Granzyme B-dependent proteolysis acts as a switch to enhance the proinflammatory activity of IL-1α

Profound loss of esophageal tissue differentiation in patients with eosinophilic esophagitis

BACKGROUND

A key question in the allergy field is to understand how tissue-specific disease is manifested. Eosinophilic esophagitis (EoE) is an emerging tissue-specific allergic disease with an unclear pathogenesis.

OBJECTIVE

Herein we tested the hypothesis that a defect in tissue-specific esophageal genes is an integral part of EoE pathogenesis.

METHODS

We interrogated the pattern of expression of esophagus-specific signature genes derived from the Human Protein Atlas in the EoE transcriptome and in EPC2 esophageal epithelial cells. Western blotting and immunofluorescence were used for evaluating expression of esophageal proteins in biopsy specimens from control subjects and patients with active EoE. Whole-exome sequencing was performed to identify mutations in esophagus-specific genes.

RESULTS

We found that approximately 39% of the esophagus-specific transcripts were altered in patients with EoE, with approximately 90% being downregulated. The majority of transcriptional changes observed in esophagus-specific genes were reproduced in vitro in esophageal epithelial cells differentiated in the presence of IL-13. Functional enrichment analysis revealed keratinization and differentiation as the most affected biological processes and identified IL-1 cytokines and serine peptidase inhibitors as the most dysregulated esophagus-specific protein families in patients with EoE. Accordingly, biopsy specimens from patients with EoE evidenced a profound loss of tissue differentiation, decreased expression of keratin 4 (KRT4) and cornulin (CRNN), and increased expression of KRT5 and KRT14. Whole-exome sequencing of 33 unrelated patients with EoE revealed 39 rare mutations in 18 esophagus-specific differentially expressed genes.

CONCLUSIONS

A tissue-centered analysis has revealed a profound loss of esophageal tissue differentiation (identity) as an integral and specific part of the pathophysiology of EoE and implicated protease- and IL-1-related activities as putative central pathways in disease pathogenesis.

Human S100A7 Induces Mature Interleukin1α Expression by RAGE-p38 MAPK-Calpain1 Pathway in Psoriasis

Psoriatic keratinocytes express exaggerated levels of inflammatory cytokines, and show aberrant hyperproliferation and terminal differentiation in the pathogenesis of psoriasis. The antimicrobial protein hS100A7 (psoriasin) has been found highly expressed in psoriatic skin, but the mechanism and physiological function remain largely unknown. We observed that hS100A7 induces mature interleukin 1α (17kDa) expression in normal human epidermal keratinocytes, which is dependent on RAGE-p38 MAPK and calpain-1 as the inhibitors or knockdown of them completely decreased the expression of mature interleukin1α. Then, we proved mS100a7a15, mature IL-1α and calpain-1 were highly expressed in imquimod-induced psoriasis model and mouse IL-17a-neutralizing antibody treatment attenuated mS100a7a15 expression. At last, PD 151746 (calpain-1 inhibitor) treatment decreased epidermal thickness in imquimod-induced psoriasis model. Taken together, our results suggest that mature IL-1α induced by hS100A7 is via RAGE-p38 MAPK and calpain-1 pathway in keratinocyte and this mechanism may play an important role during psoriasis.

Unconventional Pathways of Secretion Contribute to Inflammation

In the conventional pathway of protein secretion, leader sequence-containing proteins leave the cell following processing through the endoplasmic reticulum (ER) and Golgi body. However, leaderless proteins also enter the extracellular space through mechanisms collectively known as unconventional secretion. Unconventionally secreted proteins often have vital roles in cell and organism function such as inflammation. Amongst the best-studied inflammatory unconventionally secreted proteins are interleukin (IL)-1β, IL-1α, IL-33 and high-mobility group box 1 (HMGB1). In this review we discuss the current understanding of the unconventional secretion of these proteins and highlight future areas of research such as the role of nuclear localisation.

Granzymes A and K differentially potentiate LPS-induced cytokine response

Granzymes are serine proteases that, upon release from cytotoxic cells, induce apoptosis in tumor cells and virally infected cells. In addition, a role of granzymes in inflammation is emerging. Recently, we have demonstrated that extracellular granzyme K (GrK) potentiates lipopolysaccharide (LPS)-induced cytokine response from monocytes. GrK interacts with LPS, disaggregates LPS micelles, and stimulates LPS-CD14 binding and Toll-like receptor signaling. Here we show that human GrA also potentiates cytokine responses in human monocytes initiated by LPS or Gram-negative bacteria. Similar to GrK, this effect is independent of GrA catalytic activity. Unlike GrK, however, GrA does not bind to LPS, has little influence on LPS micelle disaggregation, and does not augment LPS-CD14 complex formation. We conclude that GrA and GrK differentially modulate LPS-Toll-like receptor signaling in monocytes, suggesting functional redundancy among cytotoxic lymphocyte proteases in the anti-bacterial innate immune response.

HMGB1, IL-1α, IL-33 and S100 proteins: dual-function alarmins

Our immune system is based on the close collaboration of the innate and adaptive immune systems for the rapid detection of any threats to the host. Recognition of pathogen-derived molecules is entrusted to specific germline-encoded signaling receptors. The same receptors have now also emerged as efficient detectors of misplaced or altered self-molecules that signal tissue damage and cell death following, for example, disruption of the blood supply and subsequent hypoxia. Many types of endogenous molecules have been shown to provoke such sterile inflammatory states when released from dying cells. However, a group of proteins referred to as alarmins have both intracellular and extracellular functions which have been the subject of intense research. Indeed, alarmins can either exert beneficial cell housekeeping functions, leading to tissue repair, or provoke deleterious uncontrolled inflammation. This group of proteins includes the high-mobility group box 1 protein (HMGB1), interleukin (IL)-1α, IL-33 and the Ca²⁺-binding S100 proteins. These dual-function proteins share conserved regulatory mechanisms, such as secretory routes, post-translational modifications and enzymatic processing, that govern their extracellular functions in time and space. Release of alarmins from mesenchymal cells is a highly relevant mechanism by which immune cells can be alerted of tissue damage, and alarmins play a key role in the development of acute or chronic inflammatory diseases and in cancer development.

Interleukin 1α and the inflammatory process

Inflammation occurs after disruption of tissue homeostasis by cell stress, injury or infection and ultimately involves the recruitment and retention of cells of hematopoietic origin, which arrive at the affected sites to resolve damage and initiate repair. Interleukin 1α (IL-1α) and IL-1β are equally potent inflammatory cytokines that activate the inflammatory process, and their deregulated signaling causes devastating diseases manifested by severe acute or chronic inflammation. Although much attention has been given to understanding the biogenesis of IL-1β, the biogenesis of IL-1α and its distinctive role in the inflammatory process remain poorly defined. In this review we examine key aspects of IL-1α biology and regulation and discuss its emerging importance in the initiation and maintenance of inflammation that underlie the pathology of many human diseases.

