Targeting the tetraspanin CD81 blocks monocyte transmigration and ameliorates EAE

Mice with type I interferon signaling deficiency are prone to epilepsy upon HSV-1 infection

Viral encephalitis continues to be a significant public health concern. In our previous study, we discovered a lower expression of antiviral factors, such as IFN-β, STING and IFI16, in the brain tissues of patients with Rasmussen's encephalitis (RE), a rare chronic neurological disorder often occurred in children, characterized by unihemispheric brain atrophy. Furthermore, a higher cumulative viral score of human herpes viruses (HHVs) was also found to have a significant positive correlation with the unihemispheric atrophy in RE. Type I IFNs (IFN-I) signaling is essential for innate anti-infection response by binding to IFN-α/β receptor (IFNAR). In this study, we infected WT mice and IFNAR-deficient A6 mice with herpes simplex virus 1 (HSV-1) via periocular injection to investigate the relationship between IFN-I signaling and HHVs-induced brain lesions. While all mice exhibited typical viral encephalitis lesions in their brains, HSV-induced epilepsy was only observed in A6 mice. The gene expression matrix, functional enrichment analysis and protein-protein interaction network revealed four gene models that were positively related with HSV-induced epilepsy. Additionally, ten key genes with the highest scores were identified. Taken together, these findings indicate that intact IFN-I signaling can effectively limit HHVs induced neural symptoms and brain lesions, thereby confirming the positive correlation between IFN-I signaling repression and brain atrophy in RE and other HHVs encephalitis.

The Potential Role of Inflammation in Modulating Endogenous Hippocampal Neurogenesis After Spinal Cord Injury

Currently there are approximately 291,000 people suffering from a spinal cord injury (SCI) in the United States. SCI is associated with traumatic changes in mobility and neuralgia, as well as many other long-term chronic health complications, including metabolic disorders, diabetes mellitus, non-alcoholic steatohepatitis, osteoporosis, and elevated inflammatory markers. Due to medical advances, patients with SCI survive much longer than previously. This increase in life expectancy exposes them to novel neurological complications such as memory loss, cognitive decline, depression, and Alzheimer's disease. In fact, these usually age-associated disorders are more prevalent in people living with SCI. A common factor of these disorders is the reduction in hippocampal neurogenesis. Inflammation, which is elevated after SCI, plays a major role in modulating hippocampal neurogenesis. While there is no clear consensus on the mechanism of the decline in hippocampal neurogenesis and cognition after SCI, we will examine in this review how SCI-induced inflammation could modulate hippocampal neurogenesis and provoke age-associated neurological disorders. Thereafter, we will discuss possible therapeutic options which may mitigate the influence of SCI associated complications on hippocampal neurogenesis.

A monoclonal antibody recognizing a new epitope on CD81 inhibits T-cell migration without inducing cytokine production

CD81 is involved in leukocyte migration and cytokine induction. Previous work found that anti-CD81 monoclonal antibodies (mAbs) showed therapeutic potential for several immune diseases via inhibiting leukocyte migration. Although the suppression of cell migration is a promising approach for treating immune diseases, some anti-CD81 mAbs can induce cytokine production, which may exacerbate disease. To obtain new anti-human CD81 mAbs that inhibited migration in the absence of cytokine production enhancement activity, we screened a human single chain variable fragment by phage library. One of the new anti-CD81 mAbs isolated, DSP-8250, had equivalent inhibitory cell migration activity with the established anti-CD81 mAb 5A6, but it lacked cytokine induction activity. These mAbs recognized different epitopes on CD81. mAb 5A6, which had inhibitory activity on T-cell migration and increased cytokine production, bound to three residues, Ser179, Asn180 and Phe186 of CD81. In contrast, DSP-8250, which had inhibitory activity on T-cell migration but no cytokine enhancement activity, bound to four residues, His151, Ala164, Ser168 and Asn172 of CD81 as a unique epitope. These results indicate that the set of His151, Ala164, Ser168 and Asn172 forms a novel epitope that might make the application of anti-CD81 mAb therapeutically useful.

