Immunoregulatory functions of KLRG1 cadherin interactions are dependent on forward and reverse signaling

Memory inflation: Beyond the acute phase of viral infection

Memory inflation is confirmed as the most commonly dysregulation of host immunity with antigen-independent manner in mammals after viral infection. By generating large numbers of effector/memory and terminal differentiated effector memory CD8+ T cells with diminished naïve subsets, memory inflation is believed to play critical roles in connecting the viral infection and the onset of multiple diseases. Here, we reviewed the current understanding of memory inflated CD8+ T cells in their distinct phenotypic features that different from exhausted subsets; the intrinsic and extrinsic roles in regulating the formation of memory inflation; and the key proteins in maintaining the expansion and proliferation of inflationary populations. More importantly, based on the evidences from both clinic and animal models, we summarized the potential mechanisms of memory inflation to trigger autoimmune neuropathies, such as Guillain-Barré syndrome and multiple sclerosis; the correlations of memory inflation between tumorigenesis and resistance of tumour immunotherapies; as well as the effects of memory inflation to facilitate vascular disease progression. To sum up, better understanding of memory inflation could provide us an opportunity to beyond the acute phase of viral infection, and shed a light on the long-term influences of CD8+ T cell heterogeneity in dampen host immune homeostasis.

The role of KLRG1: a novel biomarker and new therapeutic target

Killer cell lectin-like receptor G1 (KLRG1) is an immune checkpoint receptor expressed predominantly in NK and T-cell subsets that downregulates the activation and proliferation of immune cells and participates in cell-mediated immune responses. Accumulating evidence has demonstrated the importance of KLRG1 as a noteworthy disease marker and therapeutic target that can influence disease onset, progression, and prognosis. Blocking KLRG1 has been shown to effectively mitigate the effects of downregulation in various mouse tumor models, including solid tumors and hematologic malignancies. However, KLRG1 inhibitors have not yet been approved for human use, and the understanding of KLRG1 expression and its mechanism of action in various diseases remains incomplete. In this review, we explore alterations in the distribution, structure, and signaling pathways of KLRG1 in immune cells and summarize its expression patterns and roles in the development and progression of autoimmune diseases, infectious diseases, and cancers. Additionally, we discuss the potential applications of KLRG1 as a tool for tumor immunotherapy.

Targeting MCL1-driven anti-apoptotic pathways overcomes blast progression after hypomethylating agent failure in chronic myelomonocytic leukemia

RAS pathway mutations, which are present in 30% of patients with chronic myelomonocytic leukemia (CMML) at diagnosis, confer a high risk of resistance to and progression after hypomethylating agent (HMA) therapy, the current standard of care for the disease. Here, using single-cell, multi-omics technologies, we seek to dissect the biological mechanisms underlying the initiation and progression of RAS pathway-mutated CMML. We identify that RAS pathway mutations induce transcriptional reprogramming of hematopoietic stem and progenitor cells (HSPCs) and downstream monocytic populations in response to cell-intrinsic and -extrinsic inflammatory signaling that also impair the functions of immune cells. HSPCs expand at disease progression after therapy with HMA or the BCL2 inhibitor venetoclax and rely on the NF-κB pathway effector MCL1 to maintain survival. Our study has implications for the development of therapies to improve the survival of patients with RAS pathway-mutated CMML.

The Essential Role of microRNAs in Inflammatory and Autoimmune Skin Diseases-A Review

The etiopathogenesis of autoimmune skin diseases is complex and still not fully understood. The role of epigenetic factors is emphasized in the development of such diseases. MicroRNAs (miRNAs), a group of non-coding RNAs (ncRNAs-non-coding RNAs), are one of the important post-transcriptional epigenetic factors. miRNAs have a significant role in the regulation of the immune response by participating in the process of the differentiation and activation of B and T lymphocytes, macrophages, and dendritic cells. Recent advances in research on epigenetic factors have provided new insights into the pathogenesis and potential diagnostic and therapeutic targets of many pathologies. Numerous studies revealed a change in the expression of some microRNAs in inflammatory skin disorders, and the regulation of miRNA expression is a promising therapeutic goal. This review presents the state of the art regarding changes in the expression and role of miRNAs in inflammatory and autoimmune skin diseases, including psoriasis, atopic dermatitis, vitiligo, lichen planus, hidradenitis suppurativa, and autoimmune blistering diseases.

