Adjunctive silymarin supplementation and its effects on disease severity, oxidative stress, and inflammation in patients with Alzheimer's disease.

BACKGROUND: Brain tissue in Alzheimer's patients is exposed to oxidative stress. Silymarin is an adjunct drug that has anti-inflammatory and antioxidant properties. OBJECTIVE: This study aimed to evaluate the effect of silymarin on biomarkers of oxidative stress, inflammation, and disease severity in Alzheimer's patients. METHODS: This randomized, single-blind clinical trial study was performed on 33 patients with Alzheimer's disease (AD) whose disease was confirmed by DSM-5 criteria and by brain imaging. Patients in the case group received three 250 mg silymarin capsules daily (each containing 150 mg silymarin), as an adjunctive medication in addition to the routine medication regimen. In the placebo group (control), patients received the same amount of placebo. All patients underwent Mini Mental State Exam (MMSE) and a panel of blood tests including malondialdehyde, neopterin, catalase, paraoxonase-1, total oxidative status, and total antioxidant capacity to reevaluate the changes pre/postintervention at the end of the trimester. RESULTS: The catalase and MDA serum levels after the adjunctive silymarin treatment decreased significantly (Catalasebefore silymarin = 9.29 ± 7.02 vs Catalaseafter silymarin = 5.32 ± 2.97, p = 0.007 and MDAbefore silymarin = 4.29 ± 1.90 vs MDAafter silymarin = 1.66 ± 0.84, p < 0.001) while MMSE increased notably (MMSEbefore silymarin = 10.39 ± 6.42 vs MMSEafter silymarin = 13.37 ± 6.81, p < 0.001). CONCLUSION: Silymarin can be effective as an adjunct drug and a powerful antioxidant in reducing oxidative stress and improving the course of AD.

Association of angiotensin-converting enzyme (ACE) I/D variation with biochemical parameters and oxidative stress markers in systemic lupus erythematosus patients in west of Iran.

PURPOSE: We aimed to study insertion/deletion (I/D) variation (rs4646994) of ACE gene in a group of SLE patients in west of Iran and its possible relationship with oxidative stress. METHOD AND RESULTS: Genotypes and allele frequencies related to ACE (I/D) variation were determined in 108 SLE patients and 110 gender and age-matched healthy controls using PCR. Neopterin, malondialdehyde (MDA), and serum lipid concentrations were determined by HPLC and enzyme assay respectively. The overall distribution of ACE I/D genotypes in SLE patients was different from that of the control group (P = 0.005). DD genotype compared to ID genotype increased the risk of SLE (OR = 2.57, 95% CI 1.4-4.8, P = 0.003). ID genotype compared to the II genotype decreased the risk of disease (OR = 0.45, 95% CI 0.2-0.99, p = 0.042). SLE patients with DD, ID, and II genotypes had lower paraoxonase (PON) activity and higher serum levels of MDA and neopterin versus control patients. We also detected a significant protective effect against SLE in presence of ACE I alleles and lack of angiotensin II receptor, type 1 (AGTR1) A1166C (NCBI reference SNP id: rs5186), C alleles in this study (OR = 0.31, 95% CI 0.14-0.68, P = 0.002). CONCLUSIONS: Carriers of the DD genotype of ACE gene with higher serum concentrations of neopterin and MDA, and lower PON activity had a high risk to develop SLE, while ID genotype decreased the risk of disease development by 2.22 times compared to II genotype.

Space-Flight- and Microgravity-Dependent Alteration of Mast Cell Population and Protease Expression in Digestive Organs of Mongolian Gerbils.

