Maryse Brait

Mouse ChemR23 Is Expressed in Dendritic Cell Subsets and Macrophages, and Mediates an Anti-Inflammatory Activity of Chemerin in a Lung Disease Model

Chemerin is the ligand of the ChemR23 receptor and a chemoattractant factor for human immature dendritic cells (DCs), macrophages, and NK cells. In this study, we characterized the mouse chemerin/ChemR23 system in terms of pharmacology, structure-function, distribution, and in vivo biological properties. Mouse chemerin is synthesized as an inactive precursor (prochemerin) requiring, as in human, the precise processing of its C terminus for generating an agonist of ChemR23. Mouse ChemR23 is highly expressed in immature plasmacytoid DCs and at lower levels in myeloid DCs, macrophages, and NK cells. Mouse prochemerin is expressed in most epithelial cells acting as barriers for pathogens but not in leukocytes. Chemerin promotes calcium mobilization and chemotaxis on DCs and macrophages and these functional responses were abrogated in ChemR23 knockout mice. In a mouse model of acute lung inflammation induced by LPS, chemerin displayed potent anti-inflammatory properties, reducing neutrophil infiltration and inflammatory cytokine release in a ChemR23-dependent manner. ChemR23 knockout mice were unresponsive to chemerin and displayed an increased neutrophil infiltrate following LPS challenge. Altogether, the mouse chemerin/ChemR23 system is structurally and functionally conserved between human and mouse, and mouse can therefore be considered as a good model for studying the anti-inflammatory role of this system in the regulation of immune responses and inflammatory diseases.

TLR4 and Toll-IL-1 Receptor Domain-Containing Adapter-Inducing IFN-β, but Not MyD88, Regulate Escherichia coli-Induced Dendritic Cell Maturation and Apoptosis In Vivo

Dendritic cells (DC) are short-lived, professional APCs that play a central role in the generation of adaptive immune responses. Induction of efficient immune responses is dependent on how long DCs survive in the host. Therefore, the regulation of DC apoptosis in vivo during infection remains an important question that requires further investigation. The impact of Escherichia coli bacteremia on DCs has never been analyzed. We show here that i.v. or i.p. administration of live or heat-killed E. coli in mice induces splenic DC migration, maturation, and apoptosis. We further characterize which TLR and Toll-IL-1R (TIR)-containing adaptor molecules regulate these processes in vivo. In this model, DC maturation is impaired in TLR2−/−, TLR4−/− and TIR domain-containing adapter-inducing IFN-β (TRIF)−/− mice. In contrast, DC apoptosis is reduced only in TLR4−/− and TRIF−/− mice. As expected, DC apoptosis induced by the TLR4 ligand LPS is also abolished in these mice. Injection of the TLR9 ligand CpG-oligodeoxynucleotide (synthetic bacterial DNA) induces DC migration and maturation, but only modest DC apoptosis when compared with LPS and E. coli. Together, these results suggest that E. coli bacteremia directly impacts on DC maturation and survival in vivo through a TLR4-TRIF-dependent signaling pathway.

Myd88-Dependent In Vivo Maturation of Splenic Dendritic Cells Induced by Leishmania donovani and Other Leishmania Species

ABSTRACT The usual agent of visceral leishmaniasis in the Old World is Leishmania donovani, which typically produces systemic diseases in humans and mice. L. donovani has developed efficient strategies to infect and persist in macrophages from spleen and liver. Dendritic cells (DC) are sentinels of the immune system. Following recognition of evolutionary conserved microbial products, DC undergo a maturation process and activate antigen-specific naïve T cells. In the present report we provide new insights into how DC detect Leishmania in vivo. We demonstrate that in both C57BL/6 and BALB/c mice, systemic injection of L. donovani induced the migration of splenic DC from marginal zones to T-cell areas. During migration, DC upregulated the expression of major histocompatibility complex II and costimulatory receptors (such as CD40, CD80, and CD86). Leishmania-induced maturation requires live parasites and is not restricted to L. donovani, as L. braziliensis, L. major, and L. mexicana induced a similar process. Using a green fluorescent protein-expressing parasite, we demonstrate that DC undergoing maturation in vivo display no parasite internalization. We also show that L. donovani-induced DC maturation was partially abolished in MyD88-deficient mice. Taken together, our data suggest that Leishmania-induced DC maturation results from direct recognition of Leishmania by DC, and not from DC infection, and that MyD88-dependent receptors are implicated in this process.