E-Cadherin Expression Distinguishes Mouse from Human Hematopoiesis in the Basophil and Erythroid Lineages

E-cadherin is a key regulator of epithelial cell-cell adhesion, the loss of which accelerates tumor growth and invasion. E-cadherin is also expressed in hematopoietic cells as well as epithelia. The function of hematopoietic E-cadherin is, however, mostly elusive. In this study, we explored the validity of mouse models to functionally investigate the role of hematopoietic E-cadherin in human hematopoiesis. We generated a hematopoietic-specific E-cadherin knockout mouse model. In mice, hematopoietic E-cadherin is predominantly expressed within the basophil lineage, the expression of which is dispensable for the generation of basophils. However, neither E-cadherin mRNA nor protein were detected in human basophils. In contrast, human hematopoietic E-cadherin marks the erythroid lineage. E-cadherin expression in hematopoiesis thereby revealed striking evolutionary differences between the basophil and erythroid cell lineage in humans and mice. This is remarkable as E-cadherin expression in epithelia is highly conserved among vertebrates including humans and mice. Our study therefore revealed that the mouse does not represent a suitable model to study the function of E-cadherin in human hematopoiesis and an alternative means to study the role of E-cadherin in human erythropoiesis needs to be developed.

Role of PARP Inhibitors in Cancer Immunotherapy: Potential Friends to Immune Activating Molecules and Foes to Immune Checkpoints

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) induce cytotoxic effects as single agents in tumors characterized by defective repair of DNA double-strand breaks deriving from BRCA1/2 mutations or other abnormalities in genes associated with homologous recombination. Preclinical studies have shown that PARPi-induced DNA damage may affect the tumor immune microenvironment and immune-mediated anti-tumor response through several mechanisms. In particular, increased DNA damage has been shown to induce the activation of type I interferon pathway and up-regulation of PD-L1 expression in cancer cells, which can both enhance sensitivity to Immune Checkpoint Inhibitors (ICIs). Despite the recent approval of ICIs for a number of advanced cancer types based on their ability to reinvigorate T-cell-mediated antitumor immune responses, a consistent percentage of treated patients fail to respond, strongly encouraging the identification of combination therapies to overcome resistance. In the present review, we analyzed both established and unexplored mechanisms that may be elicited by PARPi, supporting immune reactivation and their potential synergism with currently used ICIs. This analysis may indicate novel and possibly patient-specific immune features that might represent new pharmacological targets of PARPi, potentially leading to the identification of predictive biomarkers of response to their combination with ICIs.

Natural killer cells and immune-checkpoint inhibitor therapy: Current knowledge and new challenges

The discovery of immune checkpoints (ICs) and the development of specific blockers to relieve immune effector cells from this inhibiting mechanism has changed the view of anti-cancer therapy. In addition to cytotoxic T lymphocyte antigen 4 (CTLA4) and programmed death 1 (PD1), classical ICs of T lymphocytes and recently described also on a fraction of natural killer (NK) cells, several NK cell receptors, including killer immunoglobulin-like inhibitory receptors (KIRs) and NGK2A, have been recognized as checkpoint members typical of the NK cell population. This offers the opportunity of a dual-checkpoint inhibition approach, targeting classical and non-classical ICs and leading to a synergistic therapeutic effect. In this review, we will overview and discuss this new perspective, focusing on the most relevant candidates for this role among the variety of potential NK ICs. Beside listing and defining classical ICs expressed also by NK cells, or non-classical ICs either on T or on NK cells, we will address their role in NK cell survival, chronic stimulation or functional exhaustion, and the potential relevance of this phenomenon on anti-tumor immune response. Furthermore, NK ICs will be proposed as possible new targets for the development of efficient combined immunotherapy, not forgetting the relevant concerns that may be raised on NK IC blockade. Finally, the impact of epigenetic drugs in such a complex therapeutic picture will be briefly addressed.