Cell death and inflammation: the case for IL-1 family cytokines as the canonical DAMPs of the immune system

It is well known that necrotic cells are capable of promoting inflammation through releasing so-called endogenous 'danger signals' that can promote activation of macrophages, dendritic cells, and other sentinel cells of the innate immune system. However, the identity of these endogenous proinflammatory molecules, also called damage-associated molecular patterns (DAMPs), has been debated since the 'danger model' was first advanced 20 years ago. While a relatively large number of molecules have been proposed to act as DAMPs, little consensus has emerged concerning which of these represent the key activators of sterile inflammation. Here I argue that the canonical DAMPs have long been hiding in plain sight, in the form of members of the extended IL-1 cytokine family (IL-1α, IL-1β, IL-18, IL-33, IL-36α, IL-36β, and IL-36γ). The latter cytokines possess all of the characteristics expected of endogenous DAMPs and initiate inflammation in a manner strikingly similar to that utilized by the other major category of inflammatory triggers, pathogen-associated molecular patterns (PAMPs). Furthermore, many PAMPs upregulate the expression of IL-1 family DAMPs, enabling robust synergy between these distinct classes of inflammatory triggers. Thus, multiple lines of evidence now suggest that IL-1 family cytokines represent the key initiators of necrosis-initiated sterile inflammation, as well as amplifiers of inflammation in response to infection-associated tissue injury.

Senescence in chronic allograft nephropathy

Despite increasing numbers of patients on dialysis, the numbers of renal transplants performed yearly have remained relatively static. During the last 50 years, there have been many advances in the pharmacology of prevention of organ rejection. However, most patients will suffer from a slow but steady decline in renal function leading to graft loss. The most common cause of long-term graft loss is chronic allograft nephropathy (CAN). Therefore, elucidating and understanding the mechanisms involved in CAN is crucial for achieving better posttransplant outcomes. It is thought that the development of epithelial to mesenchymal transition (EMT) in proximal tubules is one of the first steps towards CAN, and has been shown to be a result of cellular senescence. Cells undergoing senescence acquire a senescence associated secretory phenotype (SASP) leading to the production of interleukin-1 alpha (IL-1α), which has been implicated in several degenerative and inflammatory processes including renal disease. A central mediator in SASP activation is the production of reactive oxygen species (ROS), which are produced in response to numerous physiological and pathological stimuli. This review explores the connection between SASP and the development of EMT/CAN in an effort to suggest future directions for research leading to improved long-term graft outcomes.

Neutrophil Elastase-mediated proteolysis activates the anti-inflammatory cytokine IL-36 Receptor antagonist

The interleukin-36 receptor antagonist (IL-36Ra) which regulates IL-36α, -β and -γ is linked to psoriatic inflammation, especially loss-of-function mutations in pustular psoriasis subtypes. As observed with other IL-1 superfamily proteins, the IL-36 members require N-terminal cleavage for full biological activity but the mechanisms of IL-36Ra activation remain poorly defined. Using different blood leukocyte and skin resident cell preparations, and recombinant proteins, we have identified that neutrophil elastase, but not other neutrophil derived proteases, cleaves IL-36Ra into its highly active antagonistic form. The activity of this processed form of IL-36Ra was confirmed in human primary dermal fibroblasts and keratinocytes and in skin equivalents. A significant dose dependent reduction of IL-36γ induced IL-8 and chemokine ligand 20 (CCL20) levels were detected following addition of the cleaved IL-36Ra compared to full length IL-36Ra. By activating IL-36Ra, the neutrophil derived protease can inhibit IL-36 induced chemokine production, including IL-8 and CCL20, and reduce further inflammatory cell infiltration. These findings strongly indicate neutrophil elastase to be a key enzyme in the biological function of IL-36Ra and that neutrophils can play a regulatory role in psoriatic inflammation with regard to balancing the pro-inflammatory activity of IL-36.

The Inflammasome and the Epidermal Growth Factor Receptor (EGFR) Are Involved in the Staphylococcus aureus-Mediated Induction of IL-1alpha and IL-1beta in Human Keratinocytes

Staphylococcus (S.) aureus is an important pathogen causing various infections including those of the skin. Keratinocytes are able to sense invading S. aureus and to initiate a fast defense reaction by the rapid release of innate defense mediators such as antimicrobial peptides and cytokines. There is increasing evidence that the cytokines IL-1alpha and IL-1beta, which both signal through the IL-1 receptor, play an important role in cutaneous defense against S. aureus. The aim of this study was to gain more insight into the underlying mechanisms leading to the S. aureus-induced IL-1alpha and IL-1beta expression in keratinocytes. Infection of human primary keratinocytes with S. aureus led to the induction of gene expression and protein secretion of IL-1alpha and IL-1beta. Full S. aureus-induced IL-1 protein release required the inflammasome components caspase-1 and ASC (apoptosis-associated speck-like protein containing a CARD) whereas gene induction of IL-1alpha and IL-beta by S. aureus was not dependent on caspase-1 and ASC. Since patients receiving anti-cancer therapy by inhibition of the epidermal growth factor receptor (EGFR) often suffer from skin infections caused by S. aureus we additionally evaluated whether the EGFR pathway may be involved in the IL-1alpha and IL-1beta induction by S. aureus. Inactivation of the EGFR with a blocking antibody decreased the S. aureus-mediated IL-1alpha and IL-1beta induction in primary keratinocytes. Moreover, the use of siRNA experiments revealed that ADAM17 (A Disintegrin and A Metalloprotease 17), a metalloproteinase known to mediate the shedding and release of EGFR ligands, was required for full induction of IL-1alpha and IL-1beta in keratinocytes infected with S. aureus. A failure of keratinocytes to adequately upregulate IL-1alpha and IL-1beta may promote S. aureus skin infections.

