CCR9 axis inhibition enhances hepatic migration of plasmacytoid DCs and protects against liver injury.

Plasmacytoid dendritic cells (pDCs) perform dual proinflammatory and immunosuppressive roles. We recently reported the potential of pDC therapy for treatment of intractable acute liver failure. However, establishment of efficient methods to deliver pDCs to the liver is essential for future clinical therapeutic applications. The present study demonstrates a higher abundance of liver and peripheral blood pDCs in mice lacking C-C motif chemokine receptor 9 (CCR9), a pDC gut-homing receptor, than in WT mice. Adoptive transfer of Ccr9-/- pDCs resulted in a higher efficiency of migration to the liver than WT pDCs did, while WT pDCs migrated efficiently to the original target organ, the small intestine. Further, Ccr9-/- pDCs consistently migrated efficiently to livers with concanavalin A-induced inflammation, and exerted a more effective immunosuppressive effect, resulting in better protection against acute liver inflammation than that demonstrated by WT pDCs. These findings highlight the therapeutic potential of the manipulation of the CCR9 axis as an approach to improve migration of immunosuppressive pDCs to the liver in order to exploit their beneficial effects in acute liver disease.

Host-microbe cross-talk governs amino acid chirality to regulate survival and differentiation of B cells.

Organisms use l-amino acids (l-aa) for most physiological processes. Unlike other organisms, bacteria chiral-convert l-aa to d-configurations as essential components of their cell walls and as signaling molecules in their ecosystems. Mammals recognize microbe-associated molecules to initiate immune responses, but roles of bacterial d-amino acids (d-aa) in mammalian immune systems remain largely unknown. Here, we report that amino acid chirality balanced by bacteria-mammal cross-talk modulates intestinal B cell fate and immunoglobulin A (IgA) production. Bacterial d-aa stimulate M1 macrophages and promote survival of intestinal naïve B cells. Mammalian intestinal d-aa catabolism limits the number of B cells and restricts growth of symbiotic bacteria that activate T cell-dependent IgA class switching of the B cells. Loss of d-aa catabolism results in excessive IgA production and dysbiosis with altered IgA coating on bacteria. Thus, chiral conversion of amino acids is linked to bacterial recognition by mammals to control symbiosis with bacteria.

ß-(1,3)-Glucan derived from Candida albicans induces inflammatory cytokines from macrophages and lamina propria mononuclear cells derived from patients with Crohn's disease.

BACKGROUND/AIMS: Recent research has highlighted the importance of interactions between commensal fungi and intestinal inflammation. However, there are few studies investigating whether commensal fungi contribute to inflammation in patients with Crohn's disease (CD). The aim of this study is to investigate reveal interactions between commensal fungi and host immune cells in CD. METHODS: CD14-positive monocytes were isolated from peripheral blood mononuclear cells from healthy human volunteers and then differentiated in the presence of macrophage colony-stimulating factor (M-CSF) (referred to as M-macrophages, M-Mϕs) or M-CSF and interferon-γ (IFN-γ) (referred to as M-gamma macrophages, Mγ-Mϕs). Cytokine production by these in vitro differentiated macrophages in response to ß-(1,3)-glucan was analyzed by flow cytometry. Expression of Dectin-1 was examined using flow cytometry, western blotting, and quantitative reverse transcription-polymerase chain reaction. Cytokine production by in vitro differentiated macrophages in response to ß-(1,3)-glucan was measured in the presence of an anti-Dectin-1 receptor antagonist, anti-Syr, or an anti-Fas-1 antibody. Cytokine production by lamina propria mononuclear cells (LPMCs) derived from CD patients in response to ß-(1,3)-glucan was also analyzed. RESULTS: Mγ-Mϕs produced a large amount of tumor necrosis factor-α (TNF-α) and interleukin-6 in response to ß-(1,3)-glucan. Dectin-1 expression was significantly higher in Mγ-Mϕs than in M-Mϕs. The increase in TNF-α production by Mγ-Mϕs stimulated with glucan was reversed by blocking Dectin-1, Syr or Fas-1. LPMCs derived from CD patients stimulated with ß-(1,3)-glucan produced significantly higher amount of TNF-α than LPMCs derived from UC patients. CONCLUSIONS: These results suggest that commensal fungal microbiota may contribute to the pathogenesis of CD by inducing macrophages-derived pro-inflammatory cytokines.