Membrane Compartmentalization and Scaffold Proteins in Leukocyte Migration

Leukocyte migration across vessels into and within peripheral and lymphoid tissues is essential for host defense against invading pathogens. Leukocytes are specialized in sensing a variety of guidance cues and to integrate environmental stimuli to navigate in a timely and spatially controlled manner. These extracellular signals must be transmitted across the leukocyte’s plasma membrane in a way that intracellular signaling cascades enable directional cell movement. Therefore, the composition of the membrane in concert with proteins that influence the compartmentalization of the plasma membrane or contribute to delineate intracellular signaling molecules are key in controlling leukocyte navigation. This becomes evident by the fact that mislocalization of membrane proteins is known to deleteriously affect cellular functions that may cause diseases. In this review we summarize recent advances made in the understanding of how membrane cholesterol levels modulate chemokine receptor signaling and hence leukocyte trafficking. Moreover, we provide an overview on the role of membrane scaffold proteins, particularly tetraspanins, flotillins/reggies, and caveolins in controlling leukocyte migration both in vitro and in vivo.

Anti-CD81 antibodies reduce migration of activated T lymphocytes and attenuate mouse experimental colitis

Inflammatory bowel disease (IBD) is an immunological disease associated with CD4⁺ T cell activation in the intestines. CD81 is a regulator of the immune system with multiple biological functions. Therefore, in this study, we assessed the contribution of CD81 to IBD pathophysiology and the therapeutic efficacy of anti-CD81 antibodies. Expression of CD81 was increased on activated T cells in vitro and in colitic mice in vivo. Therapeutic effects of anti-CD81 antibodies on colitic symptoms and inflammation were evaluated in mice with colitis, including long-term effects of the antibodies. Treatment with anti-CD81 antibodies improved colitis scores, reduced colon shortening, decreased loss of body weight, and resulted in fewer pathological changes of the colon in colitic mice. Moreover, the increased inflammatory markers in the blood of colitic mice were decreased by anti-CD81 antibodies. The anti-CD81 antibody treatment had long-lasting therapeutic effects on colitic mice, even after cessation of treatment. Two different clones of the anti-mouse CD81 antibody were also effective in mice with colitis. Furthermore, anti-CD81 antibodies reduced migration of CD4⁺ T cells both in colitic mice and in vitro. Thus, CD81 contributes to IBD pathology and treatment with anti-CD81 antibodies may be a potential novel therapy for IBD patients.

Modulation of Tetraspanin 32 (TSPAN32) Expression in T Cell-Mediated Immune Responses and in Multiple Sclerosis

Tetraspanins are a conserved family of proteins involved in a number of biological processes including, cell–cell interactions, fertility, cancer metastasis and immune responses. It has previously been shown that TSPAN32 knockout mice have normal hemopoiesis and B-cell responses, but hyperproliferative T cells. Here, we show that TSPAN32 is expressed at higher levels in the lymphoid lineage as compared to myeloid cells. In vitro activation of T helper cells via anti-CD3/CD28 is associated with a significant downregulation of TSPAN32. Interestingly, engagement of CD3 is sufficient to modulate TSPAN32 expression, and its effect is potentiated by costimulation with anti-CD28, but not anti-CTLA4, -ICOS nor -PD1. Accordingly, we measured the transcriptomic levels of TSPAN32 in polarized T cells under Th1 and Th2 conditions and TSPAN32 resulted significantly reduced as compared with unstimulated cells. On the other hand, in Treg cells, TSPAN32 underwent minor changes upon activation. The in vitro data were finally translated into the context of multiple sclerosis (MS). Encephalitogenic T cells from Myelin Oligodendrocyte Glycoprotein (MOG)-Induced Experimental Autoimmune Encephalomyelitis (EAE) mice showed significantly lower levels of TSPAN32 and increased levels of CD9, CD53, CD82 and CD151. Similarly, in vitro-activated circulating CD4 T cells from MS patients showed lower levels of TSPAN32 as compared with cells from healthy donors. Overall, these data suggest an immunoregulatory role for TSPAN32 in T helper immune response and may represent a target of future immunoregulatory therapies for T cell-mediated autoimmune diseases.