T Cell-Dependent Maturation of Dendritic Cells in Response to Bacterial Superantigens

Dendritic cells (DC) express a set of germline-encoded transmembrane Toll-like receptors that recognize shared microbial products, such as Escherichia coli LPS, termed pathogen-associated molecular patterns. Analysis of the in vivo response to pathogen-associated molecular patterns has uncovered their ability to induce the migration and the maturation of DC, favoring thus the delivery of Ag and costimulatory signals to naive T cells in vivo. Bacterial superantigens constitute a particular class of pathogen-derived molecules known to induce a potent inflammatory response in vivo, secondary to the activation of a large repertoire of T cells. We demonstrate in this work that Staphylococcal superantigens induce migration and maturation of DC populations in vivo. However, in contrast to LPS, superantigens failed to induce DC maturation in RAG or MHC class II-deficient mice, suggesting that T cell activation was a prerequisite for DC maturation. This conclusion was further supported by the finding that T cell activation induced by 1) mitogenic anti-CD3 mAbs, 2) allo-MHC determinants, or 3) nominal Ag in a TCR-transgenic model induces DC maturation in vivo. These studies also revealed that DC that matured in response to T cell mitogens display, comparatively to LPS, a distinctive phenotype characterized by high expression of the MHC class II, CD40, and CD205 markers, but only moderate (CD86) to minimal (CD80) expression of CD28/CTLA4 ligands. This work demonstrates that activation of a sufficient number of naive T cells in vivo constitutes a novel form of immune danger, functionally linked to DC maturation.

Formyl Peptide Receptor-Like 2 Is Expressed and Functional in Plasmacytoid Dendritic Cells, Tissue-Specific Macrophage Subpopulations, and Eosinophils

The formyl peptide receptor (FPR) is a key player in innate immunity and host defense mechanisms. In humans and other primates, a cluster of genes encodes two related receptors, FPR-like 1 and FPR-like 2 (FPRL1 and FPRL2). Despite their high sequence similarity, the three receptors respond to different sets of ligands and display a different expression pattern in leukocyte populations. Unlike FPR and FPRL1, FPRL2 is absent from neutrophils, and two endogenous peptide agonists, F2L and humanin, were recently described. In the present work, we investigated the detailed functional distribution of FPRL2 in leukocytes by quantitative PCR, flow cytometry, immunohistochemistry, and chemotaxis assays, with the aim of raising hypotheses regarding its potential functions in the human body. We describe that FPRL2 is highly expressed and functional in plasmacytoid dendritic cells and up-regulated upon their maturation. FPRL2 is also expressed in eosinophils, which are recruited but do not degranulate in response to F2L. FPRL2 is expressed and functional in macrophages differentiated from monocytes in vitro in different conditions. However, in vivo, only specific subsets of macrophages express the receptor, particularly in the lung, colon, and skin, three organs chronically exposed to pathogens and exogenous aggressions. This distribution and the demonstration of the production of the F2L peptide in mice underline the potential role of FPRL2 in innate immunity and possibly in immune regulation and allergic diseases.

The Idiotypic Network: Order from the Beginning or Order out of Chaos?

Some years ago, we came upon the concept of the idiotypic network (Jerne 1974) on the basis of some unexpected findings and because of a prejudice in favor of germ-line theories (Urbain et al. 1972; Urbain 1974; Urbain 1976). At that time, there was controversy between adherents of the somatic mutation theory and “hard-nosed” germ liners.

Self-nonself discrimination in the immune system. A broken idiotypic mirror

Before a general theory of immunoregulation can be put forward, the research worker is faced with a t least three major problems to solve. The first is understanding the mechanisms allowing self-nonself discrimination. A self-antigen (S) is one that is continuously present from the beginning and exposed to the immature immune system, whereas a foreign antigen is present only transiently and is usually absent when the immune system matures. Many persons term self-antigens all antigenic structures that are encoded by the individual’s germline. However, no one knows, for example, if a ribosomal protein is considered a self-antigen by the immune system. Are some internal cellular constituents processed and continuously exposed on the cell membrane, as suggested by recent work?192 Until now, two major concepts have been used to explain natural tolerance. One theory holds that immature B cells (or T cells) are especially sensitive to negative signaling. Immature B lymphocytes are inactivated as soon as they encounter self-antigens. (For a review, see reference 3.) This “clonal anergy” of early B lymphocytes could be followed by activation of suppressor circuits that will allow maintenance of the “tolerant ~ t a t e . ” ~ In another theory, every B lymphocyte, whether immature or not, is paralyzable or inducible. Transduction of one signal, induced by antigen or antiidiotype, would lead to unresponsiveness, whereas the same signal associated with a second signal (cooperative help) would promote differentiation of the B lympho~yte.~” The exquisite sensitivity of immature B lymphocytes to negative signaling is well d~cumented .~**~ Some facts support the Occurrence of suppressor circuits. Whatever the correct theory, the network theory seems to stand in sharp contradiction to the self-nonself discrimination phenomenon. The idiotype network rests on the assumption (which is demonstrated experimentally) that complementary partners (idiotypes and antiidiotypes) coexist within the repertoire of a single Therefore, as complementary lymphocytes emerge, they will cancel each other by virtue of selfrecognition, leading to the paradox of the empty repertoire: diversity disappears as soon as it appears. CohngVLo has repeatedly stressed that no network theory is possible because there is no way to distinguish a self-epitope from a self-idiotope. One goal of this report is to suggest that a network theory is possible on the basis of the self-nonself discrimination phenomenon. The second problem of immunoregulation is the selection of actual and available

