Norihisa Mikami

Calcitonin Gene-Related Peptide Is an Important Regulator of Cutaneous Immunity: Effect on Dendritic Cell and T Cell Functions

Some cutaneous inflammations are induced by percutaneous exposure to foreign Ags, and many chemical mediators regulate this inflammation process. One of these mediators, calcitonin gene-related peptide (CGRP), is a neuropeptide released from nerve endings in the skin. CGRP binds to its receptors composed of receptor activity-modifying protein 1 and calcitonin receptor-like receptor to modulate immune cell function. We show that CGRP regulates skin inflammation under physiological conditions, using contact hypersensitivity (CHS) models of receptor activity-modifying protein 1–deficient mice. CGRP has different functions in CHS responses mediated by Th1 or Th2 cells; it inhibits Th1-type CHS, such as 2,4,6-trinitrochlorobenzene–induced CHS, but promotes Th2-type CHS, such as FITC-induced CHS. CGRP inhibits the migration of Langerin+ dermal dendritic cells to the lymph nodes in 2,4,6-trinitrochlorobenzene–induced CHS, and upregulates IL-4 production of T cells in the draining lymph nodes in FITC-CHS. These findings suggest that CGRP regulates several types of CHS reactions under physiological conditions and plays an important role in cutaneous immunity.

Calcitonin Gene-Related Peptide and Cyclic Adenosine 5′-Monophosphate/Protein Kinase A Pathway Promote IL-9 Production in Th9 Differentiation Process

Th9 cells are a novel Th cell subset that produces IL-9 and is involved in type I hypersensitivity such as airway inflammation. Although its critical roles in asthma have attracted interest, the physiological regulatory mechanisms of Th9 cell differentiation and function are largely unknown. Asthma is easily affected by psychological factors. Therefore, we investigated one of the physiological mediators derived from the nervous system, calcitonin gene-related peptide (CGRP), in asthma and Th9 cells because CGRP and activation of the cAMP/protein kinase A (PKA) pathway by CGRP are known to be important regulators in several immune responses and allergic diseases. In this study, we demonstrated that the CGRP/cAMP/PKA pathway promotes IL-9 production via NFATc2 activation by PKA-dependent glycogen synthase kinase-3β inactivation. Moreover, CGRP also induces the expression of PU.1, a critical transcriptional factor in Th9 cells, which depends on PKA, but not NFATc2. Additionally, we demonstrated the physiological importance of CGRP in IL-9 production and Th9 differentiation using an OVA-induced airway inflammation model and T cell–specific CGRP receptor-deficient mice. The present study revealed a novel regulatory mechanism comprising G protein–coupled receptor ligands and nervous system-derived substances in Th9 cell differentiation and type I hypersensitivity.

Calcitonin gene-related peptide enhances experimental autoimmune encephalomyelitis by promoting Th17-cell functions.

T(h)17 cells, an inflammatory T helper cell subset, are involved in the pathogenesis of various inflammatory, autoimmune and allergic diseases. Recent evidence supports the idea that immune cell functions and the inflammatory response are finely regulated by various physiological substances. Calcitonin gene-related peptide (CGRP), a neuropeptide released from the sensory nerve endings, is one of these mediators. By binding to its receptor composed of receptor activity-modifying protein 1 (RAMP1) and calcitonin receptor-like receptor, CGRP modulates various immune cell functions, but the function of CGRP in T(h)17 cells is largely unknown. Here, we investigated the effect of CGRP signaling on T(h)17 cells and T(h)17 cell-mediated inflammation and observed that CGRP activates nuclear factor of activated T cells c2 through cAMP/PKA to increase IL-17 production in vitro. In vivo, IL-17 production is suppressed in RAMP1-deficient mice in the experimental autoimmune encephalomyelitis (EAE) model and RAMP1-deficient mice are completely resistant to EAE. Furthermore, T(h)17 cell function and EAE induction are also suppressed in T cell-specific RAMP1-deficient mice. Taken together, our findings indicate that CGRP promotes T(h)17 cell-mediated autoimmune inflammation through the regulation of IL-17 expression.

