[Unintended Observations Leading to Macrophage Growth and Neutrophil Factor Research].

My research area in the pharmaceutical industry is innate immunity, especially in phagocytic cells. First, I studied the heat-stable growth factor of peripheral macrophages in tumorous ascitic fluid and found that lipoproteins are an influencing factor. Later, my colleagues and I found that lipid-containing substances, namely, oxidized low-density lipoprotein, dead neutrophils, or purified lipids that could be scavenged by macrophages, induce their growth. From the series of this study, I concluded that phagocytic substances induce macrophage growth by autocrine stimulation of granulocyte-macrophage colony-stimulating factor (GM-CSF). During the study, we found that neutrophils have growth-inhibitory effects against a variety of cells. Then, I elucidated that the primary factor is a zinc-binding protein, calprotectin, an abundant protein complex in the neutrophil cytosol. I found that calprotectin induces apoptosis in many cell types, including tumor cells and normal fibroblasts, and that the zinc-binding capacity is essential for its activity. Microscopic observations revealed that neutrophil extract contains factor-inducing three-dimensional cell aggregation of human mammary carcinoma, MCF-7. I elucidated that cathepsin G is responsible for this activity and that its effect is dependent on the activation of insulin-like growth factor-1. I believe that this modest, albeit novel, observation was crucial to my thirty-nine-year-long career researching phagocytic cells.

The Zinc Transporter ZnuABC Is Critical for the Virulence of Chromobacterium violaceum and Contributes to Diverse Zinc-Dependent Physiological Processes.

Chromobacterium violaceum is a ubiquitous environmental bacterium that causes sporadic life-threatening infections in humans. How C. violaceum acquires zinc to colonize environmental and host niches is unknown. In this work, we demonstrated that C. violaceum employs the zinc uptake system ZnuABC to overcome zinc limitation in the host, ensuring the zinc supply for several physiological demands. Our data indicated that the C. violaceum ZnuABC transporter is encoded in a zur-CV_RS15045-CV_RS15040-znuCBA operon. This operon was repressed by the zinc uptake regulator Zur and derepressed in the presence of the host protein calprotectin (CP) and the synthetic metal chelator EDTA. A ΔznuCBA mutant strain showed impaired growth under these zinc-chelated conditions. Moreover, the deletion of znuCBA provoked reductions in violacein production, swimming motility, biofilm formation, and bacterial competition. Remarkably, the ΔznuCBA mutant strain was highly attenuated for virulence in an in vivo mouse infection model and showed low capacities to colonize the liver, grow in the presence of CP, and resist neutrophil killing. Overall, our findings demonstrate that ZnuABC is essential for C. violaceum virulence, contributing to subversion of zinc-based host nutritional immunity.

Modifying gut integrity and microbiome in children with severe acute malnutrition using legume-based feeds (MIMBLE): A pilot trial.

Case fatality among African children with severe acute malnutrition remains high. We report a 3-arm pilot trial in 58 Ugandan children, comparing feeds targeting disordered gastrointestinal function containing cowpea (CpF, n = 20) or inulin (InF, n = 20) with conventional feeds (ConF, n = 18). Baseline measurements of gut permeability (lactulose:mannitol ratio 1.19 ± SD 2.00), inflammation (fecal calprotectin 539.0 µg/g, interquartile range [IQR] 904.8), and satiety (plasma polypeptide YY 62.6 pmol/l, IQR 110.3) confirm gastrointestinal dysfunction. By day 28, no differences are observable in proportion achieving weight gain >5 g/kg/day (87%, 92%, 86%; p > 0.05), mortality (16%, 30%, 17%; p > 0.05), or edema resolution (83%, 54%, 91%; p > 0.05) among CpF, InF, and ConF. Decreased fecal bacterial richness from day 1 (abundance-based coverage estimator [ACE] 53.2) to day 7 (ACE 40.8) is observed only in ConF (p = 0.025). Bifidobacterium relative abundance increases from day 7 (5.8% ± 8.6%) to day 28 (10.9% ± 8.7%) in CpF (corrected p = 1.000). Legume-enriched feeds support aspects of gut function and the microbiome. Trial registration PACTR201805003381361.

Multi-metal nutrient restriction and crosstalk in metallostasis systems in microbial pathogens.

