The Toll-like receptor 2 is recruited to macrophage phagosomes and discriminates between pathogens

TLR2 immunotherapy suppresses neuroinflammation, tau spread, and memory loss in rTg4510 mice

In Alzheimer's disease, chronic neuroinflammation is accompanied by amyloid and tau pathologies. Especially, aberrant microglial activation is known to precede the regional tau pathology development, but the mechanisms how microglia affect tau spread remain largely unknown. Here, we found that toll-like receptor 2 (TLR2) in microglia recognizes oligomeric tau as a pathogenic ligand and induces inflammatory responses. Knockout of TLR2 reduced tau pathology and microglial activation in rTg4510 tau transgenic mice. Treatment of oligomeric tau induced TLR2 activation and increased inflammatory responses in microglial cells. TLR2 further mediated the tau-induced microglial activation and promoted tau uptake into neurons in neuron-microglia co-culture system and in mouse hippocampus after intracranial tau injection. Importantly, treatment with anti-TLR2 monoclonal antibody Tomaralimab blocked TLR2 activation and inflammatory responses in a dose-dependent manner, and significantly reduced tau spread and memory loss in rTg4510 mice. These results suggest that TLR2 plays a crucial role in tau spread by causing aberrant microglial activation in response to pathological tau, and blocking TLR2 with immunotherapy may ameliorate tau pathogenesis in Alzheimer's disease.

Phagocytosis of microparticles increases responsiveness of macrophage-like cell lines U937 and THP-1 to bacterial lipopolysaccharide and lipopeptide

Following bacterial infection, macrophages produce pro-inflammatory cytokines in response to bacterial cell components, including lipopolysaccharide (LPS) and lipopeptide, and simultaneously phagocytize and digest the invading bacteria. To study the effects of phagocytosis on pro-inflammatory responses, we determined if phagocytosis of polystyrene latex beads with ~ 1 µm diameter increases pro-inflammatory cytokine expression by human macrophage-like U937 and THP-1 cells stimulated with LPS. Treating macrophage-like cells with beads coated with IgG to facilitate Fcγ receptor-mediated phagocytosis increased LPS-induced expression of pro-inflammatory cytokines, including tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6. Treatment with beads coated with poly-L-lysine to facilitate Fcγ receptor-independent phagocytosis also increased LPS-induced cytokine expression. Our results indicate that LPS-induced pro-inflammatory responses are enhanced by bead phagocytosis regardless of the uptake mechanism. Additionally, phagocytosis enhanced LPS-induced NF-κB activation, suggesting that Toll-like receptor (TLR) 4 signaling is enhanced by phagocytosis. Furthermore, bead phagocytosis enhanced pro-inflammatory responses in U937 cells stimulated with lipopeptide, a ligand for the TLR2/TLR6 heterodimeric receptor. In conclusion, microparticle phagocytosis by macrophage-like U937 and THP-1 cells enhances the innate immune response induced by bacterial components.

TLR2 and endosomal TLR-mediated secretion of IL-10 and immune suppression in response to phagosome-confined Listeria monocytogenes

Listeria monocytogenes is a facultative intracellular bacterial pathogen that escapes from phagosomes and induces a robust adaptive immune response in mice, while mutants unable to escape phagosomes fail to induce a robust adaptive immune response and suppress the immunity to wildtype bacteria when co-administered. The capacity to suppress immunity can be reversed by blocking IL-10. In this study, we sought to understand the host receptors that lead to secretion of IL-10 in response to phagosome-confined L. monocytogenes (Δhly), with the ultimate goal of generating strains that fail to induce IL-10. We conducted a transposon screen to identify Δhly L. monocytogenes mutants that induced significantly more or less IL-10 secretion in bone marrow-derived macrophages (BMMs). A transposon insertion in lgt, which encodes phosphatidylglycerol-prolipoprotein diacylglyceryl transferase and is essential for the formation of lipoproteins, induced significantly reduced IL-10 secretion. Mutants with transposon insertions in pgdA and oatA, which encode peptidoglycan N-acetylglucosamine deacetylase and O-acetyltransferase, are sensitive to lysozyme and induced enhanced IL-10 secretion. A ΔhlyΔpgdAΔoatA strain was killed in BMMs and induced enhanced IL-10 secretion that was dependent on Unc93b1, a trafficking molecule required for signaling of nucleic acid-sensing TLRs. These data revealed that nucleic acids released by bacteriolysis triggered endosomal TLR-mediated IL-10 secretion. Secretion of IL-10 in response to infection with the parental strain was mostly TLR2-dependent, while IL-10 secretion in response to lysozyme-sensitive strains was dependent on TLR2 and Unc93b1. In mice, the IL-10 response to vacuole-confined L. monocytogenes was also dependent on TLR2 and Unc93b1. Co-administration of Δhly and ΔactA resulted in suppressed immunity in WT mice, but not in mice with mutations in Unc93b1. These data revealed that secretion of IL-10 in response to L. monocytogenes infection in vitro is mostly TLR2-dependent and immune suppression by phagosome-confined bacteria in vivo is mostly dependent on endosomal TLRs.

