Gene-Dose Effect of MEFV Gain-of-Function Mutations Determines ex vivo Neutrophil Activation in Familial Mediterranean Fever

A narrative review on the role of cytokines in the pathogenesis and treatment of familial Mediterranean fever: an emphasis on pediatric cases

Familial Mediterranean Fever (FMF) is a hereditary autoinflammatory disease characterized by an early onset of recurrent fever and serositis episodes. FMF is caused by mutations in the MEFV gene which encodes the pyrin protein, an IL-1β mediated inflammation regulator. Recent findings have identified a plethora of molecules and pathways involved in the regulation of inflammation and innate immunity, hence increasing our understanding of the etiology and inflammatory nature of FMF. Cytokines, in particular, have been found to play a key role in the pathogenesis and treatment of the disease. Indeed, various studies associated cytokines' genetic variations and expression with susceptibility to and severity of the disease, which was further supported by the positive response of patients, both children and adults, to targeted cytokine blocking therapies. These studies highlighted the potential use of cytokines as biomarkers and target in resistant/intolerant patients and contributed to improving the early detection of FMF in children, thus enhancing their quality of life and providing alternative treatment for severe cases. The aim of this review is to provide the latest updates on the pivotal role of cytokines in FMF and to discuss the efficacy and safety of anti-cytokine biologics by primarily focusing on pediatric FMF cases.

Unmasking the NLRP3 inflammasome in dendritic cells as a potential therapeutic target for autoimmunity, cancer, and infectious conditions

Proper and functional immune response requires a complex interaction between innate and adaptive immune cells, which dendritic cells (DCs) are the primary actors in this coordination as professional antigen-presenting cells. DCs are armed with numerous pattern recognition receptors (PRRs) such as nucleotide-binding and oligomerization domain-like receptors (NLRs) like NLRP3, which influence the development of their activation state upon sensation of ligands. NLRP3 is a crucial component of the immune system for protection against tumors and infectious agents, because its activation leads to the assembly of inflammasomes that cause the formation of active caspase-1 and stimulate the maturation and release of proinflammatory cytokines. But, when NLRP3 becomes overactivated, it plays a pathogenic role in the progression of several autoimmune disorders. So, NLRP3 activation is strictly regulated by diverse signaling pathways that are mentioned in detail in this review. Furthermore, the role of NLRP3 in all of the diverse immune cells' subsets is briefly mentioned in this study because NLRP3 plays a pivotal role in modulating other immune cells which are accompanied by DCs' responses and subsequently influence differentiation of T cells to diverse T helper subsets and even impact on cytotoxic CD8+ T cells' responses. This review sheds light on the functional and therapeutic role of NLRP3 in DCs and its contribution to the occurrence and progression of autoimmune disorders, prevention of diverse tumors' development, and recognition and annihilation of various infectious agents. Furthermore, we highlight NLRP3 targeting potential for improving DC-based immunotherapeutic approaches, to be used for the benefit of patients suffering from these disorders.

Generation of iPSCs from a Patient with the M694V Mutation in the MEFV Gene Associated with Familial Mediterranean Fever and Their Differentiation into Macrophages

Familial Mediterranean fever (FMF) is a systemic autoinflammatory disorder caused by inherited mutations in the MEFV (Mediterranean FeVer) gene, located on chromosome 16 (16p13.3) and encoding the pyrin protein. Despite the existing data on MEFV mutations, the exact mechanism of their effect on the development of the pathological processes leading to the spontaneous and recurrent autoinflammatory attacks observed in FMF, remains unclear. Induced pluripotent stem cells (iPSCs) are considered an important tool to study the molecular genetic mechanisms of various diseases due to their ability to differentiate into any cell type, including macrophages, which contribute to the development of FMF. In this study, we developed iPSCs from an Armenian patient with FMF carrying the M694V, p.(Met694Val) (c.2080A>G, rs61752717) pathogenic mutation in exon 10 of the MEFV gene. As a result of direct differentiation, macrophages expressing CD14 and CD45 surface markers were obtained. We found that the morphology of macrophages derived from iPSCs of a patient with the MEFV mutation significantly differed from that of macrophages derived from iPSCs of a healthy donor carrying the wild-type MEFV gene.