IL-1α Gene Deletion Protects Oligodendrocytes after Spinal Cord Injury through Upregulation of the Survival Factor Tox3

Spinal cord injury (SCI) causes the release of danger signals by stressed and dying cells, a process that leads to neuroinflammation. Evidence suggests that inflammation plays a role in both the damage and repair of injured neural tissue. We show that microglia at sites of SCI rapidly express the alarmin interleukin (IL)-1α, and that infiltrating neutrophils and macrophages subsequently produce IL-1β. Infiltration of these cells is dramatically reduced in both IL-1α(-/-) and IL-1β(-/-) mice, but only IL-1α(-/-) mice showed rapid (at day 1) and persistent improvements in locomotion associated with reduced lesion volume. Similarly, intrathecal administration of the IL-1 receptor antagonist anakinra restored locomotor function post-SCI. Transcriptome analysis of SCI tissue at day 1 identified the survival factor Tox3 as being differentially regulated exclusively in IL-1α(-/-) mice compared with IL-1β(-/-) and wild-type mice. Accordingly, IL-1α(-/-) mice have markedly increased Tox3 levels in their oligodendrocytes, beginning at postnatal day 10 (P10) and persisting through adulthood. At P10, the spinal cord of IL-1α(-/-) mice showed a transient increase in mature oligodendrocyte numbers, coinciding with increased IL-1α expression in wild-type animals. In adult mice, IL-1α deletion is accompanied by increased oligodendrocyte survival after SCI. TOX3 overexpression in human oligodendrocytes reduced cellular death under conditions mimicking SCI. These results suggest that IL-1α-mediated Tox3 suppression during the early phase of CNS insult plays a crucial role in secondary degeneration.

SIGNIFICANCE STATEMENT

The mechanisms underlying bystander degeneration of neurons and oligodendrocytes after CNS injury are ill defined. We show that microglia at sites of spinal cord injury (SCI) rapidly produce the danger signal interleukin (IL)-1α, which triggers neuroinflammation and locomotor defects. We uncovered that IL-1α(-/-) mice have markedly increased levels of the survival factor Tox3 in their oligodendrocytes, which correlates with the protection of this cell population, and reduced lesion volume, resulting in unprecedented speed, level, and persistence of functional recovery after SCI. Our data suggest that central inhibition of IL-1α or Tox3 overexpression during the acute phase of a CNS insult may be an effective means for preventing the loss of neurological function in SCI, or other acute injuries such as ischemia and traumatic brain injuries.

Interleukin-1α Activity in Necrotic Endothelial Cells Is Controlled by Caspase-1 Cleavage of Interleukin-1 Receptor-2: IMPLICATIONS FOR ALLOGRAFT REJECTION

Inflammation is a key instigator of the immune responses that drive atherosclerosis and allograft rejection. IL-1α, a powerful cytokine that activates both innate and adaptive immunity, induces vessel inflammation after release from necrotic vascular smooth muscle cells (VSMCs). Similarly, IL-1α released from endothelial cells (ECs) damaged during transplant drives allograft rejection. However, IL-1α requires cleavage for full cytokine activity, and what controls cleavage in necrotic ECs is currently unknown. We find that ECs have very low levels of IL-1α activity upon necrosis. However, TNFα or IL-1 induces significant levels of active IL-1α in EC necrotic lysates without alteration in protein levels. Increased activity requires cleavage of IL-1α by calpain to the more active mature form. Immunofluorescence and proximity ligation assays show that IL-1α associates with interleukin-1 receptor-2, and this association is decreased by TNFα or IL-1 and requires caspase activity. Thus, TNFα or IL-1 treatment of ECs leads to caspase proteolytic activity that cleaves interleukin-1 receptor-2, allowing IL-1α dissociation and subsequent processing by calpain. Importantly, ECs could be primed by IL-1α from adjacent damaged VSMCs, and necrotic ECs could activate neighboring normal ECs and VSMCs, causing them to release inflammatory cytokines and up-regulate adhesion molecules, thus amplifying inflammation. These data unravel the molecular mechanisms and interplay between damaged ECs and VSMCs that lead to activation of IL-1α and, thus, initiation of adaptive responses that cause graft rejection.

Interleukin-1 as a pharmacological target in acute brain injury

NEW FINDINGS

What is the topic of this review? This review discusses the latest findings on the contribution of inflammation to brain injury, how inflammation is a therapeutic target, and details of recent and forthcoming clinical studies. What advances does it highlight? Here we highlight recent advances on the role and regulation of inflammasomes, and the latest clinical progress in targeting inflammation. Acute brain injury is one of the leading causes of mortality and disability worldwide. Despite this, treatments for acute brain injuries are limited, and there remains a massive unmet clinical need. Inflammation has emerged as a major contributor to non-communicable diseases, and there is now substantial and growing evidence that inflammation, driven by the cytokine interleukin-1 (IL-1), worsens acute brain injury. Interleukin-1 is regulated by large, multimolecular complexes called inflammasomes. Here, we discuss the latest research on the regulation of inflammasomes and IL-1 in the brain, preclinical efforts to establish the IL-1 system as a therapeutic target, and the promise of recent and future clinical studies on blocking the action of IL-1 for the treatment of brain injury.

The interleukin (IL)-1 cytokine family--Balance between agonists and antagonists in inflammatory diseases

The interleukin (IL)-1 family of cytokines comprises 11 members, including 7 pro-inflammatory agonists (IL-1α, IL-1β, IL-18, IL-33, IL-36α, IL-36β, IL-36γ) and 4 defined or putative antagonists (IL-1R antagonist (IL-1Ra), IL-36Ra, IL-37, and IL-38) exerting anti-inflammatory activities. Except for IL-1Ra, IL-1 cytokines do not possess a leader sequence and are secreted via an unconventional pathway. In addition, IL-1β and IL-18 are produced as biologically inert pro-peptides that require cleavage by caspase-1 in their N-terminal region to generate active proteins. N-terminal processing is also required for full activity of IL-36 cytokines. The IL-1 receptor (IL-1R) family comprises 10 members and includes cytokine-specific receptors, co-receptors and inhibitory receptors. The signaling IL-1Rs share a common structure with three extracellular immunoglobulin (Ig) domains and an intracellular Toll-like/IL-1R (TIR) domain. IL-1 cytokines bind to their specific receptor, which leads to the recruitment of a co-receptor and intracellular signaling. IL-1 cytokines induce potent inflammatory responses and their activity is tightly controlled at the level of production, protein processing and maturation, receptor binding and post-receptor signaling by naturally occurring inhibitors. Some of these inhibitors are IL-1 family antagonists, while others are IL-1R family members acting as membrane-bound or soluble decoy receptors. An imbalance between agonist and antagonist levels can lead to exaggerated inflammatory responses. Several genetic modifications or mutations associated with dysregulated IL-1 activity and autoinflammatory disorders were identified in mouse models and in patients. These findings paved the road to the successful use of IL-1 inhibitors in diseases that were previously considered as untreatable.

