Murine antigen-induced inflammation--a model for studying induction, resolution and the adaptive phase of inflammation

Zymosan-Induced Murine Peritonitis Is Associated with an Increased Sphingolipid Synthesis without Changing the Long to Very Long Chain Ceramide Ratio

Sphingolipids are key molecules in inflammation and defense against pathogens. Their role in dectin-1/TLR2-mediated responses is, however, poorly understood. This study investigated the sphingolipidome in the peritoneal fluid, peritoneal cells, plasma, and spleens of mice after intraperitoneal injection of 0.1 mg zymosan/mouse or PBS as a control. Samples were collected at 2, 4, 8, and 16 h post-injection, using a total of 36 mice. Flow cytometry analysis of peritoneal cells and measurement of IL-6, IL-1β, and TNF-α levels in the peritoneal lavages confirmed zymosan-induced peritonitis. The concentrations of sphingoid bases, dihydroceramides, ceramides, dihydrosphingomyelins, sphingomyelins, monohexosylceramides, and lactosylceramides were increased after zymosan administration, and the effects varied with the time and the matrix measured. The greatest changes occurred in peritoneal cells, followed by peritoneal fluid, at 8 h and 4 h post-injection, respectively. Analysis of the sphingolipidome suggests that zymosan increased the de novo synthesis of sphingolipids without change in the C14-C18:C20-C26 ceramide ratio. At 16 h post-injection, glycosylceramides remained higher in treated than in control mice. A minor effect of zymosan was observed in plasma, whereas sphinganine, dihydrosphingomyelins, and monohexosylceramides were significantly increased in the spleen 16 h post-injection. The consequences of the observed changes in the sphingolipidome remain to be established.

Chemokine (C-C motif) ligand 2 and coronary artery disease: Tissue expression of functional and atypical receptors

Chemokines, particularly chemokine (C-C- motif) ligand 2 (CCL2), control leukocyte migration into the wall of the artery and regulate the traffic of inflammatory cells. CCL2 is bound to functional receptors (CCR2), but also to atypical chemokine receptors (ACKRs), which do not induce cell migration but can modify chemokine gradients. Whether atherosclerosis alters CCL2 function by influencing the expression of these receptors remains unknown. In a necropsy study, we used immunohistochemistry to explore where and to what extent CCL2 and related receptors are present in diseased arteries that caused the death of men with coronary artery disease compared with unaffected arteries. CCL2 was marginally detected in normal arteries but was more frequently found in the intima. The expression of CCL2 and related receptors was significantly increased in diseased arteries with relative differences among the artery layers. The highest relative increases were those of CCL2 and ACKR1. CCL2 expression was associated with a significant predictive value of atherosclerosis. Findings suggest the need for further insight into receptor specificity or activity and the interplay among chemokines. CCL2-associated conventional and atypical receptors are overexpressed in atherosclerotic arteries, and these may suggest new potential therapeutic targets to locally modify the overall anti-inflammatory response.

Early Peritoneal CC Chemokine Production Correlates with Divergent Inflammatory Phenotypes and Susceptibility to Experimental Arthritis in Mice

The inflammatory and autoimmune events preceding clinical symptoms in rheumatoid arthritis (RA) and other autoimmune diseases are difficult to study in human patients. Therefore, animal models that share immunologic and clinical features with human RA, such as pristane-induced arthritis (PIA), are valuable tools for assessing the primordial events related to arthritis susceptibility. PIA-resistant HIII and susceptible LIII mice were injected i.p. with pristane, and peritoneal lavage fluid was harvested in the early (7 days) and late (35 days) preclinical phases of PIA. Chemokine and cytokine levels were measured in lavage supernatant with ELISA, peritoneal inflammatory leukocytes were immunophenotyped by flow cytometry, and gene expression was determined by qRT-PCR. Leukocyte recruitment was quantitatively and qualitatively divergent in the peritoneum of HIII and LIII mice, with an early increase of CC chemokines (CCL2/CCL3/CCL5/CCL12/CCL22) in the susceptible LIII strain. Also, cytokines such as IL-12p40, IL-23, and IL-18 were elevated in LIII mice while IL-6 was increased in HIII animals. The results show that an early peritoneal CC chemokine response is an important feature of arthritis susceptibility and defines potential biomarkers in this model.

