Klaus I. Matthaei

IL-5-Deficient Mice Have a Developmental Defect in CD5+ B-1 Cells and Lack Eosinophilia but Have Normal Antibody and Cytotoxic T Cell Responses

Mice deficient in interleukin-5 (IL-5-/- mice) were generated by gene targeting in embryonal stem cells. Contrary to previous studies, no obligatory role for IL-5 was demonstrated in the regulation of conventional B (B-2) cells, in normal T cell-dependent antibody responses or in cytotoxic T cell development. However, CD5+ B cells (B-1 cells) in the peritoneal cavity were reduced by 50%-80% in 2-week-old IL-5-/- mice, returning to normal by 6-8 weeks of age. The IL-5-/- mice did not develop blood and tissue eosinophilia when infected with the helminth Mesocestoides corti, but basal levels of eosinophils with normal morphology were produced in the absence of IL-5. IL-5 deficiency did not affect the worm burden of infected mice, indicating that increased eosinophils do not play a significant role in the host defence in this parasite model.

Relationship between interleukin-5 and eotaxin in regulating blood and tissue eosinophilia in mice.

The mechanism of cooperation between IL-5 and eotaxin for the selective accumulation of eosinophils at sites of allergic inflammation is unknown. In this investigation we have used IL-5 deficient mice to define the relationship between this cytokine and eotaxin in the regulation of blood eosinophilia and eosinophil homing and tissue accumulation. Both IL-5 and eotaxin could independently induce a rapid and pronounced blood eosinophilia in wild type mice when administered systemically. In contrast, only eotaxin induced a pronounced blood eosinophilia in IL-5 deficient mice. The eosinophilic response induced by intravenous eotaxin in wild type mice did not correlate with a significant reduction in the level of bone marrow eosinophils, whereas intravenous IL-5 resulted in depletion of this store. These results suggest the existence of two mechanisms by which eosinophils can be rapidly mobilized in response to intravenous eosinophil chemoattractants; first, mobilization of an IL-5 dependent bone marrow pool, and second, an eotaxin-induced sequestration of eosinophils from tissues into the blood. Subcutaneous injection of eotaxin induced a local tissue eosinophilia in wild type mice but not in IL-5 deficient mice. Furthermore, tissue eosinophilia in wild type mice, but not in IL-5 deficient mice, was enhanced by adoptive transfer of eosinophils or the administration of intravenous IL-5. However, pretreatment of IL-5 deficient mice with intraperitoneal IL-5 for 72 h restored eosinophil homing and tissue accumulation in response to subcutaneous eotaxin. We propose that eotaxin secreted from inflamed tissue may play an important role in initiating both blood and tissue eosinophilia in the early phases of allergic inflammation. Furthermore, IL-5 is not only essential for mobilizing eosinophils from the bone marrow during allergic inflammation, but also plays a critical role in regulating eosinophil homing and migration into tissues in response to eotaxin and possibly other specific chemotactic stimuli.

Intrinsic Defect in T Cell Production of Interleukin (IL)-13 in the Absence of Both IL-5 and Eotaxin Precludes the Development of Eosinophilia and Airways Hyperreactivity in Experimental Asthma

Interleukin (IL)-5 and IL-13 are thought to play key roles in the pathogenesis of asthma. Although both cytokines use eotaxin to regulate eosinophilia, IL-13 is thought to operate a separate pathway to IL-5 to induce airways hyperreactivity (AHR) in the allergic lung. However, identification of the key pathway(s) used by IL-5 and IL-13 in the disease process is confounded by the failure of anti–IL-5 or anti–IL-13 treatments to completely inhibit the accumulation of eosinophils in lung tissue. By using mice deficient in both IL-5 and eotaxin (IL-5/eotaxin−/−) we have abolished tissue eosinophilia and the induction of AHR in the allergic lung. Notably, in mice deficient in IL-5/eotaxin the ability of CD4+ T helper cell (Th)2 lymphocytes to produce IL-13, a critical regulator of airways smooth muscle constriction and obstruction, was significantly impaired. Moreover, the transfer of eosinophils to IL-5/eotaxin−/− mice overcame the intrinsic defect in T cell IL-13 production. Thus, factors produced by eosinophils may either directly or indirectly modulate the production of IL-13 during Th2 cell development. Our data show that IL-5 and eotaxin intrinsically modulate IL-13 production from Th2 cells and that these signaling systems are not necessarily independent effector pathways and may also be integrated to regulate aspects of allergic disease.