Mast cell (MC)-specific proteases are of particular interest for space biology and medicine due to their biological activity in regulating targets of a specific tissue microenvironment. MC tryptase and chymase obtain the ability to remodel connective tissue through direct and indirect mechanisms. Yet, MC-specific protease expression under space flight conditions has not been adequately investigated. Using immunohistochemical stainings, we analyzed in this study the protease profile of the jejunal, gastric, and hepatic MC populations in three groups of Mongolian gerbils-vivarium control, synchronous experiment, and 12-day orbital flight on the Foton-M3 spacecraft-and in two groups-vivarium control and anti-orthostatic suspension-included in the experiment simulating effects of weightlessness in the ground-based conditions. After a space flight, there was a decreased number of MCs in the studied organs combined with an increased proportion of chymase-positive MCs and MCs with a simultaneous content of tryptase and chymase; the secretion of specific proteases into the extracellular matrix increased. These changes in the expression of proteases were observed both in the mucosal and connective tissue MC subpopulations of the stomach and jejunum. Notably, the relative content of tryptase-positive MCs in the studied organs of the digestive system decreased. Space flight conditions simulated in the synchronous experiment caused no similar significant changes in the protease profile of MC populations. The space flight conditions resulted in an increased chymase expression combined with a decreased total number of protease-positive MCs, apparently due to participating in the processes of extracellular matrix remodeling and regulating the state of the cardiovascular system.

Chronic urticaria and the pathogenic role of mast cells.

The signs and symptoms of chronic urticaria (CU) are caused by the activation and degranulation of skin mast cells (MCs). Recent studies have added to our understanding of how and why skin MCs are involved and different in CU. Also, novel and relevant mechanisms of MC activation in CU have been identified and characterized. Finally, the use of MC-targeted and MC mediator-specific treatments has helped to better define the role of the skin environment, the contribution of specific MC mediators, and the relevance of MC crosstalk with other cells in the pathogenesis of CU. Here, we review these recent findings and their impact on our understanding of CU, with a focus on chronic spontaneous urticaria (CSU). Also, we highlight open questions, issues of controversy, and unmet needs, and we suggest what studies should be performed moving forward.

The role of caveolin-1 and endothelial nitric oxide synthase polymorphisms in susceptibility to prostate cancer.

Caveolin-1(cav-1) is overexpressed in prostate cancer (PC) and is associated with progression of the disease. We investigated the effects of CAV1-T29107A and endothelial nitric oxide synthase (eNOS) G894T polymorphisms on the serum levels of testosterone, NO and prostate-specific antigen (PSA) in patients with PC. We genotyped cav-1 and eNOS genes in 112 PC patients and 150 healthy controls by PCR-RFLP. Serum levels of NO2- and NO3- were measured using spectrophotometry, and serum levels of testosterone and PSA were measured by ELISA. The frequencies of CAV1 genotypes A/T vs. A/A according to the dominant model AT + TT vs. AA genotype and T allele were significantly higher in PC patients in comparison with the control group and considerably increased the risk of disease by 2.19-, 1.44- and 1.6-fold, respectively. AT + TT genotypes were associated significantly with the increased risk of PC in those with smoking or diabetes by 3.08-fold (P = .004). Individuals carrying concurrently the T allele of CAV1 A29107T and the T allele of eNOS G894T genes had a significantly increased risk of PC by 2.52-fold (P = .009). We did not find any significant relationship between eNOS G894T genotypes and alleles with susceptibility to PC. Our results highlighted the significance of CAV1-T29107A SNP but not (eNOS) G894T in the susceptibility to PC in our the population that we have studied.

Markers for the involvement of endothelial cells and the coagulation system in chronic urticaria: A systematic review.

Chronic urticaria (CU) is a chronic inflammatory mast cell-driven disorder. Endothelial cells (ECs) contribute importantly to key features of CU. Several markers of EC (dys)function in CU have been reported, but have not yet been systematically reviewed. In this study, we systematically reviewed and categorized all published markers of EC functions in CU through a comprehensive search in Pubmed, The Cochrane Library, Web of Science, and SCOPUS using the following Mesh terms: CU AND pathogenesis AND (vasculopathy OR microangiopathy OR ECs OR marker). In total, 79 articles were selected and the identified biomarkers were categorized according to EC (dys)function in CU. The most frequent and consistently reported upregulated biomarkers in CU skin were adhesion molecules, TF, and P-selectin. The most frequently reported upregulated and reliable biomarkers in sera of CU patients were F1+2 for coagulation cascade involvement, D-dimers for fibrinolysis, and MMP-9 for vascular permeability. Emerging biomarkers described in the selected articles were endostatin, heat shock proteins, cleaved high molecular weight kininogen, and adipokines. This systematic review contributes to the pool of growing evidence for vascular involvement in CU where EC dysfunction is present in different aspects of cell survival, maintenance of vascular structure, and coagulation/fibrinolysis balance.