An atypical KLRG1 in Nile tilapia involves in adaptive immunity as a potential marker for activated T lymphocytes

Killer cell lectin-like receptor G subfamily 1 (KLRG1) is a receptor generally expressed on effector CD8⁺ T cells or NK cells at terminal differentiation stage, and it will be highly induced for lymphocyte cytotoxicity upon pathogen infection or lymphocyte activation. However, little is known about the character or function of KLRG1 in lower vertebrates. In present study, we reappraised a molecule that previously defined as KLRG1 in the genomic sequence of Nile tilapia Oreochromis niloticus, and identified it as an atypical KLRG1-like molecule (defined as On-KLRG1-L), and illustrated its potential function serving as a marker representing effector T lymphocytes of fish species. On-KLRG1-L consists of two C-type lectin-like domains (CTLDs) without transmembrane region, and the tertiary structure of the CTLD is highly alike to that in mouse KLRG1. As a CTLD-containing protein, the recombinant On-KLRG1-L could bind PGN and several microbes in vitro. On-KLRG1-L was widely expressed in immune-associated tissues, with the highest expression level in the gill. Once Nile tilapia is infected by Aeromonas hydrophila, mRNA level of On-KLRG1-L in spleen lymphocytes were significantly up-regulated on 5 days after infection. Meanwhile, On-KLRG1-L protein was also induced on 5 or 8 days after A. hydrophila infection. Furthermore, we found both mRNA and protein levels of On-KLRG1-L were dramatically enhanced within several hours after spleen lymphocytes were activated by T cell-specific mitogen PHA in vitro. More importantly, the ratio of On-KLRG1-L⁺ T cells was also augmented after PHA stimulation. The observations suggested that the KLRG1-like molecule from Nile tilapia participated in lymphocyte activation and anti-bacterial adaptive immune response, and could serve as an activation marker of T lymphocytes. Our study thus provided new evidences to understand lymphocyte-mediated adaptive immunity of teleost.

MicroRNAs in pemphigus and pemphigoid diseases

Autoimmune blistering diseases are a heterogenous group of dermatological disorders characterized by blisters and erosions of the skin and/or mucous membranes induced by autoantibodies against structural proteins of the desmosome or the dermal-epidermal adhesion complex including the hemidesmosome. They consist of the two major disease groups, pemphigus and pemphigoid diseases (PPDs). The diagnosis is based on clinical findings, histopathology, direct immunofluorescence, and detection of circulating autoantibodies. The pathogenesis is not fully elucidated, prognostic factors are lacking, and to date, there is no cure for PPDs. MicroRNAs (miRNAs) represent small, non-coding RNAs that play a pivotal role in the posttranscriptional regulation of gene expression. Their dysfunction was highlighted to play a significant role in the pathogenesis of various diseases. Even though a link between miRNAs and autoimmune blistering diseases had been suggested, the research of their involvement in the pathogenesis of PPDs is still in its infancy. miRNAs hold promise for uncovering new layers in the pathogenesis of PPDs, in order to improve diagnosis and also to develop potential therapeutic options. In the current article, we provide an overview regarding current knowledge of miRNAs in terms of complex pathogenesis of PPDs, and, also, their potential role as biomarkers, predictive factors and therapeutic targets.

Unbiased Profiling Reveals Compartmentalization of Unconventional T-Cells Within the Intestinal Mucosa Irrespective of HIV Infection

The intestinal mucosa is enriched for unconventional T-cells, including mucosal associated invariant T-cells (MAIT), invariant natural killer T-cells (iNKT) and γδ T-cells. These cells are activated by bacterial metabolites, lipid antigens and cytokines, and are important for intestinal barrier integrity. The loss of gut homeostasis observed in HIV infection is central to disease pathogenesis, and studies have highlighted impairment of particular unconventional T-cell subsets within a specific gut compartment. However, although the small and large intestine are distinct niches, the overall impact of HIV on unconventional T-cells across the gut mucosal has not been well-studied. We hypothesized that compartment specific differences in the unconventional T-cell repertoire would exist between the small and large intestine, due to increasing bacterial loads and microbial diversity; and that the impact of HIV infection might differ depending on the compartment examined. We used mass cytometry, flow cytometry and unbiased T-cell receptor profiling to quantify unconventional T-cells in blood and tissue from the small (duodenum) and large (colon) intestine in HIV infected and uninfected participants undergoing examination for a range of intestinal conditions. Overall, we find distinct compartmentalisation of T-cells between blood, duodenum and colon, with iNKT cells significantly enriched in the duodenum and δ-1 expressing γδ T-cells in the colon. In addition, we observe greater clonal expansion of conventional TCRs in the duodenum, suggestive of stronger adaptive immunity in this compartment. Conversely, we find evidence of an expanded unconventional TCR repertoire in the colon, which contained far more overlapping “donor unrestricted” sequences than the duodenum. Twelve of these TCRs were highly “MAIT-like” and 3 were unique to the colon, suggesting an enrichment of donor unrestricted T-cells (DURTs) in this compartment. Unexpectedly, however, no significant impact of HIV infection on any of the unconventional T-cell subsets measured was observed in either mucosal site in terms of frequency or TCR repertoire. Further studies are required to investigate the importance of these unconventional T-cell subsets to intestinal homeostasis within the different gut compartments and determine if they are functionally impaired during HIV infection.

