Bone marrow chimeras-a vital tool in basic and translational research

Innervation of nociceptor neurons in the spleen promotes germinal center responses and humoral immunity

Peripheral sensory neurons widely innervate various tissues to continuously monitor and respond to environmental stimuli. Whether peripheral sensory neurons innervate the spleen and modulate splenic immune response remains poorly defined. Here, we demonstrate that nociceptive sensory nerve fibers extensively innervate the spleen along blood vessels and reach B cell zones. The spleen-innervating nociceptors predominantly originate from left T8-T13 dorsal root ganglia (DRGs), promoting the splenic germinal center (GC) response and humoral immunity. Nociceptors can be activated by antigen-induced accumulation of splenic prostaglandin E2 (PGE2) and then release calcitonin gene-related peptide (CGRP), which further promotes the splenic GC response at the early stage. Mechanistically, CGRP directly acts on B cells through its receptor CALCRL-RAMP1 via the cyclic AMP (cAMP) signaling pathway. Activating nociceptors by ingesting capsaicin enhances the splenic GC response and anti-influenza immunity. Collectively, our study establishes a specific DRG-spleen sensory neural connection that promotes humoral immunity, suggesting a promising approach for improving host defense by targeting the nociceptive nervous system.

Long-term hematopoietic transfer of the anti-cancer and lifespan-extending capabilities of a genetically engineered blood system by transplantation of bone marrow mononuclear cells

A causal relationship exists among the aging process, organ decay and disfunction, and the occurrence of various diseases including cancer. A genetically engineered mouse model, termed Klf1K74R/K74R or Klf1(K74R), carrying mutation on the well-conserved sumoylation site of the hematopoietic transcription factor KLF1/EKLF has been generated that possesses extended lifespan and healthy characteristics, including cancer resistance. We show that the healthy longevity characteristics of the Klf1(K74R) mice, as exemplified by their higher anti-cancer capability, are likely gender-, age-, and genetic background-independent. Significantly, the anti-cancer capability, in particular that against melanoma as well as hepatocellular carcinoma, and lifespan-extending property of Klf1(K74R) mice, could be transferred to wild-type mice via transplantation of their bone marrow mononuclear cells at a young age of the latter. Furthermore, NK(K74R) cells carry higher in vitro cancer cell-killing ability than wild-type NK cells. Targeted/global gene expression profiling analysis has identified changes in the expression of specific proteins, including the immune checkpoint factors PDCD and CD274, and cellular pathways in the leukocytes of the Klf1(K74R) that are in the directions of anti-cancer and/or anti-aging. This study demonstrates the feasibility of developing a transferable hematopoietic/blood system for long-term anti-cancer and, potentially, for anti-aging.

IKKβ deletion from CNS macrophages increases neuronal excitability and accelerates the onset of EAE, while from peripheral macrophages reduces disease severity

BACKGROUND

Multiple sclerosis (MS) is a neuroinflammatory demyelinating disease characterized by motor deficits and cognitive decline. Many immune aspects of the disease are understood through studies in the experimental autoimmune encephalomyelitis (EAE) model, including the contribution of the NF-κB transcription factor to neuroinflammation. However, the cell-specific roles of NF-κB to EAE and its cognitive comorbidities still needs further investigation. We have previously shown that the myeloid cell NF-κB plays a role in the healthy brain by exerting homeostatic regulation of neuronal excitability and synaptic plasticity and here we investigated its role in EAE.

METHODS

We used constitutive MφIKKβΚΟ mice, in which depletion of IKKβ, the main activating kinase of NF-κB, was global to CNS and peripheral macrophages, and ΜgΙΚΚβKO mice, in which depletion was inducible and specific to CNS macrophages by 28 days after tamoxifen administration. We subjected these mice to MOG35-55 induced EAE and cuprizone-induced demyelination. We measured pathology by immunohistochemistry, investigated molecular mechanisms by RNA sequencing analysis and studied neuronal functions by in vivo electrophysiology in awake animals.

RESULTS

Global depletion of IKKβ from myeloid cells in MφIKKβΚΟ mice accelerated the onset and significantly supressed chronic EAE. Knocking out IKKβ only from CNS resident macrophages accelerated the onset and exacerbated chronic EAE, accompanied by earlier demyelination and immune cell infiltration but had no effect in cuprizone-induced demyelination. Peripheral T cell effector functions were not affected by myeloid cell deletion of IKKβ, but CNS resident mechanisms, such as microglial activation and neuronal hyperexcitability were altered from early in EAE. Lastly, depletion of myeloid cell IKKβ resulted in enhanced late long-term potentiation in EAE.

