TLR4 induces CCR7-dependent monocytes transmigration through the blood-brain barrier

The Emerging Role of Microglial Hv1 as a Target for Immunomodulation in Myelin Repair

In the central nervous system (CNS), the myelin sheath ensures efficient interconnection between neurons and contributes to the regulation of the proper function of neuronal networks. The maintenance of myelin and the well-organized subtle process of myelin plasticity requires cooperation among myelin-forming cells, glial cells, and neural networks. The process of cooperation is fragile, and the balance is highly susceptible to disruption by microenvironment influences. Reactive microglia play a critical and complicated role in the demyelination and remyelination process. Recent studies have shown that the voltage-gated proton channel Hv1 is selectively expressed in microglia in CNS, which regulates intracellular pH and is involved in the production of reactive oxygen species, underlying multifaceted roles in maintaining microglia function. This paper begins by examining the molecular mechanisms of demyelination and emphasizes the crucial role of the microenvironment in demyelination. It focuses specifically on the role of Hv1 in myelin repair and its therapeutic potential in CNS demyelinating diseases.

Circulating immune profile in granulomatosis with polyangiitis reveals distinct patterns related to disease activity

Granulomatosis with polyangiitis (GPA) is an autoimmune disorder characterized by recurrent relapses that can cause severe tissue damage and life-threatening organ dysfunction. Multiple immune cells and cytokines/chemokines are involved in the different stages of the disease. Immune profiling of patients may be useful for tracking disease activity, however, reliable immune signatures for GPA activity are lacking. In this study, we examined circulating immune profiles in GPA patients during active and remission disease states to identify potential immune patterns associated with disease activity. The distribution and phenotypic characteristics of major circulating immune cells, and the profiles of circulating cytokines/chemokines, were studied on cryopreserved peripheral blood mononuclear cells from GPA patients (active, n = 20; remission, n = 20) and healthy controls (n = 20) leveraging a 40-color optimized multicolor immunofluorescence panel (OMIP-69) and in serum using a 46-plex Luminex multiplex assay, respectively. Deep phenotyping uncovered a distinct composition of major circulating immune cells in active GPA and GPA in remission, with the most significant findings emerging within the monocyte compartment. Our detailed analysis revealed circulating monocyte diversity beyond the conventional monocyte subsets. We identified eight classical monocyte populations, two intermediate monocyte populations, and one non-classical monocyte population. Notably, active GPA had a higher frequency of CD45RA+CCR5+CCR6-CCR7+/lowCD127-HLA-DR+CD2- classical monocytes and a lower frequency of CD45RA-CCR5-/lowCCR6-CCR7-CD127-HLA-DR+CD2+/- classical monocytes, which both strongly correlated with disease activity. Furthermore, serum levels of CXCL1, CXCL2, and CCL20, all linked to monocyte biology, were elevated in active GPA and correlated strongly with disease activity. These findings shed light on the circulating immune profile of GPA and may lead to immune signature profiles for assessing disease activity. Monocytes in particular may be studied further as potential markers for monitoring GPA.

High-dimensional phenotyping of the peripheral immune response in community-acquired pneumonia

Background

Community-acquired pneumonia (CAP) represents a major health burden worldwide. Dysregulation of the immune response plays an important role in adverse outcomes in patients with CAP.

Methods

We analyzed peripheral blood mononuclear cells by 36-color spectral flow cytometry in adult patients hospitalized for CAP (n=40), matched control subjects (n=31), and patients hospitalized for COVID-19 (n=35).

Results

We identified 86 immune cell metaclusters, 19 of which (22.1%) were differentially abundant in patients with CAP versus matched controls. The most notable differences involved classical monocyte metaclusters, which were more abundant in CAP and displayed phenotypic alterations reminiscent of immunosuppression, increased susceptibility to apoptosis, and enhanced expression of chemokine receptors. Expression profiles on classical monocytes, driven by CCR7 and CXCR5, divided patients with CAP into two clusters with a distinct inflammatory response and disease course. The peripheral immune response in patients with CAP was highly similar to that in patients with COVID-19, but increased CCR7 expression on classical monocytes was only present in CAP.

Conclusion

CAP is associated with profound cellular changes in blood that mainly relate to classical monocytes and largely overlap with the immune response detected in COVID-19.