Transition metals from manganese to zinc function as catalytic and structural cofactors for an amazing diversity of proteins and enzymes, and thus are essential for all forms of life. During infection, inflammatory host proteins limit the accessibility of multiple transition metals to invading pathogens in a process termed nutritional immunity. In order to respond to host-mediated metal starvation, bacteria employ both protein and RNA-based mechanisms to sense prevailing transition metal concentrations that collectively regulate systems-level strategies to maintain cellular metallostasis. In this review, we discuss a number of recent advances in our understanding of how bacteria orchestrate the adaptive response to host-mediated multi-metal restriction, highlighting crosstalk among these regulatory systems.

The Innate Immune Protein S100A9 Protects from T-Helper Cell Type 2-mediated Allergic Airway Inflammation.

Calprotectin is a heterodimer of the proteins S100A8 and S100A9, and it is an abundant innate immune protein associated with inflammation. In humans, calprotectin transcription and protein abundance are associated with asthma and disease severity. However, mechanistic studies in experimental asthma models have been inconclusive, identifying both protective and pathogenic effects of calprotectin. To clarify the role of calprotectin in asthma, calprotectin-deficient S100A9-/- and wild-type (WT) C57BL/6 mice were compared in a murine model of allergic airway inflammation. Mice were intranasally challenged with extracts of the clinically relevant allergen, Alternaria alternata (Alt Ext), or PBS every third day over 9 days. On Day 10, BAL fluid and lung tissue homogenates were harvested and allergic airway inflammation was assessed. Alt Ext challenge induced release of S100A8/S100A9 to the alveolar space and increased protein expression in the alveolar epithelium of WT mice. Compared with WT mice, S100A9-/- mice displayed significantly enhanced allergic airway inflammation, including production of IL-13, CCL11, CCL24, serum IgE, eosinophil recruitment, and airway resistance and elastance. In response to Alt Ext, S100A9-/- mice accumulated significantly more IL-13+IL-5+CD4+ T-helper type 2 cells. S100A9-/- mice also accumulated a significantly lower proportion of CD4+ T regulatory (Treg) cells in the lung that had significantly lower expression of CD25. Calprotectin enhanced WT Treg cell suppressive activity in vitro. Therefore, this study identifies a role for the innate immune protein, S100A9, in protection from CD4+ T-helper type 2 cell hyperinflammation in response to Alt Ext. This protection is mediated, at least in part, by CD4+ Treg cell function.

Calprotectin in rheumatic diseases.

Calprotectin is a heterodimer formed by two proteins, S100A8 and S100A9, which are mainly produced by activated monocytes and neutrophils in the circulation and in inflamed tissues. The implication of calprotectin in the inflammatory process has already been demonstrated, but its role in the pathogenesis, diagnosis, and monitoring of rheumatic diseases has gained great attention in recent years. Calprotectin, being stable at room temperature, is a candidate biomarker for the follow-up of disease activity in many autoimmune disorders, where it can predict response to treatment or disease relapse. There is evidence that a number of immunomodulators, including TNF-α inhibitors, may reduce calprotectin expression. S100A8 and S100A9 have a potential role as a target of treatment in murine models of autoimmune disorders, since the direct or indirect blockade of these proteins results in amelioration of the disease process. In this review, we will go over the biologic functions of calprotectin which might be involved in the etiology of rheumatic disorders. We will also report evidence of its potential use as a disease biomarker. Impact statement Calprotectin is an acute-phase protein produced by monocytes and neutrophils in the circulation and inflamed tissues. Calprotectin seems to be more sensitive than CRP, being able to detect minimal residual inflammation and is a candidate biomarker in inflammatory diseases. High serum levels are associated with some severe manifestations of rheumatic diseases, such as glomerulonephritis and lung fibrosis. Calprotectin levels in other fluids, such as saliva and synovial fluid, might be helpful in the diagnosis of rheumatic diseases. Of interest is also the potential role of calprotectin as a target of treatment.

Human calprotectin is an iron-sequestering host-defense protein.