CONCLUSIONS

IKKβ-mediated activation of NF-κΒ in myeloid cells has opposing roles in EAE depending on the cell type and the disease stage. In CNS macrophages it is protective while in peripheral macrophages it is disease-promoting and acts mainly during chronic disease. Although clinically protective, CNS myeloid cell IKKβ deletion dysregulates neuronal excitability and synaptic plasticity in EAE. These effects of IKKβ on brain cognitive abilities deserve special consideration when therapeutic interventions that inhibit NF-κB are used in MS.

Generation of Bone Marrow Chimeras

Bone marrow chimeras are widely used in immunological studies, to dissect the contributions of hematopoietic and non-hematopoietic cells in immune cell development or functions, to quantify the impact of a given mutation, or in preclinical studies for hematopoietic stem cell transplantation. Here we describe a set of procedures for the generation of bone marrow chimeras.

Extrahepatic factors in hepatic immune regulation

The liver is a site of complex immune activity. The hepatic immune system tolerates harmless immunogenic loads in homeostasis status, shelters liver function, while maintaining vigilance against possible infectious agents or tissue damage and providing immune surveillance at the same time. Activation of the hepatic immunity is initiated by a diverse repertoire of hepatic resident immune cells as well as non-hematopoietic cells, which can sense "danger signals" and trigger robust immune response. Factors that mediate the regulation of hepatic immunity are elicited not only in liver, but also in other organs, given the dual blood supply of the liver via both portal vein blood and arterial blood. Emerging evidence indicates that inter-organ crosstalk between the liver and other organs such as spleen, gut, lung, adipose tissue, and brain is involved in the pathogenesis of liver diseases. In this review, we present the features of hepatic immune regulation, with particular attention to the correlation with factors from extrahepatic organ. We describe the mechanisms by which other organs establish an immune association with the liver and then modulate the hepatic immune response. We discuss their roles and distinct mechanisms in liver homeostasis and pathological conditions from the cellular and molecular perspective, highlighting their potential for liver disease intervention. Moreover, we review the available animal models and methods for revealing the regulatory mechanisms of these extrahepatic factors. With the increasing understanding of the mechanisms by which extrahepatic factors regulate liver immunity, we believe that this will provide promising targets for liver disease therapy.

Fra-2 Is a Dominant Negative Regulator of Natural Killer Cell Development

Natural killer (NK) cells play an important role in recognizing and killing pathogen-infected or malignant cells. Changes in their numbers or activation can contribute to several diseases and pathologies including systemic sclerosis (SSc), an autoimmune disease characterized by inflammation and tissue remodeling. In these patients, increased expression of the AP-1 transcription factor, Fra-2 was reported. In mice ectopic overexpression of Fra-2 (TG) leads to SSc with strong pulmonary fibrosis, pulmonary hypertension, and inflammation. Analysis of the underlying immune cell profile in the lungs of young TG mice, which do not yet show any signs of lung disease, revealed increased numbers of eosinophils and T cells but strongly reduced NK numbers. Therefore, we aimed to identify the cause of the absence of NK cells in the lungs of these mice and to determine the potential role of Fra-2 in NK development. Examination of inflammatory cell distribution in TG mice revealed similar NK deficiencies in the spleen, blood, and bone marrow. Deeper analysis of the WT and TG bone marrow revealed a potential NK cell developmental defect beginning at the preNKP stage. To determine whether this defect was cell-intrinsic or extrinsic, mixed bone marrow chimera and in vitro differentiation experiments were performed. Both experiments showed that the defect caused by Fra-2 was primarily cell-intrinsic and minimally dependent on the environment. Closer examination of surface markers and transcription factors required for NK development, revealed the expected receptor distribution but changes in transcription factor expression. We found a significant reduction in Nfil3, which is essential for the transition of common lymphoid cells to NK committed precursor cells and an AP-1 binding site in the promotor of this gene. In Summary, our data demonstrates that regulation of Fra-2 is essential for NK development and maturation, and suggests that the early NK dysfunction plays an important role in the pathogenesis of systemic sclerosis.