The influence of Vκ gene polymorphism on the induction of silent idiotypes in the arsonate system

It has been previously shown that it is possible to modify the expressed repertoire of a given individual using idiotypic manipulation. For example, A/J mice respond to arsonate challenge by synthesizing a dominant idiotype, CRIA, whereas BALB/c mice do not. However, after treatment with rabbit polyclonal anti-CRIA antibodies (Ab2 or anti-idiotypic antibodies) and arsonate, BALB/c mice are able to synthesize a CRIA-like idiotype. To determine whether this modification of repertoire is dependent on the immunoglobulin loci (Ig-h, kappa), we have analyzed the anti-arsonate response after anti-idiotypic treatment of three strains of mice (C58, C.C58, AKR), chosen because they are among a small group of strains which express Kappa V regions not seen in other strains. There are also L chains lacking in these strains which are expressed in other mice. The C58 and C.C58 strains share the same Ig-h locus (Ig-ha) with BALB/c mice but C.C58 are congenic mice, that express the kappa loci on a BALB/c genetic background. AKR mice express the Ig-hd haplotype. AKR, C58 and C.C58 do not produce CRIA positive antibodies in response to arsonate; a defect which has been previously mapped to the kappa locus. These three strains of mice (C58, C.C58 and AKR) were treated with rabbit anti-CRIA and boosted with Ars-KLH. The results show that after such treatment, the C.C58 mice were able to express CRIA-like antibodies which are serologically identical to those of BALB/c.

Distinct VH repertoires in primary and secondary B cell lymphocyte subsets in the preimmune repertoire of A/J mice: the CRI‐A idiotype is preferentially associated with the HSAlow B cell subset

The anti‐arsonate immune response of A/J mice is characterized by the occurrence of several recurrent idiotypes with a different temporal pattern of expression. The CRI‐A idiotype is typically a memory idiotype since it appears late in the primary and dominates the secondary as well as subsequent immune responses. The CRI‐C idiotype is present throughout the responses, including the primary one. Naive adult A/J mice treated repeatedly with anti‐μ or anti‐δ monoclonal antibodies exhibit a completely different balance of HSAlow and HSAhigh B cell subsets and an opposite idiotype profile after immunization with p‐azophenylarsonate coupled to hemocyanin. Anti‐μ  treatment leads to a striking enhancement of the HSAlow cell subset associated with an earlier important synthesis of CRI‐A+ antibodies, while anti‐δ treatment enhances significantly the HSAhigh compartment with a strong decrease of CRI‐A and persistence of CRI‐C1 antibodies. Semiquantitative PCR analysis reveals that the presence of CRI‐A transcripts is associated with the HSAlow compartment, while CRI‐C transcripts are mainly associated with HSAhigh B cell subsets. This has been demonstrated with spleen cells of adult A/J mice treated with anti‐μ or anti‐δ antibodies and also with purified B cell subsets of unimmunized adult A/J mice and on neonatal spleen cells. It appears that the memory (CRI‐A) idiotype is selected into the HSAlow B cell subset before antigen arrival.

Selection of Anti-Arsonate Idiotype (CRIA) in A/J Mice by the Immune Network

A/J mice immunized against arsonate (ARS) coupled to hemocyanin (KLH) synthesize a cross reactive idiotype named CRIA (Kuettner et al., 1972). This idiotype is encoded by a single combination of genes called the canonical combination which is constituted of one VH gene (VHIdCR11), one D segment (DFL16.1), one JH segment (JH2), one VK gene (VKIdCR) and one JK segment (JK1).