Mast cells and complement system: Ancient interactions between components of innate immunity.

The emergence and evolution of the complement system and mast cells (MCs) can be traced back to sea urchins and the ascidian Styela plicata, respectively. Acting as a cascade of enzymatic reactions, complement is activated through the classical (CP), the alternative (AP), and the lectin pathway (LP) based on the recognized molecules. The system's main biological functions include lysis, opsonization, and recruitment of phagocytes. MCs, beyond their classic role as master cells of allergic reactions, play a role in other settings, as well. Thus, MCs are considered as extrahepatic producers of complement proteins. They express various complement receptors, including those for C3a and C5a. C3a and C5a not only activate the C3aR and C5aR expressing MCs but also act as chemoattractants for MCs derived from different anatomic sites, such as from the bone marrow, human umbilical cord blood, or skin in vitro. Cross talk between MCs and complement is facilitated by the production of complement proteins by MCs and their activation by the MC tryptase. The coordinated activity between MCs and the complement system plays a key role, for example, in a number of allergic, cutaneous, and vascular diseases. At a molecular level, MCs and complement system interactions are based on the production of several complement zymogens by MCs and their activation by MC-released proteases. Additionally, at a cellular level, MCs act as potent effector cells of complement activation by expressing receptors for C3a and C5a through which their chemoattraction and activation are mediated by anaphylatoxins in a paracrine and autocrine fashion.

Effects of temozolomide on U87MG glioblastoma cell expression of CXCR4, MMP2, MMP9, VEGF, anti-proliferatory cytotoxic and apoptotic properties.

Temozolomide is an alkylating agent which is used in glioblastoma treatment. We aimed to investigate the effects of different concentrations of temozolomide and exposure time on U87MG glioblastoma cell expression of CXCR4, MMP2, MMP9 and VEGF. U87MG cells were cultured in different temozolomide concentrations and incubation time and the effects of temozolomide on inducing apoptosis was investigated. The levels of VEGF and CXCR4 expression were measured by RT-PCR and flowcytometry. Moreover, MMP2 and MMP9 activity and expression were assessed by ELISA and zymography. CXCR4 and VEGF expression levels decreased upon applying higher concentration of temozolomide. MMP2 and MMP-9 had lower activity in cells with longer exposure time or higher doses of temozolomide. Temozolomide induces the apoptosis in U87MG glioblastoma cells at therapeutic or higher dose. It is capable of decreasing their expression levels of VEGF and CXCR4.

Association of AHSG gene polymorphisms with serum Fetuin-A levels in individuals with cardiovascular calcification in west of Iran.

Fetuin-A (AHSG) is a multifunctional secretory protein and acts as an ectopic valve and artery calcification inhibitor. We assessed the correlation between serum levels of Fetuin-A and both exon 6 (248 C/T) and exon 7 (256 C/G) mutations in patients with coronary artery calcification (CAC), mitral annular calcification (MAC), and aortic valve calcification (AVC). 184 patients and 184 healthy individuals as control group were included. The genetic variants of rs4917 and rs4918 for the AHSG gene were determined by PCR-RFLP and T-ARMS PCR techniques. Fetuin-A levels, fasting blood sugar (FBS), urea, creatinine, calcium phosphorus, and lipid profile were measured. Fetuin-A levels were remarkedly lower in individuals with AVC, MAC, and CAC comparing to the control group (p < 0.001). The CT + TT genotypes and the T allele (AHSG Thr248Met) were associated with the risk of calcification of heart valves and coronary artery by 1.31 and 1.27 times in the patient group, respectively. The frequency of CT genotype and T allele was considerably higher in the patient group comparing to the control group. Patients with T allele (CT + TT) had higher levels of FBS, urea, low-density lipoproteins (LDL)-C, phosphorus, systolic blood pressure (SBP), diastolic blood pressure (DBP) while decreased levels of triglyceride, high-density lipoproteins (HDL)-C, calcium and fetuin-A in comparison to control group. Additionally, there was a positive correlation between serum FBS, urea, creatinine, HDL-C, calcium with fetuin-A, and a negative correlation between phosphorous level, SBP, and DBP with fetuin-A. T allele in rs4917 Single nucleotide polymorphism (SNP) is the risk allele of calcification of heart valves and coronary arteries and fetuin-A levels correlates negatively with the occurrence of the disease.