Epigenetic, transcriptional, and functional characterization of myeloid cells in familial Mediterranean fever

Familial Mediterranean fever (FMF) is a periodic fever syndrome caused by variation in MEFV. FMF is known for IL-1β dysregulation, but the innate immune landscape of this disease has not been comprehensively described. Therefore, we studied circulating inflammatory proteins, and the function of monocytes and (albeit less extensively) neutrophils in treated FMF patients in remission. We found that monocyte IL-1β and IL-6 production was enhanced upon stimulation, in concordance with alterations in the plasma inflammatory proteome. We did not observe changes in neutrophil functional assays. Subtle differences in chromatin accessibility and transcriptomics in our small patient cohort further argued for monocyte dysregulation. Together, these observations suggest that the MEFV-mutation-mediated primary immune dysregulation in monocytes leads to chronic inflammation that is subsequently associated with counterregulatory epigenetic/transcriptional changes reminiscent of tolerance. These data increase our understanding of the innate immune changes in FMF, aiding future management of chronic inflammation in these patients.

NLRP3 exacerbates EAE severity through ROS-dependent NET formation in the mouse brain

BACKGROUND

Neutrophil extracellular trap (NET) has been implicated in the pathology of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). However, the specific contributions of NLRP3, a NET-associated molecule, to EAE pathogenesis and its regulatory role in NET formation remain unknown.

METHODS

To investigate the detrimental effect of NETs supported by NLRP3 in MS pathogenesis, we induced EAE in WT and NLRP3 KO mice and monitored the disease severity. At the peak of the disease, NET formation was assessed by flow cytometry, immunoblotting, and immunofluorescence staining. To further identify the propensity of infiltrated neutrophils, NET-related chemokine receptors, degranulation, ROS production, and PAD4 expression levels were evaluated by flow cytometry. In some experiments, mice were injected with DNase-1 to eliminate the formed NETs.

RESULTS

Our data revealed that neutrophils significantly infiltrate the brain and spinal cord and form NETs during EAE pathogenesis. NLRP3 significantly elevates NET formation, primarily in the brain. NLRP3 also modulated the phenotypes of brain-infiltrated and circulating neutrophils, augmenting CXCR2 and CXCR4 expression, thereby potentially enhancing NET formation. NLRP3 facilitates NET formation in a ROS-dependent and PAD4-independent manner in brain-infiltrated neutrophils. Finally, NLRP3-supported NET formation exacerbates disease severity, triggering Th1 and Th17 cells recruitment.

CONCLUSIONS

Collectively, our findings suggest that NLRP3-supported NETs may be an etiological factor in EAE pathogenesis, primarily in the brain. This study provides evidence that targeting NLRP3 could be a potential therapeutic strategy for MS, specifically by attenuating NET formation.

Experimental models in Familial Mediterranean Fever (FMF): Insights into pathophysiology and therapeutic strategies

Familial Mediterranean Fever (FMF) is a recurrent polyserositis characterized by self-limiting episodes or attacks of fever along with serosal inflammation. It mainly impacts people of the Mediterranean and Middle Eastern basin. FMF is a recessive autoinflammatory condition caused by mutation in the MEFV gene located on chromosome 16p13. MEFV mutations lead to the activation of the pyrin inflammasome resulting in an uncontrolled release of IL-1β. Various in vitro, in vivo and ex vivo experimental models have been developed to further comprehend the etiology and pathogenesis of FMF. These models have been proven to be clinically relevant to human FMF and can provide significant information about biological systems with respect to this condition. Additionally, these models have provided pertinent contributions to the development of potent therapeutic strategies against FMF. In this review, we describe the different experimental models utilized in FMF and we focus primarily on the most widely used models that have produced prominent insights into the pathophysiology of the disease.