Tetraspanins as Organizers of Antigen-Presenting Cell Function

Professional antigen-presenting cells (APCs) include dendritic cells, monocytes, and B cells. APCs internalize and process antigens, producing immunogenic peptides that enable antigen presentation to T lymphocytes, which provide the signals that trigger T-cell activation, proliferation, and differentiation, and lead to adaptive immune responses. After detection of microbial antigens through pattern recognition receptors (PRRs), APCs migrate to secondary lymphoid organs where antigen presentation to T lymphocytes takes place. Tetraspanins are membrane proteins that organize specialized membrane platforms, called tetraspanin-enriched microdomains, which integrate membrane receptors, like PRR and major histocompatibility complex class II (MHC-II), adhesion proteins, and signaling molecules. Importantly, through the modulation of the function of their associated membrane partners, tetraspanins regulate different steps of the immune response. Several tetraspanins can positively or negatively regulate the activation threshold of immune receptors. They also play a role during migration of APCs by controlling the surface levels and spatial arrangement of adhesion molecules and their subsequent intracellular signaling. Finally, tetraspanins participate in antigen processing and are important for priming of naïve T cells through the control of T-cell co-stimulation and MHC-II-dependent antigen presentation. In this review, we discuss the role of tetraspanins in APC biology and their involvement in effective immune responses.

How tetraspanins shape endothelial and leukocyte nano-architecture during inflammation

Tetraspanins are ubiquitous membrane proteins that induce local membrane curvature and hence co-ordinate cell-to-cell contacts. This review highlights their role in inflammation, which requires control of the nano-architecture of attachment sites between endothelial cells and leukocytes. The active role of endothelial cells in preparing for transmigration of leukocytes and determining the severity of an inflammation is often underscored. A clear hint to endothelial pre-activation is their ability to protrude clustered adhesion proteins upward prior to leukocyte contact. The elevation of molecular adhesive platforms toward the blood stream is crucially dependent on tetraspanins. In addition, leukocytes require tetraspanins for their activation. The example of the B-cell receptor is referenced in some detail here, since it provides deeper insights into the receptor-coreceptor interplay. To lift the role of tetraspanins from an abstract model of inflammation toward a player of clinical significance, two pathologies are analyzed for the known contributions of tetraspanins. The recent publication of the first crystal structure of a full-length tetraspanin revealed a cholesterol-binding site, which provides a strong link to the pathophysiological condition of atherosclerosis. Dysregulation of the inflammatory cascade in autoimmune diseases by endothelial cells is exemplified by the involvement of tetraspanins in multiple sclerosis.

The Emerging Role of Tetraspanins in the Proteolytic Processing of the Amyloid Precursor Protein

Tetraspanins are a family of ubiquitously expressed and conserved proteins, which are characterized by four transmembrane domains and the formation of a short and a large extracellular loop (LEL). Through interaction with other tetraspanins and transmembrane proteins such as growth factors, receptors and integrins, tetraspanins build a wide ranging and membrane spanning protein network. Such tetraspanin-enriched microdomains (TEMs) contribute to the formation and stability of functional signaling complexes involved in cell activation, adhesion, motility, differentiation, and malignancy. There is increasing evidence showing that the tetraspanins also regulate the proteolysis of the amyloid precursor protein (APP) by physically interacting with the APP secretases. CD9, CD63, CD81, Tspan12, Tspan15 are among the tetraspanins involved in the intracellular transport and in the stabilization of the gamma secretase complex or ADAM10 as the major APP alpha secretase. They also directly regulate, most likely in concert with other tetraspanins, the proteolytic function of these membrane embedded enzymes. Despite the knowledge about the interaction of tetraspanins with the secretases not much is known about their physiological role, their importance in Alzheimer's Disease and their exact mode of action. This review aims to summarize the current knowledge and open questions regarding the biology of tetraspanins and the understanding how these proteins interact with APP processing pathways. Ultimately, it will be of interest if tetraspanins are suitable targets for future therapeutical approaches.

