLs with EBV-positive targets. Blockade of 2B4 in normal CTLs reproduces the defects in lysis and polarization observed in SAP-deficient CTLs. Expression and regulation of the SLAM-family receptors SLAM, CD84, and 2B4, as well as the lytic effectors perforin and granzyme-B are normal in SAP-deficient CTLs. In addition, TCR stimulation leads to normal proliferation and production of interleukin 2 (IL-2), IL-4, and interferon-gamma (IFN-gamma). These results demonstrate that the SAP/2B4 pathway plays a key role in CTL lytic activity against EBV-positive targets by promoting the polarization of the lytic machinery.