Natural killer cells play an essential role in resolution of antigen-induced inflammation in mice

This study examined whether NK cells are important for resolution of antigen-induced inflammation. C57BL/6 mice were immunized twice with methylated BSA (mBSA) and inflammation induced by intraperitoneal injection of mBSA. Mice were injected intravenously with anti-asialo GM1 (αASGM1) or a control antibody 24h prior to peritonitis induction and peritoneal exudate collected at different time points. Expression of surface molecules and apoptosis on peritoneal cells was determined by flow cytometry and concentration of chemokines, cytokines, soluble cytokine receptors and lipid mediators by ELISA and LC-MS/MS. Apoptosis in parathymic lymph nodes and spleens was determined by TUNEL staining. Mice administered αASGM1 had lower peritoneal NK cell numbers and a higher number of peritoneal neutrophils 12h after induction of inflammation than control mice. The number of neutrophils was still high in the αASGM1 treated mice when their number had returned to baseline levels in the control mice, 48h after induction of inflammation. Peritoneal concentrations of the neutrophil regulators G-CSF and IL-12p40 were higher at 12h in the αASGM1 treated mice than in the control mice, whereas concentrations of lipid mediators implicated in resolution of inflammation, i.e. LXA₄ and PGE₂, were lower. Reduced apoptosis was detected in peritoneal neutrophils as well as in draining lymph nodes and spleens from the αASGM1 treated mice compared with that in the control mice. In addition, αASGM1 treated mice had lower number of peritoneal NK cells expressing NKp46 and NKG2D, receptors implicated in NK cell-induced neutrophil apoptosis. Furthermore, αASGM1 treatment completely blocked the increase in CD27⁺ NK cells that occurred in control mice following induction of inflammation, but CD27⁺ NK cells have been suggested to have a regulatory role. These results indicate a crucial role for NK cells in resolution of antigen-induced inflammation and suggest their importance in tempering neutrophil recruitment and maintaining neutrophil apoptosis.

A Novel Subset of Anti-Inflammatory CD138+ Macrophages Is Deficient in Mice with Experimental Lupus

Dead cells accumulating in the tissues may contribute to chronic inflammation. We examined the cause of impaired apoptotic cell clearance in human and murine lupus. Dead cells accumulated in bone marrow from lupus patients but not from nonautoimmune patients undergoing myeloablation, where they were efficiently removed by macrophages (MΦ). Impaired apoptotic cell uptake by MΦ also was seen in mice treated i.p. with pristane (develop lupus) but not mineral oil (MO) (do not develop lupus). The inflammatory response to both pristane and MO rapidly depleted resident (Tim4⁺) large peritoneal MΦ. The peritoneal exudate of pristane-treated mice contained mainly Ly6C^hi inflammatory monocytes; whereas in MO-treated mice, it consisted predominantly of a novel subset of highly phagocytic MΦ resembling small peritoneal MΦ (SPM) that expressed CD138⁺ and the scavenger receptor Marco. Treatment with anti-Marco-neutralizing Abs and the class A scavenger receptor antagonist polyinosinic acid inhibited phagocytosis of apoptotic cells by CD138⁺ MΦ. CD138⁺ MΦ expressed IL-10R, CD206, and CCR2 but little TNF-α or CX3CR1. They also expressed high levels of activated CREB, a transcription factor implicated in generating alternatively activated MΦ. Similar cells were identified in the spleen and lung of MO-treated mice and also were induced by LPS. We conclude that highly phagocytic, CD138⁺ SPM-like cells with an anti-inflammatory phenotype may promote the resolution of inflammation in lupus and infectious diseases. These SPM-like cells are not restricted to the peritoneum and may help clear apoptotic cells from tissues such as the lung, helping to prevent chronic inflammation.