A cardioimmunologist's toolkit: genetic tools to dissect immune cells in cardiac disease

Cardioimmunology is a field that encompasses the immune cells and pathways that modulate cardiac function in homeostasis and regulate the temporal balance between tissue injury and repair in disease. Over the past two decades, genetic fate mapping and high-dimensional sequencing techniques have defined increasing functional heterogeneity of innate and adaptive immune cell populations in the heart and other organs, revealing a complexity not previously appreciated and challenging established frameworks for the immune system. Given these rapid advances, understanding how to use these tools has become crucial. However, cardiovascular biologists without immunological expertise might not be aware of the strengths and caveats of immune-related tools and how they can be applied to examine the pathogenesis of myocardial diseases. In this Review, we guide readers through case-based examples to demonstrate how tool selection can affect data quality and interpretation and we provide critical analysis of the experimental tools that are currently available, focusing on their use in models of ischaemic heart injury and heart failure. The goal is to increase the use of relevant immunological tools and strategies among cardiovascular researchers to improve the precision, translatability and consistency of future studies of immune cells in cardiac disease.

Myeloid-cell-specific deletion of inducible nitric oxide synthase protects against smoke-induced pulmonary hypertension in mice

BACKGROUND

Pulmonary hypertension (PH) is a common complication of COPD, associated with increased mortality and morbidity. Intriguingly, pulmonary vascular alterations have been suggested to drive emphysema development. Previously, we identified inducible nitric oxide synthase (iNOS) as an essential enzyme for development and reversal of smoke-induced PH and emphysema, and showed that iNOS expression in bone-marrow-derived cells drives pulmonary vascular remodelling, but not parenchymal destruction. In this study, we aimed to identify the iNOS-expressing cell type driving smoke-induced PH and to decipher pro-proliferative pathways involved.

METHODS

To address this question we used 1) myeloid-cell-specific iNOS knockout mice in chronic smoke exposure and 2) co-cultures of macrophages and pulmonary artery smooth muscle cells (PASMCs) to decipher underlying signalling pathways.

RESULTS

Myeloid-cell-specific iNOS knockout prevented smoke-induced PH but not emphysema in mice. Moreover, iNOS deletion in myeloid cells ameliorated the increase in expression of CD206, a marker of M2 polarisation, on interstitial macrophages. Importantly, the observed effects on lung macrophages were hypoxia-independent, as these mice developed hypoxia-induced PH. In vitro, smoke-induced PASMC proliferation in co-cultures with M2-polarised macrophages could be abolished by iNOS deletion in phagocytic cells, as well as by extracellular signal-regulated kinase inhibition in PASMCs. Crucially, CD206-positive and iNOS-positive macrophages accumulated in proximity of remodelled vessels in the lungs of COPD patients, as shown by immunohistochemistry.

CONCLUSION

In summary, our results demonstrate that iNOS deletion in myeloid cells confers protection against PH in smoke-exposed mice and provide evidence for an iNOS-dependent communication between M2-like macrophages and PASMCs in underlying pulmonary vascular remodelling.

Apolipoprotein E derived from CD11c+ cells ameliorates atherosclerosis

Atherosclerosis is studied in models with dysfunctional lipid homeostasis—predominantly the ApoE^−/− mouse. The role of antigen-presenting cells (APCs) for lipid homeostasis is not clear. Using a LacZ reporter mouse, we showed that CD11c⁺ cells were enriched in aortae of ApoE^−/− mice. Systemic long-term depletion of CD11c⁺ cells in ApoE^−/− mice resulted in significantly increased plaque formation associated with reduced serum ApoE levels. In CD11c^cre+ApoE^fl/fl and Albumin^cre+ApoE^fl/fl mice, we could show that ≈70% of ApoE is liver-derived and ≈25% originates from CD11c⁺ cells associated with significantly increased atherosclerotic plaque burden in both strains. Exposure to acLDL promoted cholesterol efflux from CD11c⁺ cells and cell-specific deletion of ApoE resulted in increased inflammation reflected by increased IL-1β serum levels. Our results determined for the first time the level of ApoE originating from CD11c⁺ cells and demonstrated that CD11c⁺ cells ameliorate atherosclerosis by the secretion of ApoE.

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CD11c⁺ cells are enriched in aortae of high cholesterol-fed ApoE^−/- mice

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Depletion of CD11c⁺ cells increases plaque size in ApoE^−/- mice

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≈ 20% of serum ApoE derives from CD11c⁺ cells

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ApoE from CD11c⁺ cells contributes to protection from atherosclerosis

Imaging of Bone Marrow Plasma Cells and of Their Niches

Decade-long survival of plasma cells in the bone marrow has long been a puzzling matter. To understand how plasma cells are maintained and supported by survival-niches to account for lifelong antibody production demands new intravital imaging techniques that are able to follow up a single cell and their interaction with other cell types in situ. We achieved to successfully establish longitudinal imaging of the bone marrow (LIMB) that is based on an implantable endoscopic device. In this chapter, basic approaches on how to investigate plasma cell-stroma interaction and surgical implantation procedures are introduced.