Function and Dynamics of Tetraspanins during Antigen Recognition and Immunological Synapse Formation

Tetraspanin-enriched microdomains (TEMs) are specialized membrane platforms driven by protein–protein interactions that integrate membrane receptors and adhesion molecules. Tetraspanins participate in antigen recognition and presentation by antigen-­presenting cells (APCs) through the organization of pattern-recognition receptors (PRRs) and their downstream-induced signaling, as well as the regulation of MHC-II–peptide trafficking. T lymphocyte activation is triggered upon specific recognition of antigens present on the APC surface during immunological synapse (IS) formation. This dynamic process is characterized by a defined spatial organization involving the compartmentalization of receptors and adhesion molecules in specialized membrane domains that are connected to the underlying cytoskeleton and signaling molecules. Tetraspanins contribute to the spatial organization and maturation of the IS by controlling receptor clustering and local accumulation of adhesion receptors and integrins, their downstream signaling, and linkage to the actin cytoskeleton. This review offers a perspective on the important role of TEMs in the regulation of antigen recognition and presentation and in the dynamics of IS architectural organization.

Tetraspanins in cell migration

Tetraspanins are a superfamily of small transmembrane proteins that are expressed in almost all eukaryotic cells. Through interacting with one another and with other membrane and intracellular proteins, tetraspanins regulate a wide range of proteins such as integrins, cell surface receptors, and signaling molecules, and thereby engage in diverse cellular processes ranging from cell adhesion and migration to proliferation and differentiation. In particular, tetraspanins modulate the function of proteins involved in all determining factors of cell migration including cell-cell adhesion, cell-ECM adhesion, cytoskeletal protrusion/contraction, and proteolytic ECM remodeling. We herein provide a brief overview of collective in vitro and in vivo studies of tetraspanins to illustrate their regulatory functions in the migration and trafficking of cancer cells, vascular endothelial cells, skin cells (keratinocytes and fibroblasts), and leukocytes. We also discuss the involvement of tetraspanins in various pathologic and remedial processes that rely on cell migration and their potential value as targets for therapeutic intervention.

IL-10 producing B cells partially restore E2-mediated protection against EAE in PD-L1 deficient mice

Women with multiple sclerosis (MS) often experience clinical improvement during pregnancy, indicating that sex hormones might have therapeutic effects in MS. Our previous studies have demonstrated that B cells and PD-L1 are crucial for E2 (17β-estradiol)-mediated protection against experimental autoimmune encephalomyelitis (EAE). We here demonstrate that the transfer of IL-10(+) B cells into E2-treated PD-L1(-/-) mice after EAE induction could partially restore E2-mediated protection and decrease the frequency of pro-inflammatory cells in the CNS compared to E2/saline treated PD-L1(-/-) mice. Hence, co-administration of IL-10(+) B cells and E2 might have a powerful therapeutic potential for treatment of EAE.

Roles for HB-EGF and CD9 in multiple sclerosis

Early events in multiple sclerosis (MS) lesion formation are loss of blood-brain barrier (BBB) integrity, immune cell trafficking into the central nervous system, and demyelination. To date, the molecular mechanisms underlying these pathogenic events are poorly understood. Heparin-binding epidermal growth factor (HB-EGF) is a trophic factor that is induced by inflammatory stimuli and has previously been shown to interact with tetraspanins (TSPs), a family of transmembrane proteins that are involved in cellular migration and adhesion. Given the known roles of TSPs and HB-EGF, we hypothesized that HB-EGF and TSPs may play a role in the processes that underlie MS lesion formation. We examined the expression of HB-EGF and the TSPs CD9 and CD81 in MS brain and found that HB-EGF was highly induced in reactive astrocytes in active lesions. TSPs were constitutively expressed throughout normal appearing white matter and control white matter. In contrast, CD9 was reduced in demyelinated lesions and increased on blood vessels in lesion areas. In vitro studies revealed that expression of HB-EGF and TSPs is regulated during inflammation. Importantly, blocking either HB-EGF or CD9 significantly reduced the migration of monocytes across brain endothelial cell monolayers. Moreover, blocking CD9 strongly enhanced the barrier function of the BBB in vitro. Together, we demonstrate that these molecules are likely implicated in processes that are highly relevant for MS lesion formation, and therefore, HB-EGF and TSPs are promising therapeutic targets.