TOE1 is an inhibitor of HIV-1 replication with cell-penetrating capability

Target of Egr1 (TOE1) is a nuclear protein localized primarily in nucleoli and Cajal bodies that was identified as a downstream target of the immediate early gene Egr1. TOE1 displays a functional deadenylation domain and has been shown to participate in spliceosome assembly. We report here that TOE1 can function as an inhibitor of HIV-1 replication and show evidence that supports a direct interaction of TOE1 with the viral specific transactivator response element as part of the inhibitory mechanism. In addition, we show that TOE1 can be secreted by activated CD8(+) T lymphocytes and can be cleaved by the serine protease granzyme B, one of the main components of cytotoxic granules. Both full-length and cleaved TOE1 can spontaneously cross the plasma membrane and penetrate cells in culture, retaining HIV-1 inhibitory activity. Antiviral potency of TOE1 and its cell-penetrating capability have been identified to lie within a 35-amino-acid region containing the nuclear localization sequence.

Diverse Activators of the NLRP3 Inflammasome Promote IL-1β Secretion by Triggering Necrosis

The NLRP3 inflammasome is involved in caspase-1-dependent maturation of IL-1β in many contexts. A two-signal model has emerged for IL-1β maturation, with LPS providing "signal I" and diverse agents such as ATP, Nigericin, streptolysin O, uric acid crystals, and alum salts capable of acting as "signal II." In the absence of signal II, pro-IL-1β is upregulated but typically fails to be processed or released. What unites signal II stimuli has been debated, with the ability to promote K+ efflux suggested as a common factor, but the mechanism of IL-1β release remains unclear. Here, we show that all examined inflammasome signal II agents triggered necrosis, which was highly correlated with their ability to promote IL-1β release. IL-1β secretion occurred in tandem with the release of many additional proteins and was confined to necrotic cells. Thus, signal II agents initiate inflammation by promoting necrosis-driven IL-1β release, suggesting that IL-1β represents an inducible danger signal.

Interleukin-1α and brain inflammation

Acute brain injuries such as caused by stroke are amongst the leading causes of death and are the leading cause of disability. Despite this there are very limited therapeutic options, and new therapeutic strategies and targets are required. Inflammation is known to exacerbate brain injury and is now considered as a potential therapeutic target. The damaging inflammation that occurs after acute brain injury is driven by pro-inflammatory members of the interleukin (IL)-1 cytokine family, namely, IL-1α and IL-1β. Previous research efforts have focussed on the biology and contribution of IL-1β. However, we now recognise that IL-1α is an early and important mediator of inflammation after injury. This review focuses on what is known about IL-1α, its regulation and its contribution to brain injury. Inhibiting mechanisms regulating the processing and release of IL-1α may offer new therapeutic targets for the treatment of devastating acute brain injuries.

Interleukin-1α activation and localization in lipopolysaccharide-stimulated human monocytes and macrophages

BACKGROUND

Interleukin-1α (IL-1α) is a proinflammatory cytokine belonging to the IL-1 family. It is synthesized as a 33kDa precursor peptide that is cleaved by a calpain-like protease to a 16 kDa propiece and a 17 kDa mature IL-1α peptide. In contrast to its close relative, IL-1β, the role of IL-1α in inflammation is only partly understood.

RESULTS

Human monocyte derived macrophages, stimulated with lipopolysaccharide (LPS) were analysed for production and localization of IL-1α by use of a monoclonal antibody (MAb) generated against recombinant precursor IL-1α. We found that the MAb detected IL-1α within the nuclei of the cells 2h (hours) after LPS stimulation and production continued for up to 20 h. At no time could we demonstrate cleavage of the IL-1α precursor. The MAb was conjugated to fluorescein isothiocyanate (FITC) for use in flow cytometry. Based on the flow cytometric analysis CD68 positive cells were positive for IL-1α in agreement with CD68 being a marker for monocytes.

CONCLUSIONS

Here, we demonstrate, for the first time, a method to visualize and measure the production of IL-1α in both human monocytes and macrophages.

Granzyme B-expressing neutrophils correlate with bacterial load in granulomas from Mycobacterium tuberculosis-infected cynomolgus macaques

The role of neutrophils in tuberculosis (TB), and whether neutrophils express granzyme B (grzB), a pro-apoptotic enzyme associated with cytotoxic T cells, is controversial. We examined neutrophils in peripheral blood (PB) and lung granulomas of Mycobacterium tuberculosis-infected cynomolgus macaques and humans to determine whether mycobacterial products or pro-inflammatory factors induce neutrophil grzB expression. We found large numbers of grzB-expressing neutrophils in macaque and human granulomas and these cells contained more grzB+ granules than T cells. Higher neutrophil, but not T cell, grzB expression correlated with increased bacterial load. Although unstimulated PB neutrophils lacked grzB expression, grzB expression increased upon exposure to M.tuberculosis bacilli, M.tuberculosis culture filtrate protein or lipopolysaccharide from Escherichia coli. Perforin is required for granzyme-mediated cytotoxicity by T cells, but was not observed in PB or granuloma neutrophils. Nonetheless, stimulated PB neutrophils secreted grzB as determined by enzyme-linked immunospot assays. Purified grzB was not bactericidal or bacteriostatic, suggesting secreted neutrophil grzB acts on extracellular targets, potentially enhancing neutrophil migration through extracellular matrix and regulating apoptosis or activation in other cell types. These data indicate mycobacterial products and the pro-inflammatory environment of granulomas up-regulates neutrophil grzB expression and suggests a previously unappreciated aspect of neutrophil biology in TB.

Granzymes regulate proinflammatory cytokine responses

Granzymes (Grs) are serine proteases mainly produced by cytotoxic lymphocytes and are traditionally considered to cause apoptosis in tumor cells and virally infected cells. However, the cytotoxicity of several Grs is currently being debated, and additional, predominantly extracellular, functions of Grs in inflammation are emerging. Extracellular soluble Grs are elevated in the circulation of patients with autoimmune diseases and infections. Additionally, Grs are expressed by several types of immune cells other than cytotoxic lymphocytes. Recent research has revealed novel immunomodulatory functions of Grs. In this review, we provide a comprehensive overview on the role of Grs in inflammation, highlighting their role in cytokine induction and processing.