Biological and clinical roles of IL-18 in inflammatory diseases

Several new discoveries have revived interest in the pathogenic potential and possible clinical roles of IL-18. IL-18 is an IL-1 family cytokine with potent ability to induce IFNγ production. However, basic investigations and now clinical observations suggest a more complex picture. Unique aspects of IL-18 biology at the levels of transcription, activation, secretion, neutralization, receptor distribution and signalling help to explain its pleiotropic roles in mucosal and systemic inflammation. Blood biomarker studies reveal a cytokine for which profound elevation, associated with detectable 'free IL-18', defines a group of autoinflammatory diseases in which IL-18 dysregulation can be a primary driving feature, the so-called 'IL-18opathies'. This impressive specificity might accelerate diagnoses and identify patients amenable to therapeutic IL-18 blockade. Pathogenically, human and animal studies identify a preferential activation of CD8+ T cells over other IL-18-responsive lymphocytes. IL-18 agonist treatments that leverage the site of production or subversion of endogenous IL-18 inhibition show promise in augmenting immune responses to cancer. Thus, the unique aspects of IL-18 biology are finally beginning to have clinical impact in precision diagnostics, disease monitoring and targeted treatment of inflammatory and malignant diseases.

Fast and furious: The neutrophil and its armamentarium in health and disease

Neutrophils are powerful effector cells leading the first wave of acute host-protective responses. These innate leukocytes are endowed with oxidative and nonoxidative defence mechanisms, and play well-established roles in fighting invading pathogens. With microbicidal weaponry largely devoid of specificity and an all-too-well recognized toxicity potential, collateral damage may occur in neutrophil-rich diseases. However, emerging evidence suggests that neutrophils are more versatile, heterogeneous, and sophisticated cells than initially thought. At the crossroads of innate and adaptive immunity, neutrophils demonstrate their multifaceted functions in infectious and noninfectious pathologies including cancer, autoinflammation, and autoimmune diseases. Here, we discuss the kinetics of neutrophils and their products of activation from bench to bedside during health and disease, and provide an overview of the versatile functions of neutrophils as key modulators of immune responses and physiological processes. We focus specifically on those activities and concepts that have been validated with primary human cells.

The NLRP3 inflammasome: contributions to inflammation-related diseases

The NOD-like receptor protein 3 (NLRP3) inflammasome is a protein complex that regulates innate immune responses by activating caspase-1 and the inflammatory cytokines interleukin (IL)-1β and IL-18. Multiple studies have demonstrated the importance of the NLRP3 inflammasome in the development of immune and inflammation-related diseases, including arthritis, Alzheimer's disease, inflammatory bowel disease, and other autoimmune and autoinflammatory diseases. This review first explains the activation and regulatory mechanism of the NLRP3 inflammasome. Secondly, we focus on the role of the NLRP3 inflammasome in various inflammation-related diseases. Finally, we look forward to new methods for targeting the NLRP3 inflammasome to treat inflammation-related diseases, and provide new ideas for clinical treatment.

Juvenile-onset systemic lupus erythematosus and MEFV polymorphism: A case-control association study among Iranian children

INTRODUCTION AND OBJECTIVES

This study is designed to evaluate the potential influences of Mediterranean fever gene (MEFV) gene polymorphism on systemic lupus erythematosus (SLE) in a cohort of juvenile patients. A case-control study was performed on Iranian patients with a mixed ethnicity population.

PATIENTS AND METHODS

Genotypes of 50 juvenile cases, and 85 healthy controls were investigated for identifying M694V and R202Q polymorphism. Genotyping was done utilizing amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) to detect M694V and R202Q mutations, respectively.

