Jean-Paul Papin

Peroxisome Proliferator–activated Receptors α and γ Down-regulate Allergic Inflammation and Eosinophil Activation

Allergic asthma is characterized by airway hyperresponsiveness, eosinophilia, and mucus accumulation and is associated with increased IgE concentrations. We demonstrate here that peroxisome proliferator–activated receptors (PPARs), PPAR-α and PPAR-γ, which have been shown recently to be involved in the regulation of various cell types within the immune system, decrease antigen-induced airway hyperresponsiveness, lung inflammation, eosinophilia, cytokine production, and GATA-3 expression as well as serum levels of antigen-specific IgE in a murine model of human asthma. In addition, we demonstrate that PPAR-α and -γ are expressed in eosinophils and their activation inhibits in vitro chemotaxis and antibody-dependent cellular cytotoxicity. Thus, PPAR-α and -γ (co)agonists might be of therapeutic interest for the regulation of allergic or inflammatory reactions by targeting both regulatory and effector cells involved in the immune response.

Peroxisome proliferator-activated receptor α regulates skin inflammation and humoral response in atopic dermatitis

BACKGROUND The peroxisome proliferator-activated receptors (PPARs) alpha, beta/delta, and gamma are ligand-activated transcription factors belonging to the nuclear receptor superfamily. In addition to their regulatory role on lipid and glucose metabolism, they exert anti-inflammatory properties. In skin both PPAR-alpha and PPAR-beta/delta regulate keratinocyte proliferation/differentiation and contribute to wound healing. The 3 PPAR isoforms are expressed by several cell types recruited into the dermis during inflammation. OBJECTIVE We have investigated the role of PPAR-alpha in the regulation of atopic dermatitis (AD), a common skin inflammatory disease. METHODS We chose a mouse model of inflammatory dermatosis with immunologic features of AD and used epicutaneous sensitization with ovalbumin in the absence of adjuvant, which mimics the human pathology. RESULTS On antigen sensitization, PPAR-alpha-deficient mice display increased epidermal thickening, dermal recruitment of inflammatory cells, lung inflammation, airway hyperresponsiveness, and IgE and IgG2a production compared with their wild-type counterparts. Increased inflammation was correlated to an enhancement of TH2 and, to a greater extent, TH1 responses and to increased skin expression of nuclear factor kappaB. Interestingly, PPAR-alpha expression was decreased in eczematous skin from patients with AD compared with skin from nonatopic donors, suggesting that defective PPAR-alpha expression might contribute to the pathology. Topical application of WY14643, a specific PPAR-alpha agonist, significantly decreased antigen-induced skin inflammation in the AD model. CONCLUSION PPAR-alpha acts as a negative regulator of skin inflammation in AD.

Expression of a Functional FcεRI on Rat Eosinophils and Macrophages

Besides its crucial role in type I hypersensitivity reactions, IgE is involved in anti-parasite immunity. This role has been clearly demonstrated in both human and rat schistosomiasis, but remains controversial in the mouse. Since the cellular distribution of the high affinity IgE receptor, FcεRI, differs in humans and mice, it might explain the differences in effector function of IgE between the two species. In humans, eosinophils and macrophages induce IgE-dependent cytotoxicity toward Schistosoma mansoni larvae, which involves FcεRI in the case of eosinophils. In the present study, we have investigated the expression and function of FcεRI in rat eosinophils and macrophages. We demonstrate, by flow cytometry, fluorescence microscopy, and Western blot analysis, that in rats, as in humans, a functional αγ2 trimeric FcεRI is expressed on eosinophils and macrophages. We also show that these two cell types can induce IgE-mediated, FcεRI-dependent cellular cytotoxicity toward schistosomula. These results thus provide a molecular basis for the differences observed between rat and mouse regarding IgE-mediated anti-parasite immunity.