Histone variant H2A.Z is required for early mammalian development

Fundamental to the process of mammalian development is the timed and coordinated regulation of gene expression. This requires transcription of a precise subset of the total complement of genes. It is clear that chromatin architecture plays a fundamental role in this process by either facilitating or restricting transcription factor binding [1]. How such specialized chromatin structures are established to regulate gene expression is poorly understood. All eukaryotic organisms contain specialized histone variants with distinctly different amino acid sequences that are even more conserved than the major core histones [2]. On the basis of their highly conserved sequence, histone variants have been assumed critical for the function of mammalian chromatin; however, a requirement for a histone variant has not been shown in mammalian cells. Mice with a deletion of H1 degrees have been generated by gene targeting in ES cells, but these mice show no phenotypic consequences, perhaps due to redundancy of function [3]. Here we show for the first time that a mammalian histone variant, H2A.Z, plays a critical role in early development, and we conclude that this histone variant plays a pivotal role in establishing the chromatin structures required for the complex patterns of gene expression essential for normal mammalian development.

Elemental signals regulating eosinophil accumulation in the lung

Summary: In this review we identify the elemental signals that regulate eosinophil accumulation in the allergic lung. We show that there are two interwoven mechanisms for the accumulation of eosinophils in pulmonary tissues and that these mechanisms are linked to the development of airways hyperreactivity (AHR). Interleukin‐(IL)‐5 plays a critical role in the expansion of eosinophil pools in both the bone marrow and blood in response to allergen provocation of the airways. Secondly, IL‐4 and IL‐13 operate within the allergic lung to control the transmigration of eosinophils across the vascular bed into pulmonary tissues. This process exclusively promotes tissue accumulation of eosinophils. IL‐13 and IL‐4 probably act by activating eosinophil‐specific adhesion pathways and by regulating the production of IL‐5 and eotaxin in the lung compartment. IL‐5 and eotaxin co‐operate locally in pulmonary tissues to selectively and synergistically promote eosinophilia. Thus, IL‐5 acts systemically to induce eosinophilia and within tissues to promote local chemotactic signals. Regulation of IL‐5 and eotaxin levels within the lung by IL‐4 and IL‐13 allows Th2 cells to elegantly co‐ordinate tissue and peripheral eosinophilia. Whilst the inhibition of either the IL‐4/IL‐13 or IL‐5/ eotaxin pathways resulted in the abolition of tissue eosinophils and AHR, only depletion of IL‐5 and eotaxin concurrently results in marked attenuation of pulmonary inflammation. These data highlight the importance of targeting both IL‐5 and CCR3 signalling systems for the resolution of inflammation and AHR associated with asthma.

IL-9– and mast cell–mediated intestinal permeability predisposes to oral antigen hypersensitivity

Previous mouse and clinical studies demonstrate a link between Th2 intestinal inflammation and induction of the effector phase of food allergy. However, the mechanism by which sensitization and mast cell responses occurs is largely unknown. We demonstrate that interleukin (IL)-9 has an important role in this process. IL-9–deficient mice fail to develop experimental oral antigen–induced intestinal anaphylaxis, and intestinal IL-9 overexpression induces an intestinal anaphylaxis phenotype (intestinal mastocytosis, intestinal permeability, and intravascular leakage). In addition, intestinal IL-9 overexpression predisposes to oral antigen sensitization, which requires mast cells and increased intestinal permeability. These observations demonstrate a central role for IL-9 and mast cells in experimental intestinal permeability in oral antigen sensitization and suggest that IL-9–mediated mast cell responses have an important role in food allergy.

Toll/IL-1 Signaling Is Critical for House Dust Mite―specific Th1 and Th2 Responses

RATIONALE One of the immunopathological features of allergic inflammation is the infiltration of helper T type 2 (Th2) cells to the site of disease. Activation of innate pattern recognition receptors such as Toll-like receptors (TLRs) plays a critical role in helper T type 1 cell differentiation, yet their contribution to the generation of Th2 responses to clinically relevant aeroallergens remains poorly defined. OBJECTIVES To determine the requirement for TLR2, TLR4, and the Toll/IL-1 receptor domain adaptor protein MyD88 in a murine model of allergic asthma. METHODS Wild-type and factor-deficient ((-/-)) mice were sensitized intranasally to the common allergen house dust mite (HDM) and challenged 2 weeks later on four consecutive days. Measurements of allergic airway inflammation, T-cell cytokine production, and airway hyperreactivity were performed 24 hours later. MEASUREMENTS AND MAIN RESULTS Mice deficient in MyD88 were protected from the cardinal features of allergic asthma, including granulocytic inflammation, Th2 cytokine production and airway hyperreactivity. Although HDM activated NF-kappaB in TLR2- or TLR4-expressing HEK cells, only in TLR4(-/-) mice was the magnitude of allergic airway inflammation and hyperreactivity attenuated. The diminished Th2 response present in MyD88(-/-) and TLR4(-/-) mice was associated with fewer OX40 ligand-expressing myeloid dendritic cells in the draining lymph nodes during allergic sensitization. Finally, HDM-specific IL-17 production and airway neutrophilia were attenuated in MyD88(-/-) but not TLR4(-/-) mice. CONCLUSIONS Together, these data suggest that Th2- and Th17-mediated inflammation generated on inhalational HDM exposure is differentially regulated by the presence of microbial products and the activation of distinct MyD88-dependent pattern recognition receptors.