MAIN FINDINGS

Our study indicates significant differences in the alleles and genotypes frequencies of MEFV polymorphism between SLE patients and healthy controls (P<0.05). Also, an association was found between renal involvement (50% vs. 8.3%, P=0.000, OR=0.91, 95% CI=0.30-0.278) in juvenile SLE patients and M694V polymorphism incident; But there was no association with other clinical manifestations.

PRINCIPAL CONCLUSION

We found a significant association between R202Q and M694V polymorphism of the MEFV gene and susceptibility to SLE in the studied population; However, further studies on detailed characterization of these polymorphisms' impacts on the key elements responsible for SLE pathogenesis is of great importance.

NLRP3 Exacerbate NETosis-Associated Neuroinflammation in an LPS-Induced Inflamed Brain

Neutrophil extracellular traps (NETs) exert a novel function of trapping pathogens. Released NETs can accumulate in inflamed tissues, be recognized by other immune cells for clearance, and lead to tissue toxicity. Therefore, the deleterious effect of NET is an etiological factor, causing several diseases directly or indirectly. NLR family pyrin domain containing 3 (NLRP3) in neutrophils is pivotal in signaling the innate immune response and is associated with several NET-related diseases. Despite these observations, the role of NLRP3 in NET formation in neuroinflammation remains elusive. Therefore, we aimed to explore NET formation promoted by NLRP3 in an LPS-induced inflamed brain. Wild-type and NLRP3 knockout mice were used to investigate the role of NLRP3 in NET formation. Brain inflammation was systemically induced by administering LPS. In such an environment, the NET formation was evaluated based on the expression of its characteristic indicators. DNA leakage and NET formation were analyzed in both mice through Western blot, flow cytometry, and in vitro live cell imaging as well as two-photon imaging. Our data revealed that NLRP3 promotes DNA leakage and facilitates NET formation accompanied by neutrophil death. Moreover, NLRP3 is not involved in neutrophil infiltration but is predisposed to boost NET formation, which is accompanied by neutrophil death in the LPS-induced inflamed brain. Furthermore, either NLRP3 deficiency or neutrophil depletion diminished pro-inflammatory cytokine, IL-1β, and alleviated blood-brain barrier damage. Overall, the results suggest that NLRP3 exacerbates NETosis in vitro and in the inflamed brain, aggravating neuroinflammation. These findings provide a clue that NLRP3 would be a potential therapeutic target to alleviate neuroinflammation.

A Well-Intentioned Enemy in Autoimmune and Autoinflammatory Diseases: NETosis

Neutrophils are an essential member of the innate immune system derived from the myeloid stem cell series and develop in the bone marrow. The action of neutrophils defined in immune response includes phagocytosis, degranulation, cytokine production, and neutrophil extracellular traps. The success of the host immune defense depends on effective neutrophil activation. Recent studies have shown that neutrophils that have completed their task in the field of inflammation rejoin circulation. Uncontrolled inflammatory response and dysregulated immune responses to the host are important factors in the development of acute and chronic diseases. Neutrophils are the first cells to be drawn into the field at the time of inflammation. They have developed response strategies that produce proinflammatory cytokines and are known as neutrophil extracellular traps since they create mesh-like structures with their DNA contents into the external environment and release their granular proteins in this way. This article summarizes numerous recent studies and reviews the role of neutrophil extracellular traps in autoimmune and autoinflammatory diseases in the hope, that this will lead to the development of more effective treatments. In addition, in this review, the role of neutrophil extracellular trap formation in some pediatric autoimmune diseases is emphasized.

Identification of a Germline Pyrin Variant in a Metastatic Melanoma Patient With Multiple Spontaneous Regressions and Immune-related Adverse Events

The mechanisms underlying tumor immunosurveillance and their association with the immune-related adverse events (irAEs) associated with checkpoint inhibitor immunotherapies remain poorly understood. We describe a metastatic melanoma patient exhibiting multiple episodes of spontaneous disease regression followed by the development of several irAEs during the course of anti-programmed cell death protein 1 antibody immunotherapy. Whole-exome next-generation sequencing studies revealed this patient to harbor a pyrin inflammasome variant previously described to be associated with an atypical presentation of familial Mediterranean fever. This work highlights a potential role for inflammasomes in the regulation of tumor immunosurveillance and the pathogenesis of irAEs.