Calcitonin Gene-Related Peptide Regulates Type IV Hypersensitivity through Dendritic Cell Functions

Dendritic cells (DCs) play essential roles in both innate and adaptive immune responses. In addition, mutual regulation of the nervous system and immune system is well studied. One of neuropeptides, calcitonin gene-related peptide (CGRP), is a potent regulator in immune responses; in particular, it has anti-inflammatory effects in innate immunity. For instance, a deficiency of the CGRP receptor component RAMP 1 (receptor activity-modifying protein 1) results in higher cytokine production in response to LPS (lipopolysaccharide). On the other hand, how CGRP affects DCs in adaptive immunity is largely unknown. In this study, we show that CGRP suppressed Th1 cell differentiation via inhibition of IL-12 production in DCs using an in vitro co-culture system and an in vivo ovalbumin-induced delayed-type hypersensitivity (DTH) model. CGRP also down-regulated the expressions of chemokine receptor CCR2 and its ligands CCL2 and CCL12 in DCs. Intriguingly, the frequency of migrating CCR2+ DCs in draining lymph nodes of RAMP1-deficient mice was higher after DTH immunization. Moreover, these CCR2+ DCs highly expressed IL-12 and CD80, resulting in more effective induction of Th1 differentiation compared with CCR2− DCs. These results indicate that CGRP regulates Th1 type reactions by regulating expression of cytokines, chemokines, and chemokine receptors in DCs.

Immuno-Navigator, a batch-corrected coexpression database, reveals cell type-specific gene networks in the immune system

Significance Correlation of expression between genes can offer useful hints regarding their function or underlying regulatory mechanism. Today, large amounts of expression data are publicly available, allowing researchers to estimate expression correlation over thousands of samples. However, extracting information from correlation data is not straightforward, because underlying expression data are generated by different laboratories working on different cell types and under different conditions. Here we present Immuno-Navigator, a database for correlation of expression in cells of the immune system, which addresses these issues. We present examples of ways our database can be used for generating hypotheses for further experimental analysis. We demonstrate how it recapitulates known facts in immunology and successfully predicts key regulators in naturally occurring regulatory T cells. High-throughput gene expression data are one of the primary resources for exploring complex intracellular dynamics in modern biology. The integration of large amounts of public data may allow us to examine general dynamical relationships between regulators and target genes. However, obstacles for such analyses are study-specific biases or batch effects in the original data. Here we present Immuno-Navigator, a batch-corrected gene expression and coexpression database for 24 cell types of the mouse immune system. We systematically removed batch effects from the underlying gene expression data and showed that this removal considerably improved the consistency between inferred correlations and prior knowledge. The data revealed widespread cell type-specific correlation of expression. Integrated analysis tools allow users to use this correlation of expression for the generation of hypotheses about biological networks and candidate regulators in specific cell types. We show several applications of Immuno-Navigator as examples. In one application we successfully predicted known regulators of importance in naturally occurring Treg cells from their expression correlation with a set of Treg-specific genes. For one high-scoring gene, integrin β8 (Itgb8), we confirmed an association between Itgb8 expression in forkhead box P3 (Foxp3)-positive T cells and Treg-specific epigenetic remodeling. Our results also suggest that the regulation of Treg-specific genes within Treg cells is relatively independent of Foxp3 expression, supporting recent results pointing to a Foxp3-independent component in the development of Treg cells.

CD28 signals the differential control of regulatory T cells and effector T cells

One possible means of driving antigen‐specific immune suppression is to expand or induce antigen‐specific FoxP3‐expressing Treg cells. One way of activating and expanding these specialized cells, both in vitro and in vivo, is by strong costimulation via CD28 with an agonistic anti‐CD28 monoclonal antibody, called anti‐CD28 superagonist (CD28SA). However, CD28SA also strongly activates conventional T (Tconv) cells to secrete proinflammatory cytokines and, under certain conditions, causes serious cytokine release syndrome. In this issue of European Journal of Immunology, Tabares et al. [Eur. J. Immunol. 2014. 44: 1225–1236] address how CD28SA can be used for the differential control of human Treg and Tconv cells to suppress immune responses without serious adverse effects. They show that, depending on the dose of the antibody or by comedication of cortico‐steroid, the selective expansion of Treg cells can be achieved without significantly activating Tconv cells to produce inflammatory cytokines. This difference in CD28 signal sensitivity between the two populations can be exploited for better control of immune responses.