Drugs Modulating CD4+ T Cells Blood-Brain Barrier Interaction in Alzheimer's Disease

The effect of Alzheimer’s disease (AD) medications on CD4+ T cells homing has not been thoroughly investigated. CD4+ T cells could both exacerbate and reduce AD symptoms based on their infiltrating subpopulations. Proinflammatory subpopulations such as Th1 and Th17 constitute a major source of proinflammatory cytokines that reduce endothelial integrity and stimulate astrocytes, resulting in the production of amyloid β. Anti-inflammatory subpopulations such as Th2 and Tregs reduce inflammation and regulate the function of Th1 and Th17. Recently, pathogenic Th17 has been shown to have a superior infiltrating capacity compared to other major CD4+ T cell subpopulations. Alzheimer’s drugs such as donepezil (Aricept), rivastigmine (Exelon), galantamine (Razadyne), and memantine (Namenda) are known to play an important part in regulating the mechanisms of the neurotransmitters. However, little is known about the effect of these drugs on CD4+ T cell subpopulations’ infiltration of the brain during AD. In this review, we focus on understanding the influence of AD drugs on CD4+ T cell subpopulation interactions with the BBB in AD. While current AD therapies improve endothelial integrity and reduce astrocytes activations, they vary according to their influence on various CD4+ T cell subpopulations. Donepezil reduces the numbers of Th1 but not Th2, Rivastigmine inhibits Th1 and Th17 but not Th2, and memantine reduces Th1 but not Treg. However, none of the current AD drugs is specifically designed to target the dysregulated balance in the Th17/Treg axis. Future drug design approaches should specifically consider inhibiting CD4+ Th17 to improve AD prognosis.

An Overview of the Derivation and Function of Multinucleated Giant Cells and Their Role in Pathologic Processes

Monocyte lineage cells play important roles in health and disease. Their differentiation into macrophages is crucial for a broad array of immunologic processes that regulate inflammation, neoplasia, and infection. In certain pathologic conditions, such as foreign body reactions and peripheral inflammatory lesions, monocytes fuse to form large, multinucleated giant cells (MGCs). Currently, our knowledge of the fusion mechanisms of monocytes and the regulation of MGC formation and function in discrete pathologies is limited. Herein, we consider the types and function of MGCs in disease and assess the mechanisms by which monocyte fusion contributes to the formation of MGCs. An improved understanding of the cellular origins and metabolic functions of MGCs will facilitate their identification and ultimately the treatment of diseases and disorders that involve MGCs.

CD103 (αE Integrin) Undergoes Endosomal Trafficking in Human Dendritic Cells, but Does Not Mediate Epithelial Adhesion

Dendritic cell (DC) expression of CD103, the α subunit of αEβ7 integrin, is thought to enable DC interactions with E-cadherin-expressing gastrointestinal epithelia for improved mucosal immunosurveillance. In the stomach, efficient DC surveillance of the epithelial barrier is crucial for the induction of immune responses to H. pylori, the causative agent of peptic ulcers and gastric cancer. However, gastric DCs express only low levels of surface CD103, as we previously showed. We here tested the hypothesis that intracellular pools of CD103 in human gastric DCs can be redistributed to the cell surface for engagement of epithelial cell-expressed E-cadherin to promote DC-epithelial cell adhesion. In support of our hypothesis, immunofluorescence analysis of tissue sections showed that CD103+ gastric DCs were preferentially localized within the gastric epithelial layer. Flow cytometry and imaging cytometry revealed that human gastric DCs expressed intracellular CD103, corroborating our previous findings in monocyte-derived DCs (MoDCs). Using confocal microscopy, we show that CD103 was present in endosomal compartments, where CD103 partially co-localized with clathrin, early endosome antigen-1 and Rab11, suggesting that CD103 undergoes endosomal trafficking similar to β1 integrins. Dynamic expression of CD103 on human MoDCs was confirmed by internalization assay. To analyze whether DC-expressed CD103 promotes adhesion to E-cadherin, we performed adhesion and spreading assays on E-cadherin-coated glass slides. In MoDCs generated in the presence of retinoic acid, which express increased CD103, intracellular CD103 significantly redistributed toward the E-cadherin-coated glass surface. However, DCs spreading and adhesion did not differ between E-cadherin-coated slides and slides coated with serum alone. In adhesion assays using E-cadherin-positive HT-29 cells, DC binding was significantly improved by addition of Mn2+ and decreased in the presence of EGTA, consistent with the dependence of integrin-based interactions on divalent cations. However, retinoic acid failed to increase DC adhesion, and a CD103 neutralizing antibody was unable to inhibit DC binding to the E-cadherin positive cells. In contrast, a blocking antibody to DC-expressed E-cadherin significantly reduced DC binding to the epithelium. Overall, these data indicate that CD103 engages in DC-epithelial cell interactions upon contact with epithelial E-cadherin, but is not a major driver of DC adhesion to gastrointestinal epithelia.