IL-13 Induces Airways Hyperreactivity Independently of the IL-4Rα Chain in the Allergic Lung

The potent spasmogenic properties of IL-13 have identified this molecule as a potential regulator of airways hyperreactivity (AHR) in asthma. Although IL-13 is thought to primarily signal through the IL-13Rα1-IL-4Rα complex, the cellular and molecular components employed by this cytokine to induce AHR in the allergic lung have not been identified. By transferring OVA-specific CD4+ T cells that were wild type (IL-13+/+ T cells) or deficient in IL-13 (IL-13−/− T cells) to nonsensitized mice that were then challenged with OVA aerosol, we show that T cell-derived IL-13 plays a key role in regulating AHR, mucus hypersecretion, eotaxin production, and eosinophilia in the allergic lung. Moreover, IL-13+/+ T cells induce these features (except mucus production) of allergic disease independently of the IL-4Rα chain. By contrast, IL-13+/+ T cells did not induce disease in STAT6-deficient mice. This shows that IL-13 employs a novel component of the IL-13 receptor signaling system that involves STAT6, independently of the IL-4Rα chain, to modulate pathogenesis. We show that this novel pathway for IL-13 signaling is dependent on T cell activation in the lung and is critically linked to downstream effector pathways regulated by eotaxin and STAT6.

Toll-Interleukin-1 signalling is critical for house mite-specific th2 and th17 responses

RATIONALE One of the immunopathological features of allergic inflammation is the infiltration of helper T type 2 (Th2) cells to the site of disease. Activation of innate pattern recognition receptors such as Toll-like receptors (TLRs) plays a critical role in helper T type 1 cell differentiation, yet their contribution to the generation of Th2 responses to clinically relevant aeroallergens remains poorly defined. OBJECTIVES To determine the requirement for TLR2, TLR4, and the Toll/IL-1 receptor domain adaptor protein MyD88 in a murine model of allergic asthma. METHODS Wild-type and factor-deficient ((-/-)) mice were sensitized intranasally to the common allergen house dust mite (HDM) and challenged 2 weeks later on four consecutive days. Measurements of allergic airway inflammation, T-cell cytokine production, and airway hyperreactivity were performed 24 hours later. MEASUREMENTS AND MAIN RESULTS Mice deficient in MyD88 were protected from the cardinal features of allergic asthma, including granulocytic inflammation, Th2 cytokine production and airway hyperreactivity. Although HDM activated NF-kappaB in TLR2- or TLR4-expressing HEK cells, only in TLR4(-/-) mice was the magnitude of allergic airway inflammation and hyperreactivity attenuated. The diminished Th2 response present in MyD88(-/-) and TLR4(-/-) mice was associated with fewer OX40 ligand-expressing myeloid dendritic cells in the draining lymph nodes during allergic sensitization. Finally, HDM-specific IL-17 production and airway neutrophilia were attenuated in MyD88(-/-) but not TLR4(-/-) mice. CONCLUSIONS Together, these data suggest that Th2- and Th17-mediated inflammation generated on inhalational HDM exposure is differentially regulated by the presence of microbial products and the activation of distinct MyD88-dependent pattern recognition receptors.

Immunopathogenesis of Experimental Ulcerative Colitis Is Mediated by Eosinophil Peroxidase

The precise role that individual inflammatory cells and mediators play in the development of gastrointestinal (GI) dysfunction and extraintestinal clinical manifestations of ulcerative colitis (UC) is unknown. In this study, we have used a mouse model of UC to establish a central role for eotaxin and, in turn, eosinophils in the development of the immunopathogenesis of this disease. In this model the administration of dextran sodium sulfate (DSS) induces a prominent colonic eosinophilic inflammation and GI dysfunction (diarrhea with blood and shortening of the colon) that resembles UC in patients. GI dysfunction was associated with evidence of eosinophilic cytolytic degranulation and the release of eosinophil peroxidase (EPO) into the colon lumen. By using IL-5 or eotaxin-deficient mice, we show an important role for eotaxin in eosinophil recruitment into the colon during experimental UC. Furthermore, using EPO-deficient mice and an EPO inhibitor resorcinol we demonstrate that eosinophil-derived peroxidase is critical in the development of GI dysfunction in experimental UC. These findings provide direct evidence of a central role for eosinophils and EPO in GI dysfunction and potentially the immunopathogenesis of UC.