The morphological basis of the development of the chick embryo immune system.

The chick immune system is a fundamental model in basic immunology. In birds, the bone marrow derived pluripotent stem cells after entering the circulation, migrate to bursa of Fabricius to benefit from a microenvironment which supports the differentiation and maturation of B lymphocytes by the help of its resident cells and tissues. Delivering sufficient functional B cells is required to maintain their peripheral population and normal peripheral humoral responses. Additionally, bursa acts as an active site for the generation of antibody diversity through gene conversion. Being consisted of 98% B lymphocytes, the organ is occupied by other cell types including T cells, macrophages, eosinophils and mast cells. Thymus, which is an epithelial organ is the main site of T cell development where positive and negative selections contribute to the development of functional and not autoreactive T cell repertoire. Bursectomy and thymectomy are surgical exercises through which the involvement of cells of specific immunity including B cells and T cells can be determined.

Investigation of Fc Receptor-Like 3 (FCRL-3) Gene Polymorphism (rs7528684) with Susceptibility to Allergic Asthma in Iranian North-Western Azeri Population.

BACKGROUND: Asthma is a clinical setting in which multiple cellular and molecular mechanisms are involved. Additionally, increasing genetic studies have provided evidence that single nucleotide polymorphisms (SNPs) in asthma relevant genes confer susceptibility to the disease. Fc receptor-like (FCRL) 3, a transmembrane molecule basically involved in B-cell signaling, mediates immune-disorders including allergy. Aim of study was to investigate the possible association of rs7528684 SNP in FCRL3 gene with a predisposition to allergic asthma in Iranian North-western Azeri population. METHODS: The frequency of genotypes and alleles of rs7528684 SNP in the FCRL3 gene was determined using the TaqMan genotyping method in 191 asthmatic patients and 186 healthy controls. RESULTS: The most frequent genotype in patients and control groups were CT (n = 81, 42.4%) and TT (n = 76, 40.9%), respectively. Statistical analysis showed no significant difference in genotype frequency (p = 0.81) and also in frequency of C and T alleles (p = 0.52) between two groups. CONCLUSIONS: Our results revealed no association between the rs7528684 SNP with susceptibility to allergic asthma in the included population. More studies in different ethnic groups will result in more valid conclusions.

Significance of extracellular vesicles in orchestration of immune responses in Mycobacterium tuberculosis infection.

Mycobacterium tuberculosis (M.tb), the causative agent of Tuberculosis, is an intracellular bacterium well known for its ability to subvert host energy and metabolic pathways to maintain its intracellular survival. For this purpose, the bacteria utilize various mechanisms of which extracellular vehicles (EVs) related mechanisms attracted more attention. EVs are nanosized particles that are released by almost all cell types containing active biomolecules from the cell of origin and can target bioactive pathways in the recipient cells upon uptake. It is hypothesized that M.tb dictates the processes of host EV biogenesis pathways, selectively incorporating its molecules into the host EV to direct immune responses in its favor. During infection with Mtb, both mycobacteria and host cells release EVs. The composition of these EVs varies over time, influenced by the physiological and nutritional state of the host environment. Additionally, different EV populations contribute differently to the pathogenesis of disease at various stages of illness participating in a complex interplay between host cells and pathogens. These interactions ultimately influence immune responses and disease outcomes. However, the precise mechanisms and roles of EVs in pathogenicity and disease outcomes remain to be fully elucidated. In this review, we explored the properties and function of EVs in the context of M.tb infection within the host microenvironment and discussed their capacity as a novel therapeutic strategy to combat tuberculosis.