A Pan-cancer Landscape of Interactions between Solid Tumors and Infiltrating Immune Cell Populations

Purpose: Throughout their development, tumors are challenged by the immune system, and they acquire features to evade its surveillance. A systematic view of these traits, which shed light on how tumors respond to immunotherapies, is still lacking.Experimental Design: Here, we computed the relative abundance of an array of immune cell populations to measure the immune infiltration pattern of 9,174 tumors of 29 solid cancers. We then clustered tumors with similar infiltration pattern to define immunophenotypes. Finally, we identified genomic and transcriptomic traits associated to these immunophenotypes across cancer types.Results: In highly cytotoxic immunophenotypes, we found tumors with low clonal heterogeneity enriched for alterations of genes involved in epigenetic regulation, ubiquitin-mediated proteolysis, antigen presentation, and cell-cell communication, which may drive resistance in combination with the ectopic expression of negative immune checkpoints. Tumors with immunophenotypes of intermediate cytotoxicity are characterized by an upregulation of processes involved in neighboring tissue invasion and remodeling that may foster the recruitment of immunosuppressive cells. Tumors with poorly cytotoxic immunophenotype tend to be of more advanced stages and bear a greater burden of copy number alterations and frequent alterations of cell cycle, hedgehog, β-catenin, and TGFβ pathways, which may cause immune depletion.Conclusions: We provide a comprehensive landscape of the characteristics of solid tumors that may influence (or be influenced by) the characteristics of their immune infiltrate. These results may help interpret the response of solid tumors to immunotherapies and guide the development of novel drug combination strategies. Clin Cancer Res; 24(15); 3717-28. ©2018 AACR.

Suppression of Immunotherapy on Group 2 Innate Lymphoid Cells in Allergic Rhinitis

Background:

Group 2 innate lymphoid cells (ILC2s) are regarded as a novel population of lineage-negative cells that induce innate Type 2 responses by producing the critical Th2-type cytokines interleukin (IL)-5 and IL-13. ILC2s as key players in the development of allergic rhinitis (AR) have been proved, however, the effect of subcutaneous immunotherapy (SCIT) with dermatophagoides pteronyssinus extract (Der p-SCIT) on ILC2s in AR patients is not clear. This study aimed to investigate the response of ILC2s of peripheral blood in house dust mites (HDM)-sensitized Chinese patients with AR who received SCIT with Der P extract.

Methods:

Seven healthy controls without symptoms of AR who had negative reactions to any of the allergens from skin-prick testing, nine patients diagnosed with persistent AR according to the Allergic Rhinitis and its Impact on Asthma (ARIA) guidelines, and 24 AR patients who received Der p-SCIT for 1.0–3.5 years were recruited for the study. ILC2s in the peripheral blood were evaluated using flow cytometry. The severity of their symptoms of all participants was rated based on the Total 5 symptom score.

Results:

Among 40 participants, 9 AR patients were assigned to the untreated group, 24 AR patients receiving Der p-SCIT were assigned to the immunotherapy group, and 7 healthy controls without symptoms of AR were assigned to healthy control group. The mean Total 5 symptom score of immunotherapy group was significantly lower than that of untreated group (4.3 ± 1.4 vs. 10.1 ± 2.5, P < 0.001). Similarly, the levels of ILC2s in the peripheral blood of immunotherapy group were significantly reduced compared with that in untreated group (P < 0.001), but were not significantly different from healthy controls (P = 0.775). Further subgroup analysis based on the duration of SCIT therapy (1.0–2.0 years [SCIT_1-2], 2.0–3.0 years [SCIT_2-3], and 3.0–3.5 years [SCIT_3-3.5]) showed that the percentage of ILC2s was not significantly different between SCIT_1-2, SCIT_2-3, and SCIT_3-3.5 groups (SCIT_1-2 vs. SCIT_2-3: P = 0.268; SCIT_1-2 vs. SCIT_3-3.5: P = 0.635; and SCIT_2-3 vs. SCIT_3-3.5: P = 0.787).