Suppression of ovalbumin-induced allergic diarrhea by diminished intestinal peristalsis in RAMP1-deficient mice

Recent studies have revealed that various neurotransmitters regulate the immune system via their receptors expressed on the immune cells. Calcitonin gene-related peptide (CGRP), a sensory nerve C-fiber neuropeptide, is also known to have the ability to modulate the functions of immune cells in vitro. However, the contribution of CGRP to the immune regulation in vivo remains to be fully elucidated. Here we report that mice deficient in receptor activity-modifying protein 1 (RAMP1), which is a subunit of the CGRP receptor, showed a significantly lower incidence of diarrhea compared with wild-type (WT) mice in the ovalbumin (OVA)-induced food allergic model. Serum OVA-specific IgE levels and the differentiation of T helper cells was comparable in WT mice and RAMP1-deficient mice. Moreover, there were no significant differences between recruitment and degranulation of mast cells in the small intestine of these mice. In contrast, significantly diminished intestinal peristalsis was observed by the allergy induction in RAMP1-deficient mice compared with WT mice. These results suggest that this suppression of allergic diarrhea is due to the diminished intestinal peristalsis in RAMP1-deficient mice.

Combination treatment with fingolimod and a pathogenic antigen prevents relapse of glucose‐6‐phosphate isomerase peptide‐induced arthritis

Combination treatment with fingolimod (FTY720) plus pathogenic antigen is thought to prevent glucose‐6‐phosphate isomerase (GPI)325‐339‐induced arthritis progression by effective induction of immune tolerance. Here, we examined the efficacy of this combination treatment on remission maintenance.

Lamtor1 Is Critically Required for CD4+ T Cell Proliferation and Regulatory T Cell Suppressive Function

Mechanistic target of rapamycin complex (mTORC)1 integrates intracellular sufficiency of nutrients and regulates various cellular functions. Previous studies using mice with conditional knockout of mTORC1 component proteins (i.e., mTOR, Raptor, and Rheb) gave conflicting results on the roles of mTORC1 in CD4+ T cells. Lamtor1 is the protein that is required for amino acid sensing and activation of mTORC1; however, the roles of Lamtor1 in T cells have not been investigated. In this article, we show that Lamtor1-deficient CD4+ T cells exhibited marked reductions in proliferation, IL-2 production, mTORC1 activity, and expression of purine- and lipid-synthesis genes. Polarization of Th17 cells, but not Th1 and Th2 cells, diminished following the loss of Lamtor1. Accordingly, CD4-Cre–driven Lamtor1-knockout mice exhibited reduced numbers of CD4+ and CD8+ T cells at rest, and they were completely resistant to experimental autoimmune encephalomyelitis. In contrast, genetic ablation of Lamtor1 in Foxp3+ T cells resulted in severe autoimmunity and premature death. Lamtor1-deficient regulatory T cells survived ex vivo as long as wild-type regulatory T cells; however, they exhibited a marked loss of suppressive function and expression of signature molecules, such as CTLA-4. These results indicate that Lamtor1 plays essential roles in CD4+ T cells. Our data suggest that Lamtor1 should be considered a novel therapeutic target in immune systems.

Mechanism of induction of immune tolerance in experimental autoimmune encephalomyelitis by combination treatment with fingolimod plus pathogenic autoantigen

We previously reported that relapse of experimental autoimmune encephalomyelitis (EAE) occurred approximately 1 week after discontinuation of fingolimod (FTY720), but combination treatment with FTY720 plus pathogenic autoantigen significantly suppressed occurrence of relapse. Here, we investigated the mechanism of this suppression.