Human calprotectin (CP) is a metal-chelating antimicrobial protein of the innate immune response. The current working model states that CP sequesters manganese and zinc from pathogens. We report the discovery that CP chelates iron and deprives bacteria of this essential nutrient. Elemental analysis of CP-treated growth medium establishes that CP reduces the concentrations of manganese, iron and zinc. Microbial growth studies reveal that iron depletion by CP contributes to the growth inhibition of bacterial pathogens. Biochemical investigations demonstrate that CP coordinates Fe(II) at an unusual hexahistidine motif, and the Mössbauer spectrum of (57)Fe(II)-bound CP is consistent with coordination of high-spin Fe(II) at this site (δ = 1.20 mm/s, ΔEQ = 1.78 mm/s). In the presence of Ca(II), CP turns on its iron-sequestering function and exhibits subpicomolar affinity for Fe(II). Our findings expand the biological coordination chemistry of iron and support a previously unappreciated role for CP in mammalian iron homeostasis.

Oxidation of calprotectin by hypochlorous acid prevents chelation of essential metal ions and allows bacterial growth: Relevance to infections in cystic fibrosis.

Calprotectin provides nutritional immunity by sequestering manganese and zinc ions. It is abundant in the lungs of patients with cystic fibrosis but fails to prevent their recurrent infections. Calprotectin is a major protein of neutrophils and composed of two monomers, S100A8 and S100A9. We show that the ability of calprotectin to limit growth of Staphylococcus aureus and Pseudomonas aeruginosa is exquisitely sensitive to oxidation by hypochlorous acid. The N-terminal cysteine residue on S100A9 was highly susceptible to oxidation which resulted in cross-linking of the protein monomers. The N-terminal methionine of S100A8 was also readily oxidized by hypochlorous acid, forming both the methionine sulfoxide and the unique product dehydromethionine. Isolated human neutrophils formed these modifications on calprotectin when their myeloperoxidase generated hypochlorous acid. Up to 90% of the N-terminal amine on S100A8 in bronchoalveolar lavage fluid from young children with cystic fibrosis was oxidized. Oxidized calprotectin was higher in children with cystic fibrosis compared to disease controls, and further elevated in those patients with infections. Our data suggest that oxidative stress associated with inflammation in cystic fibrosis will stop metal sequestration by calprotectin. Consequently, strategies aimed at blocking extracellular myeloperoxidase activity should enable calprotectin to provide nutritional immunity within the airways.

[Research advances in the role of fecal calprotectin in intestinal development and diseases among children].

Calprotectin is a calcium- and zinc-binding protein of the S100 family expressed mainly by neutrophils with important extracellular activity. This paper reviews current findings concerning the relationship between faecal calprotectin and intestinal development among children, influencing factors of fecal calprotectin and the implication of faecal calprotectin in the diagnosis, follow-up, assessment of relapses, and response to treatment in pediatric intestinal diseases, such as necrotizing enterocolitis, inflammatory bowel disease, intestinal infection, celiac disease and allergy. Further studies are required to provide insights into the actual role of calprotectin in physiological and pathological processes in pediatrics.

Calprotectin and cardiovascular events. A narrative review.

OBJECTIVES: Calprotectin, also known as S100A8/A9 complex, is currently considered as a valid biomarker for diagnosis, follow-up and therapeutic monitoring of inflammatory bowel diseases. The attractive evidence that this protein may be actively produced and released by leukocytes (especially neutrophils) and by nonmyeloid cardiovascular cell types has paved the way to a series of studies that have assessed its biology in the setting of cardiovascular disease. The aim of this review was thus to investigate the diagnostic and prognostic utility of this biomarker in cardiovascular disease and in particular in myocardial infarction. DESIGN AND METHODS: We performed a systematic, electronic search on Medline, Scosus and Web of Science, using the keywords "calprotectin" or "S100A8/A9" or "MRP-8/14" and "myocardial infarction" or "acute coronary syndrome" or "cardiovascular disease", from inception to June 2013. The bibliographic references of articles published in English, French and Italian were reviewed for additional relevant studies. RESULTS: The data of the current scientific literature seems to confirm that calprotectin is actively secreted in the setting of cardiac ischemia and its concentration is significantly associated with the prognosis. Nevertheless, the evidence provided by recent articles that have assessed its performance for diagnosing acute myocardial infarction, either alone or in combination with troponin, supports the hypothesis that this biomarker may be of limited value for enabling a better or faster diagnosis of cardiac ischemia. Even its putative role as an independent prognostic biomarker of cardiovascular morbidity and death is still largely uncertain. CONCLUSIONS: It can hence be concluded that calprotectin does not currently meet the requirements for efficient diagnosis and prognostication of patients with cardiovascular disease.

Role of calprotectin in cardiometabolic diseases.