Granzyme B expression is enhanced in human monocytes by TLR8 agonists and contributes to antibody-dependent cellular cytotoxicity

FcγRs are critical mediators of mAb cancer therapies, because they drive cytotoxic processes upon binding of effector cells to opsonized targets. Along with NK cells, monocytes are also known to destroy Ab-coated targets via Ab-dependent cellular cytotoxicity (ADCC). However, the precise mechanisms by which monocytes carry out this function have remained elusive. In this article, we show that human monocytes produce the protease granzyme B upon both FcγR and TLR8 activation. Treatment with TLR8 agonists elicited granzyme B and also enhanced FcγR-mediated granzyme B production in an additive fashion. Furthermore, monocyte-mediated ADCC against cetuximab-coated tumor targets was enhanced by TLR8 agonist treatment, and this enhancement of ADCC required granzyme B. Hence we have identified granzyme B as an important mediator of FcγR function in human monocytes and have uncovered another mechanism by which TLR8 agonists may enhance FcγR-based therapies.

Granzyme-mediated regulation of host defense in the liver in experimental Leishmania donovani infection

In the livers of susceptible C57BL/6 (B6) mice infected with Leishmania donovani, CD8(+) T cell mechanisms are required for granuloma assembly, macrophage activation, intracellular parasite killing, and self-cure. Since gene expression of perforin and granzymes A and B (GzmA and GzmB), cytolytic proteins linked to CD8(+) cell effector function, was enhanced in infected liver tissue, B6 mice deficient in these granular proteins were used to gauge host defense roles. Neither perforin nor GzmA was required; however, mice deficient in GzmB (GzmB(-/-), GzmB cluster(-/-), and GzmA×B cluster double knockout [DKO] mice) showed both delayed granuloma assembly and initially impaired control of parasite replication. Since these two defects in B6 mice were limited to early-stage infection, innately resistant 129/Sv mice were also tested. In this genetic setting, expression of both innate and subsequent T (Th1) cell-dependent acquired resistance, including the self-cure phenotype, was entirely derailed in GzmA×B cluster DKO mice. These results, in susceptible B6 mice for GzmB and in resistant 129/Sv mice for GzmA and/or the GzmB cluster, point to granzyme-mediated host defense regulation in the liver in experimental visceral leishmaniasis.

Granzyme B promotes cytotoxic lymphocyte transmigration via basement membrane remodeling

Granzyme B (GzmB) is a protease with a well-characterized intracellular role in targeted destruction of compromised cells by cytotoxic lymphocytes. However, GzmB also cleaves extracellular matrix components, suggesting that it influences the interplay between cytotoxic lymphocytes and their environment. Here, we show that GzmB-null effector T cells and natural killer (NK) cells exhibited a cell-autonomous homing deficit in mouse models of inflammation and Ectromelia virus infection. Intravital imaging of effector T cells in inflamed cremaster muscle venules revealed that GzmB-null cells adhered normally to the vessel wall and could extend lamellipodia through it but did not cross it efficiently. In vitro migration assays showed that active GzmB was released from migrating cytotoxic lymphocytes and enabled chemokine-driven movement through basement membranes. Finally, proteomic analysis demonstrated that GzmB cleaved basement membrane constituents. Our results highlight an important role for GzmB in expediting cytotoxic lymphocyte diapedesis via basement membrane remodeling.

Cytokines and mucosal immunity

PURPOSE OF REVIEW

Cytokines are integral mediators for maintaining intestinal mucosal homeostasis, as well as prominent effector molecules during chronic gut inflammatory diseases. This review focuses on recent studies of the role of specific cytokines in mucosal immunity.

RECENT FINDINGS

Dichotomous, or even opposing, functions have been described for several cytokines involved in intestinal innate immunity (most notably for members of the interleukin-1 family), which depend on the specific inflammatory conditions within the intestinal mucosa. For example, both interleukin-1α and interleukin-33 exhibit 'alarmin'-type properties that can signal tissue or cell damage, which further add to their well described proinflammatory roles. Costimulatory molecules of the tumor necrosis factor/tumor necrosis factor receptor superfamily, such as TNF-like cytokine 1A and LIGHT, are actively involved in mucosal proinflammatory pathways, but also may exert protection against infectious agents to facilitate recovery from acute inflammation. Finally, innate lymphoid cells are increasingly recognized as important cellular sources of pivotal mucosal cytokines, including the interleukin-23/T helper 17 cytokine, interleukin-22.

SUMMARY

Elucidating the complexity of cytokine signaling within the normal mucosa and during acute and chronic inflammation will be a pivotal step toward understanding the pathogenesis of immune-mediated gut diseases and developing effective therapies to treat them.

Cytokine pathways regulating glial and leukocyte function after spinal cord and peripheral nerve injury

Injury to the nervous system causes the almost immediate release of cytokines by glial cells and neurons. These cytokines orchestrate a complex array of responses leading to microgliosis, immune cell recruitment, astrogliosis, scarring, and the clearance of cellular debris, all steps that affect neuronal survival and repair. This review will focus on cytokines released after spinal cord and peripheral nerve injury and the primary signalling pathways triggered by these inflammatory mediators. Notably, the following cytokine families will be covered: IL-1, TNF, IL-6-like, TGF-β, and IL-10. Whether interfering with cytokine signalling could lead to novel therapies will also be discussed. Finally, the review will address whether manipulating the above-mentioned cytokine families and signalling pathways could exert distinct effects in the injured spinal cord versus peripheral nerve.

The IL-1 family in fish: swimming through the muddy waters of inflammasome evolution

Inflammatory diseases are a significant burden on global healthcare systems, and tackling these diseases is a major focus of modern medicine. Key to many inflammatory diseases is the cytokine, Interleukin-1 (IL-1). Due to its apical role in initiating the inflammatory response, dysregulated IL-1 signalling results in a number of pathologies. Treatment of inflammatory diseases with anti-IL-1 therapies has offered many therapeutic benefits, however current therapies are protein based, with all the accompanying limitations. The non-conventional pathways involved in IL-1 signalling provide a number of potential therapeutic targets for clinical intervention and this has led to the exploitation of a number of model organisms for the study of IL-1 biology. Murine models have long been used to study IL-1 processing and release, but do not allow direct visualisation in vivo. Recently, fish models have emerged as genetically tractable and optically transparent inflammatory disease models. These models have raised questions on the evolutionary origins of the IL-1 family and the conservation in its processing and activation. Here we review the current understanding of IL-1 evolution in fish and discuss the study of IL-1 processing in these models.