Granulocyte macrophage colony-stimulating factor receptor α expression and its targeting in antigen-induced arthritis and inflammation

Background

Blockade of granulocyte macrophage colony-stimulating factor (GM-CSF) and its receptor (GM-CSFRα) is being successfully tested in trials in rheumatoid arthritis (RA) with clinical results equivalent to those found with neutralization of the current therapeutic targets, TNF and IL-6. To explore further the role of GM-CSF as a pro-inflammatory cytokine, we examined the effect of anti-GM-CSFRα neutralization on myeloid cell populations in antigen-driven arthritis and inflammation models and also compared its effect with that of anti-TNF and anti-IL-6.

Methods

Cell population changes upon neutralization by monoclonal antibodies (mAbs) in the antigen-induced arthritis (AIA) and antigen-induced peritonitis (AIP) models were monitored by flow cytometry and microarray. Adoptive transfer of monocytes into the AIP cavity was used to assess the GM-CSF dependence of the development of macrophages and monocyte-derived dendritic cells (Mo-DCs) at a site of inflammation.

Results

Therapeutic administration of a neutralizing anti-GM-CSF mAb, but not of an anti-colony-stimulating factor (anti-CSF)-1 or an anti-CSF-1R mAb, ameliorated AIA disease. Using the anti-GM-CSFRα mAb, the relative surface expression of different inflammatory myeloid populations was found to be similar in the inflamed tissues in both the AIA and AIP models; however, the GM-CSFRα mAb, but not neutralizing anti-TNF and anti-IL-6 mAbs, preferentially depleted Mo-DCs from these sites. In addition, we were able to show that locally acting GM-CSF upregulated macrophage/Mo-DC numbers via GM-CSFR signalling in donor monocytes.

Conclusions

Our findings suggest that GM-CSF blockade modulates inflammatory responses differently to TNF and IL-6 blockade and may provide additional insight into how targeting the GM-CSF/GM-CSFRα system is providing efficacy in RA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1185-9) contains supplementary material, which is available to authorized users.

Staphylococcus aureus Induces Shedding of IL-1RII in Monocytes and Neutrophils

Interleukin 1 (IL-1) β is a critical cytokine that orchestrates host defenses against Staphylococcus aureus and is crucial for the eradication of bacteria. The production and action of IL-1β are regulated by multiple control pathways. Among them, IL-1RII (the type II IL-1 receptor) acts as a decoy receptor and has been shown to regulate the biological effects of IL-1β. High levels of soluble IL-1RII are present in septic patients; however, the stimuli that regulate the expression and release of IL-1RII in pathological conditions are incompletely elucidated. In the present study, we demonstrated the ability of S. aureus and protein A to induce IL-1RII shedding in myeloid cells. The positive modulation of IL-1RII expression and cleavage was associated with the failure to detect IL-1β in response to S. aureus both in vitro and in vivo, suggesting that the soluble form of the receptor could be masking the availability of IL-1β. The absence of detectable IL-1β was associated with low levels of inflammatory cytokines and chemokines known to be regulated by IL-1β and with increased bacterial persistence. Modulation of decoy receptors during systemic S. aureus infection is proposed as a new strategy used by this bacterium to evade the immune response.

The resolution of inflammation: Principles and challenges

The concept that chemokines, cytokines and pro-inflammatory mediators act in a co-ordinated fashion to drive the initiation of the inflammatory reaction is well understood. The significance of such networks acting during the resolution of inflammation however is poorly appreciated. In recent years, specific pro-resolving mediators were discovered which activate resolution pathways to return tissues to homeostasis. These mediators are diverse in nature, and include specialized lipid mediators (lipoxins, resolvins, protectins and maresins) proteins (annexin A1, galectins) and peptides, gaseous mediators including hydrogen sulphide, a purine (adenosine), as well as neuromodulator release under the control of the vagus nerve. Functionally, they can act to limit further leukocyte recruitment, induce neutrophil apoptosis and enhance efferocytosis by macrophages. They can also switch macrophages from classical to alternatively activated cells, promote the return of non-apoptotic cells to the lymphatics and help initiate tissue repair mechanisms and healing. Within this review we highlight the essential cellular aspects required for successful tissue resolution, briefly discuss the pro-resolution mediators that drive these processes and consider potential challenges faced by researchers in the quest to discover how inflammation resolves and why chronic inflammation persists.