Calprotectin represents an interesting peptide known to be involved in the pathophysiology of various inflammatory processes. Being secreted from activated neutrophils and monocytes under various conditions, it can also be found in the extracellular fluids and serve as a biomarker of ongoing inflammation, which property is currently used in the monitoring of inflammatory bowel diseases. Recent studies, however, suggest that calprotectin could serve as an important prognostic factor for cardiovascular and cardiometabolic diseases, since these are occurring on the basis of low-grade chronic inflammation. We assume that calprotectin may represent a useful marker in predicting the course of atherosclerotic process, coronary artery disease and acute coronary syndromes. Our review is focused on the importance of calprotectin in the diagnosis and prognostic stratification in the field of cardiometabolic risk.

Association among vitamin D, oral candidiasis, and calprotectinemia in HIV.

Vitamin D deficiency is associated with negative health outcomes, including infections. Vitamin D modulates inflammation and down-regulates the expression of calprotectin, a molecule which influences neutrophil functions and which has been linked to oral candidiasis (OC), the most prevalent oral lesion in human immunodeficiency virus (HIV). We hypothesized a positive association between vitamin D deficiency and OC, and that this effect was partially modulated by calprotectinemia. Plasma calprotectin and serum 25 (OH) vitamin D levels were measured in stored samples from 84 HIV-seropositive Chicago women enrolled in the Oral Substudy of the Women's Interagency HIV Study (WIHS). OC and vitamin D deficiency were diagnosed in, respectively, 14 (16.7%) and 46 (54.8%) of those studied. Vitamin D deficiency was positively associated with OC (p = 0.011) and with higher calprotectinemia (p = 0.019) in univariate analysis. After adjustment for CD4, HIV viral load, HIV treatment, and tobacco and heroin/methadone use, vitamin D deficiency remained a significant predictor of OC (OR 5.66; 95% confidence interval 1.01-31.71). This association weakened after adjustment for calprotectinemia, supporting a role for calprotectinemia as a moderator of this effect. These findings support studies to examine the effect of vitamin D status on calprotectinemia, neutrophil functions, and opportunistic mucosal infections in HIV.

Effect of 1-year anti-TNF-α therapy on aortic stiffness, carotid atherosclerosis, and calprotectin in inflammatory arthropathies: a controlled study.

BACKGROUND: Premature arterial stiffening and atherosclerosis are increased in patients with inflammatory arthropathies such as rheumatoid arthritis (RA), ankylosing spondylitis (AS) and psoriatic arthritis (PsA). The proinflammatory protein calprotectin is associated with inflammatory arthropathies, vascular pathology, and acute coronary events. We examined the long-term effects of treatment with tumor necrosis factor (TNF)-α antagonists on aortic stiffness and carotid intima media thickness (CIMT) in patients with inflammatory arthropathies, and the relationships to the levels of calprotectin. METHODS: Fifty-five patients with RA, AS, or PsA and a clinical indication for anti-TNF-α therapy were included and followed with regular examinations for 1 year. Thirty-six patients starting with anti-TNF-α therapy were compared with a nontreatment group of 19 patients. Examinations included assessments of aortic stiffness (aortic pulse wave velocity, aPWV), CIMT, and plasma calprotectin. RESULTS: After 1 year, aPWV (mean (s.d.)) was improved in the treatment group, but not in the control group (-0.54 [0.79] m/s vs. 0.06 [0.61] m/s, respectively; P = 0.004), and CIMT progression (median (quartile cut-points, 25th and 75th percentiles)) was reduced in the treatment group compared to the control group (-0.002 [-0.038, 0.030] mm vs. 0.030 [0.011, 0.043] mm, respectively; P = 0.01). In multivariable analyses, anti-TNF-α therapy over time was associated with improved aPWV (P = 0.02) and reduced CIMT progression (P = 0.04), and calprotectin was longitudinally associated with aPWV (P = 0.02). CONCLUSIONS: Long-term anti-TNF-α therapy improved aortic stiffness and CIMT progression in patients with inflammatory arthropathies. Calprotectin may be a soluble biomarker reflecting aortic stiffening in these patients.

Detection of calprotectin and apoptotic activity within the equine colon from horses with black walnut extract-induced laminitis.