Characterization of tetraspanins CD9, CD53, CD63, and CD81 in monocytes and macrophages in HIV-1 infection

Tetraspanins are a family of membrane-organizing proteins that mediate diverse functions. Little is known of their expression or function in myeloid cells. Here, expression of CD9, CD53, CD63, and CD81, tetraspanins that have been implicated in HIV-1 pathogenesis, were characterized in normal monocyte subsets, in MDM, and in HIV-1-infected donors. We show that tetraspanins are expressed differentially by monocyte subsets, with higher CD9 and CD63 and lower CD53 and CD81 levels on CD14++CD16- monocytes compared with CD14++CD16+ and CD14+CD16++ subsets. Maturation of monocytes resulted in increased CD9 expression and apparent relocation of CD63 and CD53 from surface to intracellular membranes. Expression was modulated by cytokines, and CD9 was a marker of anti-inflammatory and CD53 a marker of proinflammatory MDM. Tetraspanin expression on monocyte subsets from HIV-1-infected donors receiving antiretroviral therapy was unchanged compared with that in uninfected donors. However, CD53 expression was inversely correlated with viral load in HIV-1-infected donors not on therapy. This study is the first to comprehensively characterize tetraspanin expression on monocyte subsets and macrophages in health and during HIV-1 infection. It demonstrates regulation of tetraspanin expression by cytokines, and CD53 expression as a novel correlate of a proinflammatory phenotype. This paper characterizes tetraspanins in myeloid cells and shows that tetraspanins are expressed differentially in monocyte subsets and are modified in inflammatory conditions.

CD81 regulates cell migration through its association with Rac GTPase

Data presented here provide evidence for a new direct interaction of the GTPase Rac with the C-terminal cytoplasmic domain of tetraspanin CD81. Tetraspanin-enriched, microdomain-dependent compartmentalization is a novel regulatory mechanism of Rac activity turnover, which provides a novel mechanism for regulation of cell motility by tetraspanins.

CD81 is a member of the tetraspanin family that has been described to have a key role in cell migration of tumor and immune cells. To unravel the mechanisms of CD81-regulated cell migration, we performed proteomic analyses that revealed an interaction of the tetraspanin C-terminal domain with the small GTPase Rac. Direct interaction was confirmed biochemically. Moreover, microscopy cross-correlation analysis demonstrated the in situ integration of both molecules into the same molecular complex. Pull-down experiments revealed that CD81-Rac interaction was direct and independent of Rac activation status. Knockdown of CD81 resulted in enhanced protrusion rate, altered focal adhesion formation, and decreased cell migration, correlating with increased active Rac. Reexpression of wild-type CD81, but not its truncated form lacking the C-terminal cytoplasmic domain, rescued these effects. The phenotype of CD81 knockdown cells was mimicked by treatment with a soluble peptide with the C-terminal sequence of the tetraspanin. Our data show that the interaction of Rac with the C-terminal cytoplasmic domain of CD81 is a novel regulatory mechanism of the GTPase activity turnover. Furthermore, they provide a novel mechanism for tetraspanin-dependent regulation of cell motility and open new avenues for tetraspanin-targeted reagents by the use of cell-permeable peptides.

Lymphocyte phenotypes in wild-caught rats suggest potential mechanisms underlying increased immune sensitivity in post-industrial environments

The immune systems of wild rats and of laboratory rats can been utilized as models of the human immune system in pre-industrial and post-industrial societies, respectively. In this study, lymphocyte phenotypes in wild rats were broadly characterized, and the results were compared to those obtained by us and by others using cells derived from various strains of laboratory rats. Although not expected, the production of regulatory T cells was not apparently different in wild rats compared to laboratory rats. On the other hand, differences in expression of markers involved in complement regulation, adhesion, signaling and maturation suggest increased complement regulation and decreased sensitivity in wild-caught rats compared to laboratory rats, and point toward complex differences between the maturation of T cells. The results potentially lend insight into the pathogenesis of post-industrial epidemics of allergy and autoimmune disease.