Pericarditis and Autoinflammation: A Clinical and Genetic Analysis of Patients With Idiopathic Recurrent Pericarditis and Monogenic Autoinflammatory Diseases at a National Referral Center

Background Idiopathic recurrent pericarditis (IRP) is an orphan disease that carries significant morbidity, partly driven by corticosteroid dependence. Innate immune modulators, colchicine and anti-interleukin-1 agents, pioneered in monogenic autoinflammatory diseases, have demonstrated remarkable efficacy in trials, suggesting that autoinflammation may contribute to IRP. This study characterizes the phenotype of patients with IRP and monogenic autoinflammatory diseases, and establishes whether autoinflammatory disease genes are associated with IRP. Methods and Results We retrospectively analyzed the medical records of patients with IRP (n=136) and monogenic autoinflammatory diseases (n=1910) attending a national center (London, UK) between 2000 and 2021. We examined 4 genes (MEFV, MVK, NLRP3, TNFRSF1A) by next-generation sequencing in 128 patients with IRP and compared the frequency of rare deleterious variants to controls obtained from the Genome Aggregation Database. In this cohort of patients with IRP, corticosteroid dependence was common (39/136, 28.7%) and was associated with chronic pain (adjusted odds ratio 2.8 [95% CI, 1.3-6.5], P=0.012). IRP frequently manifested with systemic inflammation (raised C-reactive protein [121/136, 89.0%] and extrapericardial effusions [68/136, 50.0%]). Pericarditis was observed in all examined monogenic autoinflammatory diseases (0.4%-3.7% of cases). Rare deleterious MEFV variants were more frequent in IRP than in ancestry-matched controls (allele frequency 9/200 versus 2932/129 200, P=0.040). Conclusions Pericarditis is a feature of interleukin-1 driven monogenic autoinflammatory diseases and IRP is associated with variants in MEFV, a gene involved in interleukin-1β processing. We also found that corticosteroid dependence in IRP is associated with chronic noninflammatory pain. Together these data implicate autoinflammation in IRP and support reducing reliance on corticosteroids in its management.

Assessment of Surrogate Markers for Cardiovascular Disease in Familial Mediterranean Fever-Related Amyloidosis Patients Homozygous for M694V Mutation in MEFV Gene

Cardiovascular disease (CVD) remains underestimated in familial Mediterranean fever-associated AA amyloidosis (FMF-AA). We aimed to compare early markers of endothelial dysfunction and atherosclerosis in FMF-AA with a homozygous M694V mutation (Group 1 = 76 patients) in the Mediterranean fever (MEFV) gene and in patients with other genotypes (Group 2 = 93 patients). Measures of increased risk for future CVD events and endothelial dysfunction, including flow-mediated dilatation (FMD), pentraxin-3 (PTX3), and carotid intima-media thickness (cIMT), and fibroblast growth factor 23 (FGF23) as a marker of atherosclerotic vascular disease were compared between groups. The frequency of clinical FMF manifestations did not differ between the two groups apart from arthritis (76.3% in Group 1 and 59.1% in Group 2, p < 0.05). FMD was significantly lower in Group 1 when compared with Group 2 (MD [95% CI]: −0.6 [(−0.89)−(−0.31)]). cIMT, FGF23, and PTX3 levels were higher in Group 1 (cIMT MD [95% CI]: 0.12 [0.08−0.16]; FGF23 MD [95% CI]: 12.8 [5.9−19.6]; PTX3 MD [95% CI]: 13.3 [8.9−17.5]). In patients with FMF-AA, M694V homozygosity is associated with lower FMD values and higher cIMT, FGF23, and PTX3 levels, suggesting increased CVD risk profiles. These data suggest that a genotype−phenotype association exists in terms of endothelial dysfunction and atherosclerosis in patients with FMF-AA.