Enteric Virome Sensing-Its Role in Intestinal Homeostasis and Immunity

Pattern recognition receptors (PRRs) sensing commensal microorganisms in the intestine induce tightly controlled tonic signaling in the intestinal mucosa, which is required to maintain intestinal barrier integrity and immune homeostasis. At the same time, PRR signaling pathways rapidly trigger the innate immune defense against invasive pathogens in the intestine. Intestinal epithelial cells and mononuclear phagocytes in the intestine and the gut-associated lymphoid tissues are critically involved in sensing components of the microbiome and regulating immune responses in the intestine to sustain immune tolerance against harmless antigens and to prevent inflammation. These processes have been mostly investigated in the context of the bacterial components of the microbiome so far. The impact of viruses residing in the intestine and the virus sensors, which are activated by these enteric viruses, on intestinal homeostasis and inflammation is just beginning to be unraveled. In this review, we will summarize recent findings indicating an important role of the enteric virome for intestinal homeostasis as well as pathology when the immune system fails to control the enteric virome. We will provide an overview of the virus sensors and signaling pathways, operative in the intestine and the mononuclear phagocyte subsets, which can sense viruses and shape the intestinal immune response. We will discuss how these might interact with resident enteric viruses directly or in context with the bacterial microbiome to affect intestinal homeostasis.

Mecp2 regulates tnfa during zebrafish embryonic development and acute inflammation

Mutations in MECP2 cause Rett syndrome, a severe neurological disorder with autism-like features. Duplication of MECP2 also causes severe neuropathology. Both diseases display immunological abnormalities that suggest a role for MECP2 in controlling immune and inflammatory responses. Here, we used mecp2-null zebrafish to study the potential function of Mecp2 as an immunological regulator. Mecp2 deficiency resulted in an increase in neutrophil infiltration and upregulated expression of the pro- and anti-inflammatory cytokines Il1b and Il10 as a secondary response to disturbances in tissue homeostasis. By contrast, expression of the proinflammatory cytokine tumor necrosis factor alpha (Tnfa) was consistently downregulated in mecp2-null animals during development, representing the earliest developmental phenotype described for MECP2 deficiency to date. Expression of tnfa was unresponsive to inflammatory stimulation, and was partially restored by re-expression of functional mecp2 Thus, Mecp2 is required for tnfa expression during zebrafish development and inflammation. Finally, RNA sequencing of mecp2-null embryos revealed dysregulated processes predictive for Rett syndrome phenotypes.

Microglia and Monocytes/Macrophages Polarization Reveal Novel Therapeutic Mechanism against Stroke

Stroke is a leading cause of morbidity and mortality worldwide, and consists of two types, ischemic and hemorrhagic. Currently, there is no effective treatment to increase the survival rate or improve the quality of life after ischemic and hemorrhagic stroke in the subacute to chronic phases. Therefore, it is necessary to establish therapeutic strategies to facilitate functional recovery in patients with stroke during both phases. Cell-based therapies, using microglia and monocytes/macrophages preconditioned by optimal stimuli and/or any therapies targeting these cells, might be an ideal therapeutic strategy for managing stroke. Microglia and monocytes/macrophages polarize to the classic pro-inflammatory type (M1-like) or alternative protective type (M2-like) by optimal condition. Cell-based therapies using M2-like microglia and monocytes/macrophages might be protective therapeutic strategies against stroke for three reasons. First, M2-like microglia and monocytes/monocytes secrete protective remodeling factors, thus prompting neuronal network recovery via tissue (including neuronal) and vascular remodeling. Second, these cells could migrate to the injured hemisphere through the blood–brain barrier or choroid–plexus. Third, these cells could mitigate the extent of inflammation-induced injuries by suitable timing of therapeutic intervention. Although future translational studies are required, M2-like microglia and monocytes/macrophages therapies are attractive for managing stroke based on their protective functions.

Response of the rainbow trout monocyte/macrophage cell line, RTS11 to the water molds Achlya and Saprolegnia

The Saprolegniales are responsible for various fish mycoses worldwide and considered the most important fungi afflicting fresh water fish. Saprolegniosis leads to massive epidermal destruction and macrophage recruitment, yet little is known regarding the cytological response of their piscine hosts. The objective of this study was to explore the response of fish macrophage to members of the Saprolegniales using the rainbow trout monocyte/macrophage cell line, RTS11. After 48 h in co-culture, RTS11 demonstrated chemotaxis, adherence and homotypic aggregation to both live and heat-killed fungal spores and mycelia. This aggregation was enhanced when using conditioned media from co-cultured RTS11 and Achlya, suggesting the presence of synergistic effectors of aggregation. Although fungal toxins were not evident, as cells remained viable throughout fungal overgrowth, phagocytosis was inhibited due to large fungal spore size, allowing these molds to evade macrophage defenses. Although class I MH and other viral response genes showed no significant change in expression, calreticulin and interleukin-8 were moderately up-regulated implicating calcium modulation and chemotactic response, respectively. Cyclooxygenase (COX-2) and the cytokines IL-1beta and TNFalpha were strongly up-regulated in the presence of Achlya, while gene expression of the class II major histocompatibility (MH II) receptor and associated molecules appeared down-regulated, suggesting fungal interference of immune function. Previous studies have shown an increased dependence of macrophage in immune function at low temperatures; based upon data presented here, this reduction of macrophage MH II receptor expression and inability to phagocytose spores may limit host response thereby providing increased susceptibility to these opportunistic pathogens.