Cellular and Molecular Mechanisms of Mast Cells in Atherosclerotic Plaque Progression and Destabilization.

Mast cells (MCs) are commonly recognized for their crucial involvement in the pathogenesis of allergic diseases, but over time, it has come to light that they also play a role in the pathophysiology of non-allergic disorders including atherosclerosis. The involvement of MCs in the pathology of atherosclerosis is supported by their accumulation in atherosclerotic plaques upon their progression and the association of intraplaque MC numbers with acute cardiovascular events. MCs that accumulate within the atherosclerotic plaque release a cocktail of mediators through which they contribute to neovascularization, plaque progression, instability, erosion, rupture, and thrombosis. At a molecular level, MC-released proteases, especially cathepsin G, degrade low-density lipoproteins (LDL) and mediate LDL fusion and binding of LDL to proteoglycans (PGs). Through a complicated network of chemokines including CXCL1, MCs promote the recruitment of among others CXCR2+ neutrophils, therefore, aggravating the inflammation of the plaque environment. Additionally, MCs produce extracellular traps which worsen inflammation and contribute to atherothrombosis. Altogether, evidence suggests that MCs actively, via several underlying mechanisms, contribute to atherosclerotic plaque destabilization and acute cardiovascular syndromes, thus, making the study of interventions to modulate MC activation an interesting target for cardiovascular medicine.

Ultrastructural features of tumor-associated mast cells in parasympathetic paragangliomas (chemodectomas) of the neck.

The mechanisms of the pathogenesis of neck paraganglioma (PGL) and the possible role of mast cells (MCs) in its development and metastasis are still poorly understood. We analyzed MCs' morphologic characterization, activation, and the properties of their cytoplasmic/released granules in PGLs, using light and transmission electron microscopy. Paragangliomas showed a large tumor-associated MC population both in the connective tissue layers of the tumor and between the tumor cells. Notably, MCs were presented by a high expression of specific proteases, size variation, polymorphism, and variable ultrastructural phenotype of granules. A massive number of granules were released surrounding the degranulated MCs while the integrity of MC membrane was maintained. Granules were electron-dense with or without a membrane, ranging from 0.2 to 0.8 µm in diameter. MC plasmalemma was not found at the site of MC-collagen fibrils contact, whereas the secretome and fibrils were directly contacted. We observed direct and mediator-based interactions between MCs and paraganglioma cells. The latter preserved their membrane integrity when MC granules were not in proximity. The effects of the MC secretome on the paraganglioma microenvironment demonstrated its pathogenetic role in tumor progression and allow its application to new diagnostic criteria and the development of protocols for personalized therapy. RESEARCH HIGHLIGHTS: Ultrastructural analysis reveals novel regulatory effects of mast cells via diverse secretory pathways on the pathogenesis of parasympathetic paraganglioma, including fibrous extracellular matrix remodeling and mediator-based interactions between MCs and cells of the tumor microenvironment.

Association of Matrix Metalloproteinase-2 (MMP-2) and MMP-9 Promoter Variants, Their Serum Levels, and Activities with Aortic Valve Calcification (AVC) in a Population from Western Iran.

Background: Matrix metalloproteinase (MMP) enzyme gene polymorphisms MMP-2-1575G/A and MMP-9-1562C/T promoter polymorphism, their serum levels, and activity are associated with aortic valve calcification (AVC). Materials and Methods: The synergistic link between the risk of AVC and the alleles T and A of MMP-9 and MMP-2 was investigated, respectively. Ninety-two cases with AVC and 92 healthy individuals from the west of Iran were included, and MMP- 2-1575G/A and MMP-9-1562C/T promoter polymorphisms were detected using PCR-RFLP. The serum levels and activity of MMP-2 and -9 were assessed using ELISA and gelatin zymography methods, respectively. In addition, serum biochemical markers, including FBS, urea and creatinine, cholesterol, triglyceride, HDL, LDL, calcium, phosphorus, and blood pressure: systolic blood pressure and diastolic blood pressure were measured. Results: Heart valve calcification disease was associated with a comparatively higher frequency of the A allele of the MMP2-1575 variation (p = 0.002). In addition, the frequency of T allele of the MMP9-1562 variant was higher than the control group (p = 0.007). Conclusion: MMP-2 and MMP-9 serum levels and activities were observed to be considerably higher in the experimental group than in the control group (p < 0.001). Patients are more susceptible to cardiovascular disease than the control group due to elevated serum levels and activity of MMP-2 and MMP-9.