Monocyte subset redistribution from blood to kidneys in patients with Puumala virus caused hemorrhagic fever with renal syndrome

Innate immune cells like monocytes patrol the vasculature and mucosal surfaces, recognize pathogens, rapidly redistribute to affected tissues and cause inflammation by secretion of cytokines. We previously showed that monocytes are reduced in blood but accumulate in the airways of patients with Puumala virus (PUUV) caused hemorrhagic fever with renal syndrome (HFRS). However, the dynamics of monocyte infiltration to the kidneys during HFRS, and its impact on disease severity are currently unknown. Here, we examined longitudinal peripheral blood samples and renal biopsies from HFRS patients and performed in vitro experiments to investigate the fate of monocytes during HFRS. During the early stages of HFRS, circulating CD14-CD16+ nonclassical monocytes (NCMs) that patrol the vasculature were reduced in most patients. Instead, CD14+CD16- classical (CMs) and CD14+CD16+ intermediate monocytes (IMs) were increased in blood, in particular in HFRS patients with more severe disease. Blood monocytes from patients with acute HFRS expressed higher levels of HLA-DR, the endothelial adhesion marker CD62L and the chemokine receptors CCR7 and CCR2, as compared to convalescence, suggesting monocyte activation and migration to peripheral tissues during acute HFRS. Supporting this hypothesis, increased numbers of HLA-DR+, CD14+, CD16+ and CD68+ cells were observed in the renal tissues of acute HFRS patients compared to controls. In vitro, blood CD16+ monocytes upregulated CD62L after direct exposure to PUUV whereas CD16- monocytes upregulated CCR7 after contact with PUUV-infected endothelial cells, suggesting differential mechanisms of activation and response between monocyte subsets. Together, our findings suggest that NCMs are reduced in blood, potentially via CD62L-mediated attachment to endothelial cells and monocytes are recruited to the kidneys during HFRS. Monocyte mobilization, activation and functional impairment together may influence the severity of disease in acute PUUV-HFRS.

The Impact of Gut Microbiota Disorders on the Blood-Brain Barrier

The gut microbiota is symbiotic with the human host and has been extensively studied in recent years resulting in increasing awareness of the effects of the gut microbiota on human health. In this review, we summarize the current evidence for the effects of gut microbes on the integrity of the cerebral blood-brain barrier (BBB), focusing on the pathogenic impact of gut microbiota disorders. Based on our description and summarization of the effects of the gut microbiota and its metabolites on the nervous, endocrine, and immune systems and related signaling pathways and the resulting destruction of the BBB, we suggest that regulating and supplementing the intestinal microbiota as well as targeting immune cells and inflammatory mediators are required to protect the BBB.

Monocyte mobilisation, microbiota & mental illness

The gastrointestinal microbiome has emerged as a key player in regulating brain and behaviour. This has led to the strategy of targeting the gut microbiota to ameliorate disorders of the central nervous system. Understanding the underlying signalling pathways in which the microbiota impacts these disorders is crucial for the development of future therapeutics for improving CNS functionality. One of the major pathways through which the microbiota influences the brain is the immune system, where there is an increasing appreciation for the role of monocyte trafficking in regulating brain homeostasis. In this review, we will shed light on the role of monocyte trafficking as a relay of microbiota signals in conditions where the central nervous system is in disorder, such as stress, peripheral inflammation, ageing, traumatic brain injury, stroke, multiple sclerosis, Alzheimer's disease and Parkinson's disease. We also cover how the gastrointestinal microbiota is implicated in these mental illnesses. In addition, we aim to discuss how the monocyte system can be modulated by the gut microbiota to mitigate disorders of the central nervous system, which will lead to novel microbiota-targeted strategies.

NADPH Oxidase 1 in Liver Macrophages Promotes Inflammation and Tumor Development in Mice

BACKGROUND & AIMS

Although there are associations among oxidative stress, reduced nicotinamide adenine dinucleotide phosphate oxidase (NOX) activation, and hepatocellular carcinoma (HCC) development, it is not clear how NOX contributes to hepatocarcinogenesis. We studied the functions of different NOX proteins in mice after administration of a liver carcinogen.