Conclusions:

The present study highlighted the suppression of Der p-SCIT on ILC2s in HDM-AR patients. ILC2s identified in peripheral blood can be used as an effective biomarker for Der p-SCIT.

Heterocellular cadherin connections: coordinating adhesive cues in homeostasis and cancer

This short insight covers some of the recent topics relevant to the field of cadherin-catenin adhesion in mediating connections between different cell types, so-called heterotypic or heterocellular connections, in both homeostasis and cancer. These scientific discoveries are increasing our understanding of how multiple cells residing in complex tissues can be instructed by cadherin adhesion receptors to regulate tissue architecture and function and how these cadherin-mediated heterocellular connections spur tumor growth and the acquisition of malignant characteristics in tumor cells. Overall, the findings that have emerged over the past few years are elucidating the complexity of the functional roles of the cadherin-catenin complexes. Future exciting research lies ahead in order to understand the physical basis of these heterotypic interactions and their influence on the behavior of heterogeneous cellular populations as well as their roles in mediating phenotypic and genetic changes as cells evolve through complex environments during morphogenesis and cancer.

E-cadherin expression in macrophages dampens their inflammatory responsiveness in vitro, but does not modulate M2-regulated pathologies in vivo

IL-4/IL-13-induced alternatively activated macrophages (M(IL-4/IL-13), AAMs or M2) are known to express E-cadherin, enabling them to engage in heterotypic cellular interactions and IL-4-driven macrophage fusion in vitro. Here we show that E-cadherin overexpression in Raw 264.7 macrophages inhibits their inflammatory response to LPS stimulation, as demonstrated by a reduced secretion of inflammatory mediators like interleukin (IL)-6, tumor necrosis factor (TNF) and nitric oxide (NO). To study the function of E-cadherin in M(IL-4/IL-13) macrophages in vivo, we generated macrophage-specific E-cadherin-deficient C57BL/6 mice. Using this new tool, we analyzed immunological parameters during two typical AAM-associated Th2-driven diseases and assessed Th2-associated granuloma formation. Although E-cadherin is strongly induced in AAMs during Taenia crassiceps helminth infections and allergic airway inflammation, its deletion in macrophages does not affect the course of both Th2 cytokine-driven diseases. Moreover, macrophage E-cadherin expression is largely redundant for granuloma formation around Schistosoma mansoni ova. Overall, we conclude that E-cadherin is a valuable AAM marker which suppresses the inflammatory response when overexpressed. Yet E-cadherin deletion in macrophages does not affect M(LPS+IFNγ) and M(IL-4) polarization in vitro, nor in vivo macrophage function, at least in the conditions tested.

NKG2D is a Key Receptor for Recognition of Bladder Cancer Cells by IL-2-Activated NK Cells and BCG Promotes NK Cell Activation

Intravesical instillation of bacillus Calmette–Guérin (BCG) is used to treat superficial bladder cancer, either papillary tumors (after transurethral resection) or high-grade flat carcinomas (carcinoma in situ), reducing recurrence in about 70% of patients. Initially, BCG was proposed to work through an inflammatory response, mediated by phagocytic uptake of mycobacterial antigens and cytokine release. More recently, other immune effectors such as monocytes, natural killer (NK), and NKT cells have been suggested to play a role in this immune response. Here, we provide a comprehensive study of multiple bladder cancer cell lines as putative targets for immune cells and evaluated their recognition by NK cells in the presence and absence of BCG. We describe that different bladder cancer cells can express multiple activating and inhibitory ligands for NK cells. Recognition of bladder cancer cells depended mainly on NKG2D, with a contribution from NKp46. Surprisingly, exposure to BCG did not affect the immune phenotype of bladder cells nor increased NK cell recognition of purified IL-2-activated cell lines. However, NK cells were activated efficiently when BCG was included in mixed lymphocyte cultures, suggesting that NK activation after mycobacteria treatment requires the collaboration of various immune cells. We also analyzed the percentage of NK cells in peripheral blood of a cohort of bladder cancer patients treated with BCG. The total numbers of NK cells did not vary during treatment, indicating that a more detailed study of NK cell activation in the tumor site will be required to evaluate the response in each patient.