Persistent release of IL-1s from skin is associated with systemic cardio-vascular disease, emaciation and systemic amyloidosis: the potential of anti-IL-1 therapy for systemic inflammatory diseases

The skin is an immune organ that contains innate and acquired immune systems and thus is able to respond to exogenous stimuli producing large amount of proinflammatory cytokines including IL-1 and IL-1 family members. The role of the epidermal IL-1 is not limited to initiation of local inflammatory responses, but also to induction of systemic inflammation. However, association of persistent release of IL-1 family members from severe skin inflammatory diseases such as psoriasis, epidermolysis bullosa, atopic dermatitis, blistering diseases and desmoglein-1 deficiency syndrome with diseases in systemic organs have not been so far assessed. Here, we showed the occurrence of severe systemic cardiovascular diseases and metabolic abnormalities including aberrant vascular wall remodeling with aortic stenosis, cardiomegaly, impaired limb and tail circulation, fatty tissue loss and systemic amyloid deposition in multiple organs with liver and kidney dysfunction in mouse models with severe dermatitis caused by persistent release of IL-1s from the skin. These morbid conditions were ameliorated by simultaneous administration of anti-IL-1α and IL-1β antibodies. These findings may explain the morbid association of arteriosclerosis, heart involvement, amyloidosis and cachexia in severe systemic skin diseases and systemic autoinflammatory diseases, and support the value of anti-IL-1 therapy for systemic inflammatory diseases.

Serine protease inhibition attenuates rIL-12-induced GZMA activity and proinflammatory events by modulating the Th2 profile from estrogen-treated mice

Estrogen has potent immunomodulatory effects on proinflammatory responses, which can be mediated by serine proteases. We now demonstrate that estrogen increased the extracellular expression and IL-12-induced activity of a critical member of serine protease family Granzyme A, which has been shown to possess a novel inflammatory persona. The inhibition of serine protease activity with inhibitor 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride significantly diminished enhanced production of proinflammatory interferon-γ, IL-1β, IL-1α, and Granzyme A activity even in the presence of a Th1-inducing cytokine, IL-12 from splenocytes from in vivo estrogen-treated mice. Inhibition of serine protease activity selectively promoted secretion of Th2-specific IL-4, nuclear phosphorylated STAT6A, signal transducer and activator of transcription (STAT)6A translocation, and STAT6A DNA binding in IL-12-stimulated splenocytes from estrogen-treated mice. Inhibition with 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride reversed the down-regulation of Th2 transcription factors, GATA3 and c-Maf in splenocytes from estrogen-exposed mice. Although serine protease inactivation enhanced the expression of Th2-polarizing factors, it did not reverse estrogen-modulated decrease of phosphorylated STAT5, a key factor in Th2 development. Collectively, data suggest that serine protease inactivity augments the skew toward a Th2-like profile while down-regulating IL-12-induced proinflammatory Th1 biomolecules upon in vivo estrogen exposure, which implies serine proteases as potential regulators of inflammation. Thus, these studies may provide a potential mechanism underlying the immunomodulatory effect of estrogen and insight into new therapeutic strategies for proinflammatory and female-predominant autoimmune diseases.

Granzyme B releases vascular endothelial growth factor from extracellular matrix and induces vascular permeability

The formation of unstable, leaky neovessels underlies the pathogenesis of many chronic inflammatory diseases. Granzyme B (GZMB) is an immune-derived serine protease that accumulates in the extracellular matrix (ECM) during chronic inflammation and is capable of cleaving fibronectin (FN). Vascular endothelial growth factor (VEGF) is a potent vascular permeabilizing agent that is sequestered in the ECM through its interaction with FN. As GZMB levels are elevated in chronic inflammatory diseases that are associated with increased vascular permeability, the role of GZMB in the regulation of VEGF bioavailability and vascular permeability were assessed. GZMB was added to either VEGF bound to FN or VEGF bound to endothelial cell (EC)-derived ECM. Supernatants containing released VEGF were assessed to determine VEGF activity by treating EC and evaluating VEGF receptor-2 (VEGFR2) phosphorylation. GZMB released VEGF from both FN and from EC-derived matrix, whereas GZMB inhibition prevented FN cleavage and VEGF release. GZMB-mediated VEGF release resulted in significant phosphorylation of VEGFR2. The role of GZMB-mediated VEGF release in altering vascular permeability was also assessed in vivo using Miles/Evans blue permeability assay. GZMB induced a significant VEGF-dependent increase in vascular permeability in vivo that was reduced in the presence of an anti-VEGF-neutralizing antibody. Inflammatory-mediated vascular leakage was also assessed in GZMB-KO mice using a delayed-type hypersensitivity model. GZMB-KO mice exhibited reduced microvascular leakage compared with C57\B6 controls. GZMB increases vascular permeability in part through the proteolytic release of ECM-sequestered VEGF, leading to VEGFR2 activation and increased vascular permeability in vivo. These findings present a novel role for GZMB as a modulator of vascular response during chronic inflammation.

Release of interleukin-1α or interleukin-1β depends on mechanism of cell death

The cytokine interleukin-1 (IL-1) has two main pro-inflammatory forms, IL-1α and IL-1β, which are central to host responses to infection and to damaging sterile inflammation. Processing of IL-1 precursor proteins to active cytokines commonly occurs through activation of proteases, notably caspases and calpains. These proteases are instrumental in cell death, and inflammation and cell death are closely associated, hence we sought to determine the impact of cell death pathways on IL-1 processing and release. We discovered that apoptotic regulation of caspase-8 specifically induced the processing and release of IL-1β. Conversely, necroptosis caused the processing and release of IL-1α, and this was independent of IL-1β processing and release. These data suggest that the mechanism through which an IL-1-expressing cell dies dictates the nature of the inflammatory mechanism that follows. These insights may allow modification of inflammation through the selective targeting of cell death mechanisms during disease.

In vitro evaluation of a soluble Leishmania promastigote surface antigen as a potential vaccine candidate against human leishmaniasis

PSA (Promastigote Surface Antigen) belongs to a family of membrane-bound and secreted proteins present in several Leishmania (L.) species. PSA is recognized by human Th1 cells and provides a high degree of protection in vaccinated mice. We evaluated humoral and cellular immune responses induced by a L. amazonensis PSA protein (LaPSA-38S) produced in a L. tarentolae expression system. This was done in individuals cured of cutaneous leishmaniasis due to L. major (CCLm) or L. braziliensis (CCLb) or visceral leishmaniasis due to L. donovani (CVLd) and in healthy individuals. Healthy individuals were subdivided into immune (HHR-Lm and HHR-Li: Healthy High Responders living in an endemic area for L. major or L. infantum infection) or non immune/naive individuals (HLR: Healthy Low Responders), depending on whether they produce high or low levels of IFN-γ in response to Leishmania soluble antigen. Low levels of total IgG antibodies to LaPSA-38S were detected in sera from the studied groups. Interestingly, LaPSA-38S induced specific and significant levels of IFN-γ, granzyme B and IL-10 in CCLm, HHR-Lm and HHR-Li groups, with HHR-Li group producing TNF-α in more. No significant cytokine response was observed in individuals immune to L. braziliensis or L. donovani infection. Phenotypic analysis showed a significant increase in CD4+ T cells producing IFN-γ after LaPSA-38S stimulation, in CCLm. A high positive correlation was observed between the percentage of IFN-γ-producing CD4+ T cells and the released IFN-γ. We showed that the LaPSA-38S protein was able to induce a mixed Th1 and Th2/Treg cytokine response in individuals with immunity to L. major or L. infantum infection indicating that it may be exploited as a vaccine candidate. We also showed, to our knowledge for the first time, the capacity of Leishmania PSA protein to induce granzyme B production in humans with immunity to L. major and L. infantum infection.

