Calcium-binding proteins MRP 8 and 14 in a Staphylococcus aureus infection model: role of therapy, inflammation, and infection persistence

Soluble CD163 masks fibronectin-binding protein A-mediated inflammatory activation of Staphylococcus aureus infected monocytes

Binding to fibronectin (FN) is a crucial pathogenic factor of Staphylococcus aureus mediated by fibronectin-binding protein A (FnBP-A) and extracellular adherence protein (Eap). Recently, we have shown that binding of soluble CD163 (sCD163) to FN linked to these molecules exhibits anti-microbial effects by enhancing phagocytosis and killing activity of S. aureus-infected monocytes. However, it remained unclear whether sCD163 also influences the monocytic activation status. Using genetically modified staphylococcal strains we now identified FnBP-A, but not Eap, as activator of the inflammatory response of monocytes to infection. FnBP-A-mediated inflammatory activation was masked by sCD163 binding to S. aureus promoting efficient pathogen elimination. Thus, sCD163 protects monocytes from overwhelming activation upon staphylococcal infection by dampening the secretion of pro-inflammatory cytokines TNFα, IL-1β, IL-6 and IL-8 and DAMP molecule MRP8/14. Moreover, sCD163 limited expression of pro-apoptotic transcription factor NR4A1 induced during S. aureus infection and inhibited induction of chemokine CXCL2promoting survival of staphylococci in vivo. sCD163-mediated effects were not due to general immunosuppression since MAP kinase activation and ROS production were unaltered during infection of monocytes with sCD163-bound bacteria. Thus, sCD163 promotes a specific defence of the immune system against FnBP-A-mediated inflammatory activation enabling successful pathogen elimination, tissue recovery and resolution of inflammation.

Octacalcium phosphate crystals induce inflammation in vivo through interleukin-1 but independent of the NLRP3 inflammasome in mice

OBJECTIVE

To determine the mechanisms involved in inflammatory responses to octacalcium phosphate (OCP) crystals in vivo.

METHODS

OCP crystal-induced inflammation was monitored using a peritoneal model of inflammation in mice with different deficiencies affecting interleukin-1 (IL-1) secretion (IL-1α(-/-) , IL-1β(-/-) , ASC(-/-) , and NLRP3(-/-) mice) or in mice pretreated with IL-1 inhibitors (anakinra [recombinant IL-1 receptor antagonist] and anti-IL-1β). The production of IL-1α, IL-1β, and myeloid-related protein 8 (MRP-8)-MRP-14 complex was determined by enzyme-linked immunosorbent assay. Peritoneal neutrophil recruitment and cell viability were determined by flow cytometry. Depletion of mast cells or resident macrophages was performed by pretreatment with compound 48/80 or clodronate liposomes, respectively.

RESULTS

OCP crystals induced peritoneal inflammation, as demonstrated by neutrophil recruitment and up-modulation of IL-1α, IL-1β, and MRP-8-MRP-14 complex, to levels comparable with those induced by monosodium urate monohydrate crystals. This OCP crystal-induced inflammation was both IL-1α- and IL-1β-dependent, as shown by the inhibitory effects of anakinra and anti-IL-1β antibody treatment. Accordingly, OCP crystal stimulation resulted in milder inflammation in IL-1α(-/-) and IL-1β(-/-) mice. Interestingly, ASC(-/-) and NLRP3(-/-) mice did not show any alteration in their inflammation status in response to OCP crystals. Depletion of the resident macrophage population resulted in a significant decrease in crystal-induced neutrophil infiltration and proinflammatory cytokine production in vivo, whereas mast cell depletion had no effect. Finally, OCP crystals induced apoptosis/necrosis of peritoneal cells in vivo.

CONCLUSION

These data indicate that macrophages, rather than mast cells, are important for initiating and driving OCP crystal-induced inflammation. Additionally, OCP crystals induce IL-1-dependent peritoneal inflammation without requiring the NLRP3 inflammasome.

Damage-associated molecular pattern S100A9 increases bactericidal activity of human neutrophils by enhancing phagocytosis

The damage-associated molecular-pattern S100A9 is found at inflammatory sites in infections and various autoimmune diseases. It is released at very high concentrations in the extracellular milieu by activated neutrophils and monocytes in response to various agents. This proinflammatory protein is found in infected mucosae and tissue abscesses where it acts notably as a potent neutrophil activator. In this study, we examined the role of S100A9 in the control of infections. S100A9 was found to increase human neutrophil bactericidal activity toward Escherichia coli. Although S100A9 induced the accumulation of reactive oxygen species over time through the activation of NADPH oxidase, its antimicrobial activity was mediated mainly by enhancing the efficiency of neutrophil phagocytosis. Interestingly, S100A9 did not act by increasing cell surface expression of CD16, CD32, or CD64 in neutrophils, indicating that its biological effect in FcR-mediated phagocytosis is independent of upregulation of FcγR levels. However, S100A9-induced phagocytic activity required the phosphorylation of Erk1/2, Akt, and Syk. Taken together, our results demonstrate that S100A9 stimulates neutrophil microbicidal activity by promoting phagocytosis.