Role of Ninjurin-1 in the migration of myeloid cells to central nervous system inflammatory lesions

OBJECTIVE

Blood-derived myeloid antigen-presenting cells (APCs) account for a significant proportion of the leukocytes found within lesions of multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE). These APCs along with activated microglia are thought to be pivotal in the initiation of the central nervous system (CNS)-targeted immune response in MS and EAE. However, the exact molecules that direct the migration of myeloid cells from the periphery across the blood-brain barrier (BBB) remain largely unknown.

METHODS

We identified Ninjurin-1 in a proteomic screen of human BBB endothelial cells (ECs). We assessed the expression of Ninjurin-1 by BBB-ECs and immune cells, and we determined the role of Ninjurin-1 in immune cell migration to the CNS in vivo in EAE mice.

RESULTS

Ninjurin-1 was found to be weakly expressed in the healthy human and mouse CNS but upregulated on BBB-ECs and on infiltrating APCs during the course of EAE and in active MS lesions. In human peripheral blood, Ninjurin-1 was predominantly expressed by monocytes, whereas it was barely detectable on T and B lymphocytes. Moreover, Ninjurin-1 neutralization specifically abrogated the adhesion and migration of human monocytes across BBB-ECs, without affecting lymphocyte recruitment. Finally, Ninjurin-1 blockade reduced clinical disease activity and histopathological indices of EAE and decreased infiltration of macrophages, dendritic cells, and APCs into the CNS.

INTERPRETATION

Our study uncovers an important cell-specific role for Ninjurin-1 in the transmigration of inflammatory APCs across the BBB and further emphasizes the importance of myeloid cell recruitment during the development of neuroinflammatory lesions.

Functional interplay between tetraspanins and proteases

Several recent publications have described examples of physical and functional interations between tetraspanins and specific membrane proteases belonging to the TM-MMP and α-(ADAMs) and γ-secretases families. Collectively, these examples constitute an emerging body of evidence supporting the notion that tetraspanin-enriched microdomains (TEMs) represent functional platforms for the regulation of key cellular processes including the release of surface protein ectodomains ("shedding"), regulated intramembrane proteolysis ("RIPing") and matrix degradation and assembly. These cellular processes in turn play a crucial role in an array of physiological and pathological phenomena. Thus, TEMs may represent new therapeutical targets that may simultaneously affect the proteolytic activity of different enzymes and their substrates. Agonistic or antagonistic antibodies and blocking soluble peptides corresponding to tetraspanin functional regions may offer new opportunities in the treatment of pathologies such as chronic inflammation, cancer, or Alzheimer's disease. In this review article, we will discuss all these aspects of functional regulation of protease activities by tetraspanins.

Review: leucocyte-endothelial cell crosstalk at the blood-brain barrier: a prerequisite for successful immune cell entry to the brain

Leucocyte migration into the central nervous system is a key stage in the development of multiple sclerosis. While much has been learnt regarding the sequential steps of leucocyte capture, adhesion and migration across the vasculature, the molecular basis of leucocyte extravasation is only just being unravelled. It is now recognized that bidirectional crosstalk between the immune cell and endothelium is an essential element in mediating diapedesis during both normal immune surveillance and under inflammatory conditions. The induction of various signalling networks, through engagement of cell surface molecules such as integrins on the leucocyte and immunoglobulin superfamily cell adhesion molecules on the endothelial cell, play a major role in determining the pattern and route of leucocyte emigration. In this review we discuss the extent of our knowledge regarding leucocyte migration across the blood-brain barrier and in particular the endothelial cell signalling pathways contributing to this process.