Eosinophil-derived IFN-γ induces airway hyperresponsiveness and lung inflammation in the absence of lymphocytes

BACKGROUND Eosinophils are key players in T(H)2-driven pathologies, such as allergic lung inflammation. After IL-5- and eotaxin-mediated tissue recruitment, they release several cytotoxic and inflammatory mediators. However, their exact contribution to asthma remains controversial. Indeed, in human subjects anti-IL-5 treatment inhibits eosinophilia but not antigen-induced airway hyperresponsiveness (AHR). Likewise, lung fibrosis is abrogated in 2 strains of eosinophil-deficient mice, whereas AHR is inhibited in only one of them. Finally, eosinophils have been shown to attract T(H)2 lymphocytes at the inflammatory site. OBJECTIVE The ability of eosinophils to promote AHR and lung inflammation independently of lymphocytes was investigated. METHODS Adoptive transfers of resting or activated eosinophils from IL-5 transgenic mice were performed into naive BALB/c mice, mice with severe combined immunodeficiency, and IFN-gamma-deficient BALB/c recipients. RESULTS Adoptively transferred eosinophils induced lung inflammation, fibrosis, collagen deposition, and AHR not only in BALB/c mice but also in recipient mice with severe combined immunodeficiency. Surprisingly, IFN-gamma expression was increased in lungs from eosinophil-transferred animals. Furthermore, IFN-gamma neutralization in recipients partially inhibited eosinophil-induced AHR. Moreover, IFN-gamma-deficient eosinophils or eosinophils treated with a blocking anti-IFN-gamma receptor antibody failed to induce AHR in IFN-gamma-deficient recipients. Finally, in vitro and at low concentrations, IFN-gamma increased eosinophil peroxidase release, potentiated chemotaxis, and prolonged survival, suggesting the existence of an autocrine mechanism. CONCLUSIONS These results support the important and previously unsuspected contribution of eosinophils to lung inflammation independently of lymphocytes through production of IFN-gamma, the prototypical T(H)1 cytokine.

Interactions between eosinophils and antibodies: In vivo protective role against rat schistosomiasis☆

An original protocol of cell transfer from Schistosoma mansoni-infected rats to normal recipient rats is used to investigate the protective role of phagocytic cell populations, described as effector cells in vitro, against a challenge infection with S. mansoni. Nonadherent, eosinophil-enriched and -adherent, macrophage-rich cell preparations, injected via intradermal and subcutaneous routes at the precise site of exposure to cercariae, were able to significantly protect the recipient rats. The time-course study of this protective effect according to the time after infection of donor rats revealed that eosinophils were the major cell population involved in the early phase of infection (4 to 5 weeks), whereas macrophages could also be incriminated thereafter. A rosette assay using anti-immunoglobulin-coated erythrocytes indicated a sequence of the various antibody isotypes under study (IgG1, IgG2a, IgE) on the eosinophil surface, during the course of infection. As previously shown in vitro, cytophilic antibodies seemed to participate in the protective effect of eosinophils, since eosinophil-enriched cells from normal rats, sensitized in vitro with immune complexes present in infected rat serum, could also confer significant protection. These observations establish therefore the relevance between our previous in vitro studies and rat resistance to a challenge infection with S. mansoni, underlining the major role played by the interaction between antibodies and phagocytic cells (eosinophils and macrophages).

Selectin and Lewisx are required as co‐receptors in antibody‐dependent cell‐mediated cytotoxicity of human eosinophils to Schistosoma mansoni schistosomula

Killing of Schistosoma mansoni larvae by human eosinophils via antibody‐dependent cell‐mediated cytotoxicity (ADCC) mechanisms requires adherence between effector cells and parasite targets. The role of adhesion molecules in this mechanism was investigated using blocking monoclonal antibodies (mAb) and soluble ligands. We show that, along with the Mac‐1 α chain, interactions between selectins and Lewisx ‐related structures, both expressed by eosinophils and parasite targets, play a critical part in the antibody‐dependent cytotoxic function of eosinophils. To further elucidate the interactions between adhesion molecules and eosinophil Fc receptors, ADCC was performed with IgG1 or IgA mAb. We found that mAb directed against Mac‐1 α chain or against Lewisx could significantly inhibit the IgG1‐, but not IgA cytotoxicity. This result might be explained, at least in part, by the inhibitory effect of these mAb on the release by eosinophils of eosinophil cationic protein, one of the major mediators involved in target killing. Taken together, these results suggest novel interactions between Fc receptors and selectins and Lewisx ‐related structures which might act as co‐receptors for eosinophil‐mediated cytotoxicity.