The black walnut extract (BWE) model of equine laminitis is associated with a systemic inflammatory response manifest by increased expression of inflammatory cytokines in the lungs and liver as well as the laminae. The specific role of the gastrointestinal tract in development of this response is unclear and is of utmost importance, as gastrointestinal disease and laminitis are intimately related. We investigated calprotectin expression and epithelial and endothelial apoptosis in the colon of horses exposed to orally administered BWE. Sections of colon from 19 horses including 7 controls not exposed to BWE, 6 horses at the developmental time-point of leukopenia (DTP) and 6 at the onset of Obel grade 1 laminitis (LAM) after BWE-administration were histologically examined. Immunohistochemical evaluation for calprotectin expression with MAC 387 antibody was performed along with assessment of epithelial and endothelial apoptosis with caspase-3 active antibody. Calprotectin expression and percentage of apoptotic cells were compared between controls and the two treatment groups and presence of a correlation between calprotectin expression and apoptosis was evaluated. Histological findings from BWE-treated horses included eosinophil and lymphocyte epitheliotropism. The DTP group had a higher (p<0.01) calprotectin score with respect to the control group, while there was no significant difference in percentage of epithelial and endothelial apoptotic cells between groups (p=0.08 and p=0.48 respectively). No significant correlation was found between calprotectin score and epithelial or endothelial apoptosis (p=0.69 and p=0.29 respectively). There is preliminary evidence that exposure of horses to BWE results in an early inflammatory response in the colon. Further studies are needed to characterize the nature of the colonic injury in BWE-exposed horses and the link to the development of laminitis.

Neural cell-cell and cell-substrate adhesion through N-cadherin, N-CAM and L1.

In this study neural (N)-cadherin, neural cell adhesion molecule (N-CAM) and L1 proteins and their antibody equivalents were covalently immobilized on a polyethylene-imine (PEI)-coated glass surface to form neuron-adhesive coatings. Impedance sensing and (supplementary) image analysis were used to monitor the effects of these CAMs. Immobilization of high concentrations of both N-cadherin protein and antibody led to good adhesion of neurons to the modified surface, better than surfaces treated with 30.0 and 100.0 µg ml(-1) N-CAM protein and antibody. L1 antibody and protein coating revealed no significant effect on neuronal cell-substrate adhesion. In a second series of combinatorial experiments, we used the same antibodies and proteins as medium-additives to inhibit cell-cell adhesion between neurons. Adhesion of neurons cultured on N-cadherin protein or antibody-modified surfaces was lowered by the addition of a soluble N-cadherin protein and antibody to the culturing medium, accelerating neuronal aggregation. The presence of a soluble N-CAM antibody or protein had no effect on the adhesion of neuronal cells on a N-cadherin protein-modified surface. On a N-cadherin antibody-coated surface, the addition of a soluble N-CAM protein led to cell death of neurons after 48 h, while a N-CAM antibody had no effect. In the presence of a soluble N-cadherin protein and antibody the aggregation of neurons was inhibited, both on N-CAM protein and N-CAM antibody-modified surfaces. Neurons cultured on immobilized antibodies were less affected by the addition of soluble CAM blockers than neurons cultured on immobilized proteins, indicating that antibody-protein bonds are more stable compared to protein-protein bonds.

[Faecal calprotectin in inflammatory bowel diseases: review]. / Place de la calprotectine fécale au cours des maladies inflammatoires chroniques de l'intestin : mise au point.

BACKGROUND: The clinical course of inflammatory bowel disease (IBD) is characterised by a succession of relapses and remissions. A regular and a long term monitoring of such patients is required. Faecal markers, especially calprotectin's use, seem to be useful in these patients. Faecal calprotectin is a reliable maker of intestinal inflammation in IBD. Its level is assessed by a simple and a non invasive test. AIM: We proposed to review main indications and study results of faecal calprotectin test use in IBD patients. METHODS: Review of literature. RESULTS: Faecal calprotectin assessment isn't an IBD specific test. Selective use is required to have a good benefit-cost ratio. Prediction of relapses in asymptomatic patients as well as post operative reccurence seems to be the main indications for its use. CONCLUSION: Mucosal healing assessment after anti-TNF treatment can also be an interesting indication although it isn't well evaluated.

Faecal calprotectin in the diagnosis of inflammatory bowel disease.