Excess Serum Interleukin-18 Distinguishes Patients With Pathogenic Mutations in PSTPIP1

OBJECTIVE

Dominantly inherited PSTPIP1 mutations cause a spectrum of autoinflammatory manifestations epitomized by PAPA syndrome (pyogenic sterile arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome.). The connections between PSTPIP1 and PAPA syndrome are poorly understood, although evidence suggests involvement of pyrin inflammasome activation. Interleukin-18 (IL-18) is an inflammasome-activated cytokine associated with susceptibility to macrophage activation syndrome (MAS). This study was undertaken to investigate an association of IL-18 with PAPA syndrome.

METHODS

Clinical and genetic data and serum samples were obtained from patients referred to institutions due to symptoms indicative of PAPA syndrome. Serum IL-18, IL-18 binding protein (IL-18BP), and CXCL9 levels were assessed by bead-based assay, and free IL-18 levels were assessed by enzyme-linked immunosorbent assay.

RESULTS

The symptoms of PSTPIP1-positive patients with PAPA syndrome overlapped with those of mutation-negative patients with PAPA-like conditions, but mutation-positive patients had earlier onset and a greater proportion had a history of arthritis. We found uniform elevation of total serum IL-18 in treated PAPA syndrome patients at levels nearly as high as those seen in NLRC4-associated autoinflammation with infantile enterocolitis patients, and well above levels found in most familial Mediterranean fever patients. Serum IL-18 elevation in PAPA syndrome patients persisted despite fluctuations in disease activity. Levels of the soluble IL-18 antagonist IL-18BP were modestly elevated, and PAPA syndrome patients had detectable free IL-18. PAPA syndrome was rarely associated with elevation of CXCL9, an indicator of interferon-γ activity, but no PAPA syndrome patients had a history of MAS.

CONCLUSION

PAPA syndrome is a refractory and often disabling monogenic autoinflammatory disease associated with chronic and unopposed elevation of serum IL-18 levels but not with risk of MAS. These findings affect our understanding of the diseases in which IL-18 is overproduced and suggest a link between pyrin inflammasome activation, IL-18, and autoinflammation, without susceptibility to MAS.

Evaluation of S100A12 protein levels in children with familial Mediterranean fever

Background/aim

Familial Mediterranean fever (FMF), the most common autoinflammatory disease in children, is characterized by recurrent febrile episodes. FMF is known to progress with chronic inflammation, particularly during attack periods. This study aimed to investigate the relationship of S100A12, an inflammatory marker, with attacks and inflammatory events in FMF patients.

Materials and methods

The study included 57 patients diagnosed with FMF, 43 in an attack-free period and 14 in an attack period, and 31 healthy children as the control group. Only white blood cell (WBC) count, C-reactive protein (CRP) level, erythrocyte sedimentation rate (ESR), and S100A12 level were analyzed in the control group. In addition, serum amyloid A (SAA), and fibrinogen levels were measured, and a mutation analysis was performed in the patient group. The results were compared among the attack-free period, acute attack FMF and control groups.

Results

The mean age of patients and control group was 10 (2.5–18) and 9.5 (2.5–16) years, respectively. The CRP (p = 0.001), S100A12 (p = 0.003) and ESR (p= 0.001) values differed significantly between the FMF and control groups. S100A12 level (p = 0.027), WBC count (p = 0.003), CRP level (p = 0.0001), ESR (p = 0.004), and fibrinogen level (p = 0.001) differed significantly between the acute attack and attack-free period groups. SAA level (p = 0.05), ESR (p = 0.001), fibrinogen level (p = 0.001), WBC count (p = 0.001), and S100A12 level (p = 0.027) were higher in M694V homozygous FMF patients than in other FMF patients.