FcεRI and FcγRIII/CD16 Differentially Regulate Atopic Dermatitis in Mice

The high-affinity IgE receptor FcεRI and, in some models, the low-affinity IgG receptor FcγRIII/CD16 play an essential role in allergic diseases. In human skin, they are present on APCs and effector cells recruited into the inflamed dermis. FcRγ is a subunit shared, among other FcRs, by FcεRI and CD16 and is essential to their assembly and signal transduction. Using an experimental model reproducing some features of human atopic dermatitis and specific FcR-deficient mice, we have herein delineated the respective contribution of FcεRI and FcγRIII/CD16 to the pathology. We demonstrate that symptoms of atopic dermatitis are completely absent in FcRγ-deficient animals but only partially inhibited in either FcεRI- or FcγRIII/CD16-deficient animals. Absence or attenuation of the pathology is correlated to increased skin expression of regulatory IL-10 and Foxp3. While FcεRI controls both Th1 and Th2 skin response, mast cell recruitment into draining lymph nodes and IgE production, CD16 regulates only Th2 skin response, as well as T cell proliferation and IgG1 production. This isotype-specific regulation by the cognate FcR is associated to a differential regulation of IL-4 and IL-21 expression in the draining lymph nodes. FcεRI and CD16 thus contribute to atopic dermatitis but differentially regulate immune responses associated with the disease. Targeting both IgE/FcεRI and IgG/CD16 interactions might represent an efficient therapeutic strategy for allergic diseases.

Inhibitory Effects of Lodoxamide on Eosinophil Activation

Recent reports describe the beneficial use of lodoxamide, an anti-allergic compound, for the treatment of asthma and allergic conjunctivitis. Lodoxamide is known as a mast cell stabilizer, however, the association of a significant clinical improvement with a specific decrease in eosinophil infiltrate suggested possible direct effects of lodoxamide on eosinophils. The chemotactic response of eosinophils to fMLP as well as to IL-5, in vitro, was very significantly and dose-dependently inhibited by Lodoxamide. Lodoxamide was also able to strongly inhibit the release of eosinophil peroxidase after IgA-dependent activation and, to a lesser extent, the release of eosinophil cationic protein and eosinophil-derived neurotoxin. Moreover, the release of cytotoxic mediators evaluated in an antibody-dependent cytotoxicity assay against parasitic targets was also significantly reduced, not only in the case of human eosinophils but also in a rat eosinophil-mast cell model of cytotoxicity. Taken together, these results indicate that lodoxamide can exert potent inhibitory effects on eosinophil activation in vitro combined with a strong inhibition of eosinophil attraction, leading therefore to a reduction in their pathological potential in vivo.

From allergy to schistosomes: role of Fc receptors and adhesion molecules in eosinophil effector function

The dual function of eosinophils has been evidenced in protective immunity against parasites as well as in pathological manifestations during allergic disorders. We have demonstrated that a new class of IgE receptors, Fc epsilon RII/CD23, was involved in the functional duality of eosinophils and other proinflammatory cells. More recently, we have shown that Fc epsilon RI, the high affinity IgE receptor thought to be only expressed by basophils and most cells, was involved in eosinophil-mediated cytotoxicity against schistosomes as well as in mediator release. These results favour the view that both IgE and its receptors have been primarily associated to a protective immune response, rather than to pathology. Not only IgE receptors but also members belonging to the family of adhesion molecules can participate as co-receptors in eosinophil effector function. The inhibitory role of monoclonal antibodies to Lewis(X) (Le(X) CD15) or to selectins in eosinophil-mediated cytotoxicity towards schistosomes and the detection of Le(X) and selectin-like molecules on schistosomula surface indicate a double interaction mediated by selectins and their carbohydrate ligands between eosinophils and schistosomula. These results suggest new functions for these adhesion molecules, previously known to be involved mainly in cell infiltration.