Effects of silymarin as adjuvant drug on serum levels of CTRP3, anti-cyclic citrullinated peptide (CCP), and high-sensitivity C-reactive protein (hs-CRP) in rheumatoid arthritis patients.

Silymarin is known for its anti-inflammatory and antioxidant properties. We investigated these effects on serum levels of CTRP3, Anti-CCP, and hs-CRP in individuals with Rheumatoid arthritis (RA). In this study, 42 individuals with RA were recruited and their serum specimens were collected, serum levels of hs-CRP, AntiCCP antibodies, and CTRP3 were measured using ELISA. DNA was extracted and investigated for the existence of possible new mutations in the gene encoding CTRP3 using the PCR technique; the desired fragments were then amplified and sequenced. Another blood sample was collected from the case group after taking livergol for three months (3 doses of 140 mg/day) and the tests were repeated. Anti-CCP Abs levels in the postintervention responding group decreased compared to preintervention (p<0.001) while in the non-responding group, the levels increased after the intervention compared to the levels before the intervention (p=0.019). Additionally, CTRP3 levels in the responding group increased postintervention (p=0.003), however, in the non-responding group the levels decreased postintervention when compared to preintervention (p=0.02). The responding group had significantly lower levels of hs-CRP when compared to that of preintervention (p=0.005) whereas the non-responding group had significantly higher levels of postintervention (p<0.001). Moreover, the results of sequencings of exon 6 on CTRP3 gene showed the presence of mutations in exon 6 (position 215:C>T, 338:G>A, 359:A>C, and 153:T>C). Silymarin could be used as an adjuvant in the treatment of rheumatoid arthritis.

Chronic spontaneous urticaria: new evidences on the role of autoimmunity.

PURPOSE OF REVIEW: The purpose of this review is to provide an overview of the recent advancements and relevance of the autoimmune theories in chronic spontaneous urticaria (CSU). RECENT FINDINGS: Two primary types of autoimmunity, Type I and Type IIb, have emerged as major contributors to CSU, characterized by immunoglobulin E (IgE) and immunoglobulin G (IgG) autoantibodies, respectively. Genetic evidence supports the notion that CSU shares more similarities with other autoimmune diseases rather than atopic diseases. Novel autoallergens such as FcεRI and tissue transglutaminase have been identified, contributed to our understanding of autoimmune mechanisms. Furthermore, the potential overlap between Type I and Type IIb autoimmunity has been recognized. Evaluating the autoimmune status of CSU patients through biomarkers and understanding their clinical implications is vital for effective management. For instance, CSU patients with Type IIb autoimmunity, with or without coexisting Type I autoimmunity, may exhibit resistance to H1-antihistamines and omalizumab treatment but could potentially respond well to cyclosporine or Bruton's tyrosine kinase inhibitors. SUMMARY: Further investigations are needed to explore new autoallergens and autoantibodies in CSU, establishing their connection to the development of autoimmunity. The efficacy of novel drugs targeting different mechanisms should be examined to determine their responses in both autoimmune CSU and nonautoimmunity-related CSU.

An update on mechanisms of pruritus and their potential treatment in primary cutaneous T-cell lymphoma.