Conclusion

Patients with FMF had higher S100A12 levels than the control group, while the mean S100A12 concentration was higher in acute attack period patients than in attack-free period patients. S100A12 level might be an important indicator in the monitoring of chronic inflammation in patients with FMF.

NLRP3 Inflammasome Assembly in Neutrophils Is Supported by PAD4 and Promotes NETosis Under Sterile Conditions

Neutrophil extracellular trap formation (NETosis) and the NLR family pyrin domain containing 3 (NLRP3) inflammasome assembly are associated with a similar spectrum of human disorders. While NETosis is known to be regulated by peptidylarginine deiminase 4 (PAD4), the role of the NLRP3 inflammasome in NETosis was not addressed. Here, we establish that under sterile conditions the cannonical NLRP3 inflammasome participates in NETosis. We show apoptosis-associated speck-like protein containing a CARD (ASC) speck assembly and caspase-1 cleavage in stimulated mouse neutrophils without LPS priming. PAD4 was needed for optimal NLRP3 inflammasome assembly by regulating NLRP3 and ASC protein levels post-transcriptionally. Genetic ablation of NLRP3 signaling resulted in impaired NET formation, because NLRP3 supported both nuclear envelope and plasma membrane rupture. Pharmacological inhibition of NLRP3 in either mouse or human neutrophils also diminished NETosis. Finally, NLRP3 deficiency resulted in a lower density of NETs in thrombi produced by a stenosis-induced mouse model of deep vein thrombosis. Altogether, our results indicate a PAD4-dependent formation of the NLRP3 inflammasome in neutrophils and implicate NLRP3 in NETosis under noninfectious conditions in vitro and in vivo.

Molecular mechanisms of phenotypic variability in monogenic autoinflammatory diseases

Monogenic autoinflammatory diseases are a group of rheumatologic disorders caused by dysregulation in the innate immune system. The molecular mechanisms of these disorders are linked to defects in inflammasome-mediated, NF-κB-mediated or interferon-mediated inflammatory signalling pathways, cytokine receptors, the actin cytoskeleton, proteasome complexes and various enzymes. As with other human disorders, disease-causing variants in a single gene can present with variable expressivity and incomplete penetrance. In some cases, pathogenic variants in the same gene can be inherited either in a recessive or dominant manner and can cause distinct and seemingly unrelated phenotypes, although they have a unifying biochemical mechanism. With an enhanced understanding of protein structure and functionality of protein domains, genotype-phenotype correlations are beginning to be unravelled. Many of the mutated proteins are primarily expressed in haematopoietic cells, and their malfunction leads to systemic inflammation. Disease presentation is also defined by a specific effect of the mutant protein in a particular cell type and, therefore, the resulting phenotype might be more deleterious in one tissue than in another. Many patients present with the expanded immunological disease continuum that includes autoinflammation, immunodeficiency, autoimmunity and atopy, which necessitate genetic testing.

Transmigration of Neutrophils From Patients With Familial Mediterranean Fever Causes Increased Cell Activation

Familial Mediterranean fever (FMF) is caused by pyrin-encoding MEFV gene mutations and characterized by the self-limiting periods of intense inflammation, which are mainly mediated by a massive influx of polymorphonuclear neutrophils (PMNs) into the inflamed sites. Perturbation of actin polymerization by different pathogens was shown to activate the pyrin inflammasome. Our aim was to test whether cytoskeletal dynamics in the absence of pathogens may cause abnormal activation of PMNs from FMF patients. We also aimed to characterize immunophenotypes of circulating neutrophils and their functional activity. Circulating PMNs displayed heterogeneity in terms of cell size, granularity and immunophenotypes. Particularly, PMNs from the patients in acute flares (FMF-A) exhibited a characteristic of aged/activated cells (small cell size and granularity, up-regulated CXCR4), while PMNs form the patients in remission period (FMF-R) displayed mixed fresh/aged cell characteristics (normal cell size and granularity, up-regulated CD11b, CD49d, CXCR4, and CD62L). The findings may suggest that sterile tissue-infiltrated PMNs undergo reverse migration back to bone marrow and may explain why these PMNs do not cause immune-mediated tissue damage. A multidirectional expression of FcγRs on neutrophils during acute flares was also noteworthy: up-regulation of FcγRI and down-regulation of FcγRII/FcγRIII. We also observed spontaneous and fMPL-induced activation of PMNs from the patients after transmigration through inserts as seen by the increased expression of CD11b and intracellular expression of IL-1β. Our study suggests heightened sensitivity of mutated pyrin inflammasome towards cytoskeletal modifications in the absence of pathogens.