METHODS

Fourteen-day-old Nox1^-/- mice, Nox4^-/- mice, Nox1^-/-Nox4^-/- (double-knockout) mice, and wild-type (WT) C57BL/6 mice were given a single intraperitoneal injection of diethylnitrosamine (DEN) and liver tumors were examined at 9 months. We also studied the effects of DEN in mice with disruption of Nox1 specifically in hepatocytes (Nox1^ΔHep), hepatic stellate cells (Nox1^ΔHep), or macrophages (Nox1^ΔMac). Some mice were also given injections of the NOX1-specific inhibitor ML171. To study the acute effects of DEN, 8-12-week-old mice were given a single intraperitoneal injection, and liver and serum were collected at 72 hours. Liver tissues were analyzed by histologic examination, quantitative polymerase chain reaction, and immunoblots. Hepatocytes and macrophages were isolated from WT and knockout mice and analyzed by immunoblots.

RESULTS

Nox4^-/- mice and WT mice developed liver tumors within 9 months after administration of DEN, whereas Nox1^-/- mice developed 80% fewer tumors, which were 50% smaller than those of WT mice. Nox1^ΔHep and Nox1^ΔHSC mice developed liver tumors of the same number and size as WT mice, whereas Nox1^ΔMac developed fewer and smaller tumors, similar to Nox1^-/- mice. After DEN injection, levels of tumor necrosis factor, interleukin 6 (IL6), and phosphorylated signal transducer and activator of transcription 3 were increased in livers from WT, but not Nox1^-/- or Nox1^ΔMac, mice. Conditioned medium from necrotic hepatocytes induced expression of NOX1 in cultured macrophages, followed by expression of tumor necrosis factor, IL6, and other inflammatory cytokines; this medium did not induce expression of IL6 or cytokines in Nox1^ΔMac macrophages. WT mice given DEN followed by ML171 developed fewer and smaller liver tumors than mice given DEN followed by vehicle.

CONCLUSIONS

In mice given injections of a liver carcinogen (DEN), expression of NOX1 by macrophages promotes hepatic tumorigenesis by inducing the production of inflammatory cytokines. We propose that upon liver injury, damage-associated molecular patterns released from dying hepatocytes activate liver macrophages to produce cytokines that promote tumor development. Strategies to block NOX1 or these cytokines might be developed to slow hepatocellular carcinoma progression.

Combined Effect of TLR2 Ligands on ROS Production by Mouse Peritoneal Macrophages

TLR2-mediated ROS production by mouse peritoneal macrophages was studied by luminoldependent chemiluminescence under conditions of cell stimulation with zymosan (TLR2/6 ligand) and peptidoglycan (TLR2/1 ligand). ROS production by macrophages stimulated with zymosan and peptidoglycan simultaneously depended on the ratio of ligand concentrations. Three effects were revealed: additivity of the stimulating effects of the ligands used, competitive ligand binding, and effect of macrophage priming with peptidoglycan during cell stimulation with zymosan. The mechanisms of these effects are discussed.

Inflammatory demyelinating diseases of the central nervous system

Inflammatory demyelinating diseases are a heterogeneous group of disorders, which occur against the background of an acute or chronic inflammatory process. The pathologic hallmark of multiple sclerosis (MS) is the presence of focal demyelinated lesions with partial axonal preservation and reactive astrogliosis. Demyelinated plaques are present in the white as well as gray matter, such as the cerebral or cerebellar cortex and brainstem nuclei. Activity of the disease process is reflected by the presence of lesions with ongoing myelin destruction. Axonal and neuronal destruction in the lesions is a major substrate for permanent neurologic deficit in MS patients. The MS pathology is qualitatively similar in different disease stages, such as relapsing remitting MS or secondary or primary progressive MS, but the prevalence of different lesion types differs quantitatively. Acute MS and Balo's type of concentric sclerosis appear to be variants of classic MS. In contrast, neuromyelitis optica (NMO) and spectrum disorders (NMOSD) are inflammatory diseases with primary injury of astrocytes, mediated by aquaporin-4 antibodies. Finally, we discuss the histopathology of other inflammatory demyelinating diseases such as acute disseminated encephalomyelitis and myelin oligodendrocyte glycoprotein antibody-associated demyelination. Knowledge of the heterogenous immunopathology in demyelinating diseases is important, to understand the clinical presentation and disease course and to find the optimal treatment for an individual patient.