S-glutathionylation regulates inflammatory activities of S100A9

Reactive oxygen species generated by activated neutrophils can cause oxidative stress and tissue damage. S100A8 (A8) and S100A9 (A9), abundant in neutrophil cytoplasm, are exquisitely sensitive to oxidation, which may alter their functions. Murine A8 is a neutrophil chemoattractant, but it suppresses leukocyte transmigration in the microcirculation when S-nitrosylated. Glutathione (GSH) modulates intracellular redox, and S-glutathionylation can protect susceptible proteins from oxidative damage and regulate function. We characterized S-glutathionylation of A9; GSSG and GSNO generated S-glutathionylated A8 (A8-SSG) and A9 (A9-SSG) in vitro, whereas only A9-SSG was detected in cytosol of neutrophils activated with phorbol myristate acetate (PMA) but not with fMLP or opsonized zymosan. S-Glutathionylation exposed more hydrophobic regions in Zn(2+)-bound A9 but did not alter Zn(2+) binding affinity. A9-SSG had reduced capacity to form heterocomplexes with A8, but the arachidonic acid binding capacities of A8/A9 and A8/A9-SSG were similar. A9 and A8/A9 bind endothelial cells; S-glutathionylation reduced binding. We found little effect of A9 or A9-SSG on neutrophil CD11b/CD18 expression or neutrophil adhesion to endothelial cells. However, A9, A9-SSG and A8/A9 promoted neutrophil adhesion to fibronectin but, in the presence of A8, A9-mediated adhesion was abrogated by glutathionylation. S-Glutathionylation of A9 may protect its oxidation to higher oligomers and reduce neutrophil binding to the extracellular matrix. This may regulate the magnitude of neutrophil migration in the extravasculature, and together with the functional changes we reported for S-nitrosylated A8, particular oxidative modifications of these proteins may limit tissue damage in acute inflammation.

S100 calgranulin proteins S100A8, S100A9 and S100A12 are expressed in the inflamed gastric mucosa of Helicobacter pylori-infected children

The expression of the inflammatory S100 calgranulin proteins (S100A8, S100A9 and S100A12) in normal and Helicobacter pylori-infected gastric mucosa of children were examined. S100A8, S100A9 and S100A12, which were virtually absent in normal gastric mucosa, were highly expressed in H pylori-infected mucosa. This expression correlated with the severity of gastritis (r=0.9422, P<0.05). S100 calgranulins may be involved in bacterial-induced gastritis and may limit bacterial growth.

Gene expression patterns in blood leukocytes discriminate patients with acute infections

Each infectious agent represents a unique combination of pathogen-associated molecular patterns that interact with specific pattern-recognition receptors expressed on immune cells. Therefore, we surmised that the blood immune cells of individuals with different infections might bear discriminative transcriptional signatures. Gene expression profiles were obtained for 131 peripheral blood samples from pediatric patients with acute infections caused by influenza A virus, Gram-negative (Escherichia coli) or Gram-positive (Staphylococcus aureus and Streptococcus pneumoniae) bacteria. Thirty-five genes were identified that best discriminate patients with influenza A virus infection from patients with either E coli or S pneumoniae infection. These genes classified with 95% accuracy (35 of 37 samples) an independent set of patients with either influenza A, E coli, or S pneumoniae infection. A different signature discriminated patients with E coli versus S aureus infections with 85% accuracy (34 of 40). Furthermore, distinctive gene expression patterns were observed in patients presenting with respiratory infections of different etiologies. Thus, microarray analyses of patient peripheral blood leukocytes might assist in the differential diagnosis of infectious diseases.

Gingival crevicular fluid levels of calprotectin and myeloperoxidase during therapy for generalized aggressive periodontitis

BACKGROUND

Levels of the inflammation marker calprotectin in gingival crevicular fluid correspond to clinical and biochemical parameters of periodontal inflammation. Neutrophil granulocytes (polymorphonuclear neutrophils: PMNs) are supposed to be the main source of calprotectin in gingival crevicular fluid, but evidence is still lacking. The influence of periodontal therapy on gingival crevicular fluid levels of calprotectin has not yet been determined.

OBJECTIVES

Gingival crevicular fluid levels of calprotectin were monitored during therapy for generalized aggressive periodontitis. Interrelations between calprotectin and the PMN marker myeloperoxidase (MPO) were evaluated.

MATERIAL AND METHODS

Gingival crevicular fluid samples were collected from 23 patients with generalized aggressive periodontitis before and 3 months after non-surgical therapy with an adjunctive antimicrobial medication. Clinical parameters were recorded with a pressure-calibrated electronic probe. Levels of calprotectin and MPO in gingival crevicular fluid were analysed by enzyme-linked immunosorbent assay (ELISA) procedures.

RESULTS

At baseline, levels of calprotectin and MPO were highly correlated. Bleeding and suppurating sites showed significantly higher levels of calprotectin and MPO than non-bleeding, non-suppurating sites. Therapy significantly decreased levels of both biomarkers. These changes of calprotectin and MPO were highly correlated and also related to probing-depth reduction. Three months after therapy, the levels of both markers still showed significant correlations in initially deep sites, whereas in initially shallow sites no significant correlation was found. After therapy, levels of markers in bleeding and non-bleeding sites were comparable.

CONCLUSION

The correlations between calprotectin and MPO indicate that PMNs are a major contributor to the calprotectin content in gingival crevicular fluid of severely affected sites. Calprotectin levels in gingival crevicular fluid and their changes reflect periodontal inflammation as well as the clinical treatment outcome. A prognostic potential of this marker substance remains to be determined.