Phenotypical and Functional Characterization of Neutrophils in Two Pyrin-Associated Auto-inflammatory Diseases

PURPOSE

Familial Mediterranean Fever (FMF) and Pyrin-Associated Autoinflammation with Neutrophilic Dermatosis (PAAND) are clinically distinct autoinflammatory disorders caused by mutations in the pyrin-encoding gene MEFV. We investigated the transcriptional, phenotypical, and functional characteristics of patient neutrophils to explore their potential role in FMF and PAAND pathophysiology.

METHODS

RNA sequencing was performed to discover transcriptional aberrancies. The phenotypical features, degranulation properties, and phagocytic capacity of neutrophils were assessed by flow cytometry. Production of reactive oxygen species (ROS), myeloperoxidase (MPO) release, and chemotactic responses were investigated via chemiluminescence, ELISA, and Boyden chamber assays, respectively.

RESULTS

Neutrophils from PAAND and FMF patients showed a partially overlapping, activated gene expression profile with increased expression of S100A8, S100A9, S100A12, IL-4R, CD48, F5, MMP9, and NFKB. Increased MMP9 and S100A8/A9 expression levels were accompanied by high plasma concentrations of the encoded proteins. Phenotypical analysis revealed that neutrophils from FMF patients exhibited an immature character with downregulation of chemoattractant receptors CXCR2, C5aR, and BLTR1 and increased expression of Toll-like receptor 4 (TLR4) and TLR9. PAAND neutrophils displayed an increased random, but reduced CXCL8-induced migration. A tendency for enhanced random migration was observed for FMF neutrophils. PAAND neutrophils showed a moderately but significantly enhanced phagocytic activity as opposed to neutrophils from FMF patients. Neutrophils from both patient groups showed increased MPO release and ROS production.

CONCLUSIONS

Neutrophils from patients with FMF and PAAND, carrying different mutations in the MEFV gene, share a pro-inflammatory phenotype yet demonstrate diverse features, underscoring the distinction between both diseases.

TRIM Proteins in Inflammation: from Expression to Emerging Regulatory Mechanisms

Inflammation is an immune response to exogenous or endogenous insults that helps to maintain the tissue homeostasis under stressful conditions. Depending on the differential types of insults, inflammation is classified into microbial, autoimmune, metabolic, allergic, and physical inflammation. With regard to its involvement in the pathogenesis of most of human diseases, dissecting the key molecules in the regulation of inflammatory process is vital for the prevention and therapeutics of human diseases. Tripartite motif (TRIM) proteins are a versatile family of E3 ligases, which are composed of > 80 distinct members in humans recognized for their roles in antiviral responses. Recently, a large number of studies have shown the regulatory roles of TRIM proteins in mediating the inflammation. Herein in this review, we discuss the aberrations of TRIM proteins in autoimmune and autoinflammatory diseases, with a focus on the regulation of different components of inflammatory process, including inflammasome, NF-κB signaling, type I IFN (interferon) production, and Th1/Th17 cell differentiation. Importantly, elucidation of the mechanism underlying the regulation of inflammation by TRIMs provides insights into the use of TRIMs as therapeutic targets for disease treatment.