Transferrin' activation: bonding with transferrin receptors tunes KLRG1 function

The inhibitory C-type lectin-like immunoreceptor KLRG1 enables mature NK cells and differentiated T cells to sense cadherin-expressing cells by ligating "classical" cadherins. Upon engagement of the KLRG1 ectodomain, an inhibitory signal emanates from the cytoplasmic immunoreceptor-tyrosine-based inhibition motif (ITIM), dampening functional responses of these lymphocytes. Malignancy-associated loss of cadherins has been proposed to relieve KLRG1-mediated inhibition of cytotoxic lymphocytes and thereby to contribute to tumor surveillance by an alternate mode of "missing self-recognition". In this issue of the European Journal of Immunology, Schweier et al. [Eur. J. Immunol. 2014. 44: 1851-1856] propose another intriguing mechanism that may relieve KLRG1-mediated inhibition in the course of lymphocyte activation. Subsequent to identification of the transferrin receptor (TfR) as a component of a high molecular mass KLRG1 complex, they demonstrate that a fraction of mouse KLRG1 molecules undergoes disulfide-bonding with TfRs and colocalises with the latter at the cell surface. In functional terms, high levels of TfRs such as those found on activated lymphocytes were found to be associated with decreased KLRG1 inhibitory function, indicating that TfRs may sequester KLRG1 from interacting with cadherins. Hence, this unexpected liaison between KLRG1 and TfR may represent a regulatory link between metabolic activation and responses of lymphocytes.

Airway epithelial regulation of pulmonary immune homeostasis and inflammation

Recent genetic, structural and functional studies have identified the airway and lung epithelium as a key orchestrator of the immune response. Further, there is now strong evidence that epithelium dysfunction is involved in the development of inflammatory disorders of the lung. Here we review the characteristic immune responses that are orchestrated by the epithelium in response to diverse triggers such as pollutants, cigarette smoke, bacterial peptides, and viruses. We focus in part on the role of epithelium-derived interleukin (IL)-25, IL-33 and thymic stromal lymphopoietin (TSLP), as well as CC family chemokines as critical regulators of the immune response. We cite examples of the function of the epithelium in host defense and the role of epithelium dysfunction in the development of inflammatory diseases.

IQGAP1: a regulator of intracellular spacetime relativity

Activating and inhibiting receptors of lymphocytes collect valuable information about their mikròs kósmos. This information is essential to initiate or to turn off complex signaling pathways. Irrespective of these advances, our knowledge on how these intracellular activation cascades are coordinated in a spatiotemporal manner is far from complete. Among multiple explanations, the scaffolding proteins have emerged as a critical piece of this evolutionary tangram. Among many, IQGAP1 is one of the essential scaffolding proteins that coordinate multiple signaling pathways. IQGAP1 possesses multiple protein interaction motifs to achieve its scaffolding functions. Using these domains, IQGAP1 has been shown to regulate a number of essential cellular events. This includes actin polymerization, tubulin multimerization, microtubule organizing center formation, calcium/calmodulin signaling, Pak/Raf/Mek1/2-mediated Erk1/2 activation, formation of maestrosome, E-cadherin, and CD44-mediated signaling and glycogen synthase kinase-3/adenomatous polyposis coli-mediated β-catenin activation. In this review, we summarize the recent developments and exciting new findings of cellular functions of IQGAP1.

Cadherin 6 has a functional role in platelet aggregation and thrombus formation

OBJECTIVE

Thrombosis occurs at sites of vascular injury when platelets adhere to subendothelial matrix proteins and to each other. Platelets express many surface receptor proteins, the function of several of these remains poorly characterized. Cadherin 6 is expressed on the platelet surface and contains an arginine-glycine-aspartic acid motif, suggesting that it might have a supportive role in thrombus formation. The aim of this study was to characterize the role of cadherin 6 in platelet function.