Commensal Lactobacillus Controls Immune Tolerance during Acute Liver Injury in Mice.

Gut-derived microbial antigens trigger the innate immune system during acute liver injury. During recovery, regulatory immunity plays a role in suppressing inflammation; however, the precise mechanism underlying this process remains obscure. Here, we find that recruitment of immune-regulatory classical dendritic cells (cDCs) is crucial for liver tolerance in concanavalin A-induced acute liver injury. Acute liver injury resulted in enrichment of commensal Lactobacillus in the gut. Notably, Lactobacillus activated IL-22 production by gut innate lymphoid cells and raised systemic IL-22 levels. Gut-derived IL-22 enhanced mucosal barrier function and promoted the recruitment of regulatory cDCs to the liver. These cDCs produced IL-10 and TGF-ß through TLR9 activation, preventing further liver inflammation. Collectively, our results indicate that beneficial gut microbes influence tolerogenic immune responses in the liver. Therefore, modulation of the gut microbiota might be a potential option to regulate liver tolerance.

Glycolysis regulates LPS-induced cytokine production in M2 polarized human macrophages.

M1 and M2 macrophages are the key players in innate immunity, and are associated with tissue homeostasis and diseases. Although M2 macrophages are known to depend on fatty acid oxidation (FAO) for their activation, how metabolic pathways affect the production of each cytokine induced by pathogen or bacterial components is unclear. Here, we examined the role of the glycolytic pathway in M2 polarized human macrophages in cytokine production induced by lipopolysaccharide (LPS) stimulation. Human monocytes were isolated from peripheral blood by positive selection for CD14 expression and cultured with macrophage colony-stimulating factor (M-CSF), to obtain M-CSF-induced macrophages (M-MΦ). LPS-induced cytokine production by M-MΦ in the presence or absence of metabolic inhibitors was evaluated. M-MΦ showed a M2 macrophage phenotype with a high IL-10 production level. Glycolytic pathway inhibitors reduced IL-6 production by M-MΦ. Meanwhile, an FAO inhibitor suppressed IL-10 production, while it did not suppress IL-6 production. Interestingly, glycolytic pathway inhibitors downregulated extracellular signal-regulated kinase (ERK) phosphorylation, but FAO inhibitor did not. Nuclear factor kappa B (NF-κB) and the other mitogen-activated protein kinases (MAPKs), p38 and c-jun N-terminal kinase (JNK), were not affected by these metabolic inhibitors. These results suggest that M2 polarized human macrophages use the glycolytic pathway in addition to FAO for cytokine production. Furthermore, ERK may be the key molecule that links metabolic pathways to cytokine production, especially the glycolytic pathway.

Glycolytic pathway affects differentiation of human monocytes to regulatory macrophages.

Cellular metabolic state and individual metabolites have been reported to regulate the functional phenotype of immune cells. Cytokine production by regulatory and inflammatory macrophages is thought to mainly involve fatty acid oxidation and glycolysis, respectively, which fuel mitochondrial oxidative phosphorylation. However, the association between metabolic pathways and the acquisition of specific macrophage phenotypes remains unclear. This study assessed the relationship between glycolysis and the differentiation of regulatory macrophages. Human monocytes derived from peripheral blood were cultured in vitro in the presence of macrophage colony-stimulating factor to yield regulatory macrophages (M-Mϕs). M-Mϕs had a regulatory macrophage phenotype and produced substantial IL-10 following stimulation with lipopolysaccharide. To analyze the role of glycolysis, glycolysis inhibitors (2-deoxy-d-glucose or dichloroacetate) were added during M-Mϕ differentiation. These cells cultured with glycolysis inhibitors produced significantly lower amounts of IL-10, but produced significantly higher amounts of IL-6 compared to M-Mϕs differentiated without glycolysis inhibitors. Such phenotypic change of M-Mϕs differentiated with glycolysis inhibitors was associated with the alteration of the gene expression pattern related to macrophage differentiation, such as CSF1, MMP9 and VEGFA. M-Mϕs differentiated with glycolysis inhibitors seemed to retain plasticity to become IL-10 producing cells. Furthermore, increased level of pyruvate in culture medium was found to partially reverse the effects of glycolysis inhibitors on cytokine production of M-Mϕs. These results indicate the importance of glycolytic pathway in macrophage differentiation to a regulatory phenotype, and pyruvate may be one of the key metabolites in this process.