Suspicion of inflammatory bowel disease should be raised in any patient with chronic or recurrent abdominal pain and diarrhoea. However, symptoms of inflammatory bowel disease (IBD) overlap with functional gastrointestinal disorders and those patients may not need endoscopy. Currently, colonoscopy with multiple biopsies is considered the gold standard to establish the diagnosis of IBD. Unfortunately, patient selection for endoscopy based on symptoms is not reliable. The use of guidelines of appropriateness for endoscopy yields significantly more significant findings but the selection criteria suffer from low specificity. Calprotectin is a calcium binding protein of neutrophil granulocytes that correlates well with neutrophil infiltration of the intestinal mucosa when measured in faeces. In the last decade, a large body of evidence on the diagnostic value of faecal calprotectin has accumulated and measurement of calprotectin in faeces has been suggested as a surrogate marker of intestinal inflammation. Testing of faecal calprotectin has been highly useful to distinguish organic from functional intestinal disorders in patients with abdominal complaints. Additionally, faecal calprotectin has reliably identified colonic inflammation in patients with suspected IBD. The use of this inexpensive and widely available test in the evaluation and risk stratification in patients with abdominal complaints is likely to increase in the future.

The role of calprotectin in obstetrics and gynecology.

The purpose of this article is to create the first complete review concerning the role of calprotectin, a calcium- and zinc-binding protein of the S100/calgranulins family, in obstetrics and gynecology. A Medline search was conducted between 6 and 8 June 2009 using the term calprotectin and its synonyms combined with the following ones: calprotectin, obstetrics and gynecology, breast cancer, ovarian cancer, endometrial cancer, cervical cancer, menstrual cycle, pregnancy, fetal implantation, labor, intra-amniotic inflammation, preeclampsia, HELLP syndrome, Rh(-) incompatibility. We found 46 studies which referred to obstetrics and gynecology. We excluded 11 studies which referred to obstetrics and gynecology but did not include enough information about calprotectin, and another two which referred to calprotectin but were not related to subjects of obstetrics and gynecology. Thus, we ended up with 33 studies which contained sufficient information to extract data for this review. All the articles were written in English. It was found that calprotectin is associated with many physiologic and pathologic processes in obstetrics and gynecology, such as: breast cancer, ovarian cancer, endometrial cancer, cervical cancer, cervical and vaginal physiology, menstrual cycle, pregnancy and labor. The role of calprotectin in these conditions is significant. In conclusion, the role of calprotectin seems to be important in several issues of obstetrics and gynecology. For example, calprotectin could be used as a diagnostic, prognostic or metastatic marker in several types of cancer, as a marker of inflammation and as a pharmaceutical target in many conditions. Further studies must be conducted to elucidate this role.

Transamidation by transglutaminase 2 transforms S100A11 calgranulin into a procatabolic cytokine for chondrocytes.

In osteoarthritis (OA), low-grade joint inflammation promotes altered chondrocyte differentiation and cartilage catabolism. S100/calgranulins share conserved calcium-binding EF-hand domains, associate noncovalently as homodimers and heterodimers, and are secreted and bind receptor for advanced glycation end products (RAGE). Chondrocyte RAGE expression and S100A11 release are stimulated by IL-1beta in vitro and increase in OA cartilage in situ. Exogenous S100A11 stimulates chondrocyte hypertrophic differentiation. Moreover, S100A11 is covalently cross-linked by transamidation catalyzed by transglutaminase 2 (TG2), itself an inflammation-regulated and redox stress-inducible mediator of chondrocyte hypertrophic differentiation. In this study, we researched mouse femoral head articular cartilage explants and knee chondrocytes, and a soluble recombinant double point mutant (K3R/Q102N) of S100A11 TG2 transamidation substrate sites. Both TG2 and RAGE knockout cartilage explants retained IL-1beta responsiveness. The K3R/Q102N mutant of S100A11 retained the capacity to bind to RAGE and chondrocytes but lost the capacity to signal via the p38 MAPK pathway or induce chondrocyte hypertrophy and glycosaminoglycans release. S100A11 failed to induce hypertrophy, glycosaminoglycan release, and appearance of the aggrecanase neoepitope NITEGE in both RAGE and TG2 knockout cartilages. We conclude that transamidation by TG2 transforms S100A11 into a covalently bonded homodimer that acquires the capacity to signal through the p38 MAPK pathway, accelerate chondrocyte hypertrophy and matrix catabolism, and thereby couple inflammation with chondrocyte activation to potentially promote OA progression.