Granzyme K synergistically potentiates LPS-induced cytokine responses in human monocytes

Granzymes are serine proteases released by cytotoxic lymphocytes to induce apoptosis in virus-infected cells and tumor cells. Evidence is emerging that granzymes also play a role in controlling inflammation. Granzyme serum levels are elevated in patients with autoimmune diseases and infections, including sepsis. However, the function of extracellular granzymes in inflammation largely remains unknown. Here, we show that granzyme K (GrK) binds to Gram-negative bacteria and their cell-wall component lipopolysaccharide (LPS). GrK synergistically enhances LPS-induced cytokine release in vitro from primary human monocytes and in vivo in a mouse model of LPS challenge. Intriguingly, these extracellular effects are independent of GrK catalytic activity. GrK disaggregates LPS from micelles and augments LPS-CD14 complex formation, thereby likely boosting monocyte activation by LPS. We conclude that extracellular GrK is an unexpected direct modulator of LPS-TLR4 signaling during the antimicrobial innate immune response.

Non-redundant properties of IL-1α and IL-1β during acute colon inflammation in mice

OBJECTIVE

The differential role of the IL-1 agonists, IL-1α, which is mainly cell-associated versus IL-1β, which is mostly secreted, was studied in colon inflammation.

DESIGN

Dextran sodium sulfate (DSS) colitis was induced in mice globally deficient in either IL-1α or IL-1β, and in wild-type mice, or in mice with conditional deletion of IL-1α in intestinal epithelial cells (IECs). Bone marrow transplantation experiments were performed to assess the role of IL-1α or IL-1β of myeloid versus colon non-hematopoietic cells in inflammation and repair in acute colitis.

RESULTS

IL-1α released from damaged IECs acts as an alarmin by initiating and propagating colon inflammation, as IL-1α deficient mice exhibited mild disease symptoms with improved recovery. IL-1β is involved in repair of IECs and reconstitution of the epithelial barrier during the resolution of colitis; its deficiency correlates with disease exacerbation. Neutralisation of IL-1α in control mice during acute colitis led to alleviation of clinical and histological manifestations, whereas treatment with rIL-1Ra or anti-IL-1β antibodies was not effective. Repair after colitis correlated with accumulation of CD8 and regulatory T cells in damaged crypts.

CONCLUSIONS

The role of IL-1α and IL-1β differs in DSS-induced colitis in that IL-1α, mainly of colon epithelial cells is inflammatory, whereas IL-1β, mainly of myeloid cell origin, promotes healing and repair. Given the dissimilar functions of each IL-1 agonistic molecule, an IL-1 receptor blockade would not be as therapeutically effective as specific neutralising of IL-1α, which leaves IL-1β function intact.

The role IL-1 in tumor-mediated angiogenesis

Tumor angiogenesis is one of the hallmarks of tumor progression and is essential for invasiveness and metastasis. Myeloid inflammatory cells, such as immature myeloid precursor cells, also termed myeloid-derived suppressor cells (MDSCs), neutrophils, and monocytes/macrophages, are recruited to the tumor microenvironment by factors released by the malignant cells that are subsequently “educated” in situ to acquire a pro-invasive, pro-angiogenic, and immunosuppressive phenotype. The proximity of myeloid cells to endothelial cells (ECs) lining blood vessels suggests that they play an important role in the angiogenic response, possibly by secreting a network of cytokines/chemokines and inflammatory mediators, as well as via activation of ECs for proliferation and secretion of pro-angiogenic factors. Interleukin-1 (IL-1) is an “alarm,” upstream, pro-inflammatory cytokine that is generated primarily by myeloid cells. IL-1 initiates and propagates inflammation, mainly by inducing a local cytokine network and enhancing inflammatory cell infiltration to affected sites and by augmenting adhesion molecule expression on ECs and leukocytes. Pro-inflammatory mediators were recently shown to play an important role in tumor-mediated angiogenesis and blocking their function may suppress tumor progression. In this review, we summarize the interactions between IL-1 and other pro-angiogenic factors during normal and pathological conditions. In addition, the feasibility of IL-1 neutralization approaches for anti-cancer therapy is discussed.

The inflammasomes in autoinflammatory diseases with skin involvement

During the past years, significant progress in the understanding of the complexity, regulation, and relevance of innate immune responses underlying several inflammatory conditions with neutrophilic skin involvement has been made. These diseases belong to the novel class of autoinflammatory diseases, and several are caused by mutations in genes regulating the function of innate immune complexes, termed inflammasomes, leading to enhanced secretion of the proinflammatory cytokine IL-1β. Consequently, targeting of IL-1β has proven successful in the treatment of these diseases, and the identification of related pathogenic mechanisms in other more common skin diseases characterized by autoinflammation and neutrophilic tissue damage also provides extended opportunities for therapy by interfering with IL-1 signaling.

Are all granzymes cytotoxic in vivo?

Granzymes are serine proteases mainly found in cytotoxic lymphocytes. The most-studied member of this group is granzyme B, which is a potent cytotoxin that has set the paradigm that all granzymes are cyototoxic. In the last 5 years, this paradigm has become controversial. On one hand, there is a plethora of sometimes contradictory publications showing mainly caspase-independent cytotoxic effects of granzyme A and the so-called orphan granzymes in vitro. On the other hand, there are increasing numbers of reports of granzymes failing to induce cell death in vitro unless very high (potentially supra-physiological) concentrations are used. Furthermore, experiments with granzyme A or granzyme M knock-out mice reveal little or no deficit in their cytotoxic lymphocytes’ killing ability ex vivo, but indicate impairment in the inflammatory response. These findings of non-cytotoxic effects of granzymes challenge dogma, and thus require alternative or additional explanations to be developed of the role of granzymes in defeating pathogens. Here we review evidence for granzyme cytotoxicity, give an overview of their non-cytotoxic functions, and suggest technical improvements for future investigations.