Primary cutaneous T-cell lymphomas (CTCL), which include mycosis fungoides (MF) and Sézary syndrome (SS), are a group of lymphoproliferative disorders characterized by clonal accumulation of neoplastic T-lymphocytes in the skin. Severe pruritus, one of the most common and distressing symptoms in primary CTCL, can significantly impair emotional well-being, physical functioning, and interpersonal relationships, thus greatly reducing quality of life. Unfortunately, effectively managing pruritus remains challenging in CTCL patients as the underlying mechanisms are, as of yet, not fully understood. Previous studies investigating the mechanisms of itch in CTCL have identified several mediators and their corresponding antagonists used for treatment. However, a comprehensive overview of the mediators and receptors contributing to pruritus in primary CTCL is lacking in the current literature. Here, we summarize and review the mediators and receptors that may contribute to pruritus in primary CTCL to explore the mechanisms of CTCL pruritus and identify effective therapeutic targets using the PubMed and Web of Science databases. Studies were included if they described itch mediators and receptors in MF and SS. Overall, the available data suggest that proteases (mainly tryptase), and neuropeptides (particularly Substance P) may be of greatest interest. At the receptor level, cytokine receptors, MRGPRs, and TRP channels are most likely important. Future drug development efforts should concentrate on targeting these mediators and receptors for the treatment of CTCL pruritus.

How Infection and Vaccination Are Linked to Acute and Chronic Urticaria: A Special Focus on COVID-19.

Since more than a century ago, there has been awareness of the connection between viral infections and the onset and exacerbation of urticaria. Our knowledge about the role of viral infection and vaccination in acute and chronic urticaria improved as a result of the COVID-19 pandemic but it has also highlighted knowledge gaps. Viral infections, especially respiratory tract infections like COVID-19, can trigger the onset of acute urticaria (AU) and the exacerbation of chronic urticaria (CU). Less frequently, vaccination against viruses including SARS-CoV-2 can also lead to new onset urticaria as well as worsening of CU in minority. Here, with a particular focus on COVID-19, we review what is known about the role of viral infections and vaccinations as triggers and causes of acute and chronic urticaria. We also discuss possible mechanistic pathways and outline the unmet needs in our knowledge. Although the underlying mechanisms are not clearly understood, it is believed that viral signals, medications, and stress can activate skin mast cells (MCs). Further studies are needed to fully understand the relevance of viral infections and vaccinations in acute and chronic urticaria and to better clarify causal pathways.

Significance of Mast Cell Formed Extracellular Traps in Microbial Defense.

Mast cells (MCs) are critically involved in microbial defense by releasing antimicrobial peptides (such as cathelicidin LL-37 and defensins) and phagocytosis of microbes. In past years, it has become evident that in addition MCs may eliminate invading pathogens by ejection of web-like structures of DNA strands embedded with proteins known together as extracellular traps (ETs). Upon stimulation of resting MCs with various microorganisms, their products (including superantigens and toxins), or synthetic chemicals, MCs become activated and enter into a multistage process that includes disintegration of the nuclear membrane, release of chromatin into the cytoplasm, adhesion of cytoplasmic granules on the emerging DNA web, and ejection of the complex into the extracellular space. This so-called ETosis is often associated with cell death of the producing MC, and the type of stimulus potentially determines the ratio of surviving vs. killed MCs. Comparison of different microorganisms with specific elimination characteristics such as S pyogenes (eliminated by MCs only through extracellular mechanisms), S aureus (removed by phagocytosis), fungi, and parasites has revealed important aspects of MC extracellular trap (MCET) biology. Molecular studies identified that the formation of MCET depends on NADPH oxidase-generated reactive oxygen species (ROS). In this review, we summarize the present state-of-the-art on the biological relevance of MCETosis, and its underlying molecular and cellular mechanisms. We also provide an overview over the techniques used to study the structure and function of MCETs, including electron microscopy and fluorescence microscopy using specific monoclonal antibodies (mAbs) to detect MCET-associated proteins such as tryptase and histones, and cell-impermeant DNA dyes for labeling of extracellular DNA. Comparing the type and biofunction of further MCET decorating proteins with ETs produced by other immune cells may help provide a better insight into MCET biology in the pathogenesis of autoimmune and inflammatory disorders as well as microbial defense.