ICAM-1 clustering on endothelial cells recruits VCAM-1

In the initial stages of transendothelial migration, leukocytes use the endothelial integrin ligands ICAM-1 and VCAM-1 for strong adhesion. Upon adhesion of the leukocyte to endothelial ICAM-1, ICAM-1 is clustered and recruited to the adhered leukocyte, promoting strong adhesion. In this study, we provide evidence for the colocalization of VCAM-1 at sites of ICAM-1 clustering. Anti-ICAM-1 antibody-coated beads were used to selectively cluster and recruit ICAM-1 on primary human endothelial cells. In time, co-localization of ICAM-1 and VCAM-1 around the adherent beads was observed. Biochemical pull-down assays showed that ICAM-1 clustering induced its association to VCAM-1, suggesting a physical link between these two adhesion molecules. The association was partly dependent on lipid rafts as well as on F-actin and promoted adhesion. These data show that VCAM-1 can be recruited, in an integrin-independent fashion, to clustered ICAM-1 which may serve to promote ICAM-1-mediated leukocyte adhesion.

Regulation of NK cell trafficking by CD81

NK cells, a heterogeneous sub-population of lymphocytes, are critically involved in the regulation of both innate and adaptive immune responses in humans. Besides their participation in the control of tumors and viral infections, they also regulate inflammatory processes, mediating both beneficial and detrimental effects. To effectively fulfil their role in immune surveillance, proper trafficking of NK cells is essential. However, the mechanisms and factors governing NK cell recruitment are only poorly dissected. Here, we describe the functional role of tetraspanins, a family of evolutionary conserved cell-surface proteins, in modulating migration and transmigration of human NK cells. We demonstrate expression of various tetraspanins on NK cells. Furthermore, we show that stimulation of the NK cell-expressed tetraspanin CD81 induces phosphorylation of ezrin/radixin/moesin proteins and leads to NK cell polarization thereby facilitating NK cell migration toward various chemokines/cytokines. Finally, we provide evidence for a role of CD81 in promoting adhesion of NK cells to components of the extracellular matrix, a prerequisite for extravasation of lymphocytes in inflamed tissues. Thus, our data suggest that the tetraspanin CD81 is importantly involved in the regulation of NK cell recruitment.

Small interfering RNA targeting CD81 ameliorated arthritis in rats

CD81 belongs to a family of cell-surface protein (tetraspanin) known as one of the up-regulated elements in rheumatoid arthritis synoviocytes. In this study, the therapeutic effect of small interfering RNA targeting CD81 (siCD81) was examined by in vivo electroporation method. Treatment with siCD81 significantly ameliorated paw swelling of collagen-induced arthritic (CIA) rats. In histological examination, hypertrophy of synovium, bone erosion, and degeneration of articular cartilage were milder in rats treated with siCD81 than in the control group and the non-specific siRNA group. Expression of synoviolin, a rheumatoid regulator, was suppressed by siCD81. Thus, therapeutic intervention by targeting CD81 may be used in the treatment of rheumatoid arthritis.

Functions of lipid raft membrane microdomains at the blood-brain barrier

The blood-brain barrier (BBB) is a highly specialized structural and functional component of the central nervous system that separates the circulating blood from the brain and spinal cord parenchyma. Brain endothelial cells (BECs) that primarily constitute the BBB are tightly interconnected by multiprotein complexes, the adherens junctions and the tight junctions, thereby creating a highly restrictive cellular barrier. Lipid-enriched membrane microdomain compartmentalization is an inherent property of BECs and allows for the apicobasal polarity of brain endothelium, temporal and spatial coordination of cell signaling events, and actin remodeling. In this manuscript, we review the role of membrane microdomains, in particular lipid rafts, in the BBB under physiological conditions and during leukocyte transmigration/diapedesis. Furthermore, we propose a classification of endothelial membrane microdomains based on their function, or at least on the function ascribed to the molecules included in such heterogeneous rafts: (1) rafts associated with interendothelial junctions and adhesion of BECs to basal lamina (scaffolding rafts); (2) rafts involved in immune cell adhesion and migration across brain endothelium (adhesion rafts); (3) rafts associated with transendothelial transport of nutrients and ions (transporter rafts).