Inflammasomes in the CNS

Microglia and macrophages in the CNS contain multimolecular complexes termed inflammasomes. Inflammasomes function as intracellular sensors for infectious agents as well as for host-derived danger signals that are associated with neurological diseases, including meningitis, stroke and Alzheimer's disease. Assembly of an inflammasome activates caspase 1 and, subsequently, the proteolysis and release of the cytokines interleukin-1β and interleukin-18, as well as pyroptotic cell death. Since the discovery of inflammasomes in 2002, there has been burgeoning recognition of their complexities and functions. Here, we review the current understanding of the functions of different inflammasomes in the CNS and their roles in neurological diseases.

Calpains promote neutrophil recruitment and bacterial clearance in an acute bacterial peritonitis model

Activation of the innate immune system is critical for clearance of bacterial pathogens to limit systemic infections and host tissue damage. Here, we report a key role for calpain proteases in bacterial clearance in mice with acute peritonitis. Using transgenic mice expressing Cre recombinase primarily in innate immune cells (fes-Cre), we generated conditional capns1 knockout mice. Consistent with capns1 being essential for stability and function of the ubiquitous calpains (calpain-1, calpain-2), peritoneal cells from these mice had reduced levels of calpain-2/capns1, and reduced proteolysis of their substrate selenoprotein K. Using an acute bacterial peritonitis model, we observed impaired bacterial killing within the peritoneum and development of bacteremia in calpain knockout mice. These defects correlated with significant reductions in IL-1α release, neutrophil recruitment, and generation of reactive oxygen species in calpain knockout mice with acute bacterial peritonitis. Peritoneal macrophages from calpain knockout mice infected with enterobacteria ex vivo, were competent in phagocytosis of bacteria, but showed impaired clearance of intracellular bacteria compared with control macrophages. Together, these results implicate calpains as key mediators of effective innate immune responses to acute bacterial infections, to prevent systemic dissemination of bacteria that can lead to sepsis.

Natural killer cell NKG2D and granzyme B are critical for allergic pulmonary inflammation

BACKGROUND

The diverse roles of innate immune cells in the pathogenesis of asthma remain to be fully defined. Natural killer (NK) cells are innate lymphocytes that can regulate adaptive immune responses. NK cells are activated in asthma; however, their role in allergic airway inflammation is not fully understood.

OBJECTIVE

We investigated the importance of NK cells in house dust mite (HDM)-triggered allergic pulmonary inflammation. Specifically, we aimed to determine the role of the major NK-cell activating receptor NKG2D and NK-cell effector functions mediated by granzyme B.

METHODS

Allergic airway inflammation was induced in the airways of mice by repeated intranasal HDM extract administration and responses in wild-type and NKG2D-deficient mice were compared. Adoptive transfer studies were used to identify the cells and mechanisms involved.

RESULTS

Mice that lacked NKG2D were resistant to the induction of allergic inflammation and showed little pulmonary eosinophilia, few airway TH2 cells, and no rise in serum IgE after multiple HDM-allergen exposures. However, NKG2D was not required for pulmonary inflammation after a single inoculation of allergen. NKG2D-deficient mice showed no alteration in responses to respiratory virus infection. Transfer of wild-type NK cells (but not CD3(+) cells) into NKG2D-deficient mice restored allergic inflammatory responses only if the NK cells expressed granzyme B.

CONCLUSIONS

These studies established a pivotal role for NK-cell NKG2D and granzyme B in the pathogenesis of HDM-induced allergic lung disease, and identified novel therapeutic targets for the prevention and treatment of asthma.

Plasma granzyme B in ST elevation myocardial infarction versus non-ST elevation acute coronary syndrome: comparisons with IL-18 and fractalkine

OBJECTIVE

The proapoptotic protein, granzyme B (GZB), was identified as a contributor to the atherosclerotic plaque instability and recently as inflammatory activator. We studied the release kinetics of GZB and other markers of inflammation such as high sensitivity C reactive protein (hsCRP), interleukin 18 (IL-18), and fractalkine (FKN) in the early phase after acute cardiac events in different ACS subgroups.

METHODS

Thirty-six nondiabetic patients with ACS were compared to 12 control subjects. According to ACS diagnosis, the patients were classified into 22 patients with ST elevation myocardial infarction (STEMI) and 14 patients with non-ST elevation myocardial infarction or unstable angina (NSTEMI/UA). Blood samples were taken on day 1 (day of onset) and day 3 to measure hsCRP, IL-18, FKN, and GZB by ELISA.

RESULTS

Patients with ACS showed significantly higher GZB, IL-18, and FKN levels than the controls. STEMI group showed significantly higher GZB levels than NSTEMI/UA group. On day 3, FKN levels displayed a significant decrease, while GZB levels were significantly increased. IL-18 levels were more or less constant. GZB levels were positively correlated with IL-18 (r = 0.416, P < 0.01) and FKN (r = 0.58, P < 0.001).

CONCLUSIONS

Unlike IL-18 and FKN, plasma GZB may be a marker of ACS disease severity.

The serine protease granzyme B as an inflammatory marker, in relation to the insulin receptor cleavage in human obesity and type 2 diabetes mellitus

Chronic inflammation and insulin resistance form hallmarks of type 2 diabetes mellitus (T2DM). An increased circulating level of the serine protease granzyme B (GzmB) is observed during prolonged inflammation and is implicated in the pathogenesis of several chronic inflammatory diseases. Moreover, insulin receptor cleavage by unknown proteases, yielding elevated levels of insulin receptor α-subunit (IRα), was observed in T2DM and was proposed as a new mechanism of insulin resistance. Therefore, a possible association between GzmB and IRα is suggested. Accordingly, this study was set to explore whether GzmB and IRα levels are altered in T2DM patients with the impact of obesity. Furthermore, we aimed to identify if GzmB contributes towards inflammation and insulin resistance through its suggested extracellular activities. All subjects were assessed for anthropometric and metabolic parameters related to obesity and T2DM. In addition, fasting plasma insulin, GzmB, interleukin-1β (IL-1β), and IRα levels were estimated by enzyme linked immunosorbent assay. Levels of GzmB and IRα were found to be significantly elevated in T2DM patients compared to nondiabetic subjects. In addition, GzmB levels were positively correlated with measures of obesity and insulin resistance, IL-1β, IRα, and other metabolic parameters. While multiple linear regression analysis revealed that both T2DM and central obesity were predicting factors for GzmB, our findings reveal a possible role of GzmB in T2DM.