METHODS AND RESULTS

Platelet aggregation was inhibited by both antibodies and exogenous soluble cadherin 6. Platelet adhesion to immobilized cadherin 6 was inhibited by arginine-glycine-aspartic acid-serine tetrapeptides. Antibodies to α(IIb)β(3) inhibited platelet adhesion to cadherin 6. Because platelet aggregation occurs in fibrinogen and von Willebrand factor double-deficient mice, we investigated whether cadherin 6 is an alternative ligand for the integrin α(IIb)β(3). Platelet aggregation in fibrinogen and von Willebrand factor double-deficient mice was significantly inhibited by an antibody to cadherin 6. In flow-based assays, inhibition of cadherin 6 caused a marked reduction in thrombus formation in both human and mouse blood.

CONCLUSIONS

This study demonstrates the role of cadherin 6 as a novel ligand for α(IIb)β(3) and highlights its function in thrombus formation.

Regulation and function of the E-cadherin/catenin complex in cells of the monocyte-macrophage lineage and DCs

E-cadherin is best characterized as adherens junction protein, which through homotypic interactions contributes to the maintenance of the epithelial barrier function. In epithelial cells, the cytoplasmic tail of E-cadherin forms a dynamic complex with catenins and regulates several intracellular signal transduction pathways, including Wnt/β-catenin, PI3K/Akt, Rho GTPase, and NF-κB signaling. Recent progress uncovered a novel and critical role for this adhesion molecule in mononuclear phagocyte functions. E-cadherin regulates the maturation and migration of Langerhans cells, and its ligation prevents the induction of a tolerogenic state in bone marrow-derived dendritic cells (DCs). In this respect, the functionality of β-catenin could be instrumental in determining the balance between immunogenicity and tolerogenicity of DCs in vitro and in vivo. Fusion of alternatively activated macrophages and osteoclasts is also E-cadherin-dependent. In addition, the E-cadherin ligands CD103 and KLRG1 are expressed on DC-, T-, and NK-cell subsets and contribute to their interaction with E-cadherin-expressing DCs and macrophages. Here we discuss the regulation, function, and implications of E-cadherin expression in these central orchestrators of the immune system.

E-cadherin expression on human carcinoma cell affects trastuzumab-mediated antibody-dependent cellular cytotoxicity through killer cell lectin-like receptor G1 on natural killer cells

Trastuzumab is a recombinant antibody drug that is widely used for the treatment of HER2-overexpressing breast carcinoma. Despite encouraging clinical results, many HER2-overexpressing carcinomas are primarily resistant to trastuzumab. We attempted to explain trastuzumab resistance and search for solutions. Since the killer cell lectin-like receptor G1 (KLRG1), an inhibitory receptor expressed on subsets of natural killer (NK) cells recognizes E-cadherin as ligands and may inhibit immune responses by regulating the effector function of NK cells, we used HER2-overexpressing carcinoma cells which were expressing E-cadherin to investigate the role of antibody-dependent cellular cytotoxicity (ADCC) through KLRG1 on NK cells in vitro and vivo. The results indicated that HER2-overexpressing carcinoma cells were killed by trastuzumab-mediated ADCC and the ADCC activity was reflected the degree of E-cadherin expression on carcinoma cells. We found that expression of E-cadherin was shown to be a predictor of response to trastuzumab-based treatment for HER2-overexpressing carcinomas, furthermore, trastuzumab-mediated ADCC was markedly enhanced by KLRG1-negative peripheral blood mononuclear cells (PBMCs(KLRG1(-))).

E-cadherin: gatekeeper of airway mucosa and allergic sensitization

The airway epithelium plays a role in immune regulation during environmental challenge, which is intertwined with its barrier function and capacity to limit submucosal access of environmental factors. In asthma, mucosal barrier function is often compromised, with disrupted expression of the adhesion molecule E-cadherin. Recent progress suggests that E-cadherin contributes to the structural and immunological function of airway epithelium, through the regulation of epithelial junctions, proliferation, differentiation, and production of growth factors and proinflammatory mediators that can modulate the immune response. Here, we discuss this novel role for E-cadherin in mediating the crucial immunological decision between maintenance of tolerance versus induction of innate and adaptive immunity.

Once a killer, always a killer: from cytotoxic T cell to memory cell

The control of the differentiation pathways followed by responding CD8(+) T cells to produce protective memory cells has been intensely studied. Recent developments have identified heterogeneity at the effector cytotoxic T-lymphocyte level within which a bona fide memory cell precursor has emerged. The challenge now is to identify the cellular and molecular factors that control this developmental pathway. This review considers aspects of the regulation of the induction of effectors, the transition of effectors to memory cells, and the dynamics of the memory population.