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Eosinophils are effectors in immunity to tissue helminths but also induce allergic immunopathology. Mechanisms of eosinophilia in non-mucosal tissues during infection remain unresolved. Here we identify a pivotal function of tissue macrophages (Mϕ) in eosinophil anti-helminth immunity using a BALB/c mouse intra-peritoneal Brugia malayi filarial infection model. Eosinophilia, via C-C motif chemokine receptor (CCR)3, was necessary for immunity as CCR3 and eosinophil impairments rendered mice susceptible to chronic filarial infection. Post-infection, peritoneal Mϕ populations proliferated and became alternatively-activated (AAMϕ). Filarial AAMϕ development required adaptive immunity and interleukin-4 receptor-alpha. Depletion of Mϕ prior to infection suppressed eosinophilia and facilitated worm survival. Add back of filarial AAMϕ in Mϕ-depleted mice recapitulated a vigorous eosinophilia. Transfer of filarial AAMϕ into Severe-Combined Immune Deficient mice mediated immunological resistance in an eosinophil-dependent manner. Exogenous IL-4 delivery recapitulated tissue AAMϕ expansions, sustained eosinophilia and mediated immunological resistance in Mϕ-intact SCID mice. Co-culturing Brugia with filarial AAMϕ and/or filarial-recruited eosinophils confirmed eosinophils as the larvicidal cell type. Our data demonstrates that IL-4/IL-4Rα activated AAMϕ orchestrate eosinophil immunity to filarial tissue helminth infection.

Background Due to the post-mitotic nature of myonuclei, postnatal myogenesis is essential for skeletal muscle growth, repair, and regeneration. This process is facilitated by satellite cells through proliferation, differentiation, and subsequent fusion with a pre-existing muscle fiber (i.e., myonuclear accretion). Current knowledge of myogenesis is primarily based on the in vitro formation of syncytia from myoblasts, which represents aspects of developmental myogenesis, but may incompletely portray postnatal myogenesis. Therefore, we aimed to develop an in vitro model that better reflects postnatal myogenesis, to study the cell intrinsic and extrinsic processes and signaling involved in the regulation of postnatal myogenesis. Methods Proliferating C2C12 myoblasts were trypsinized and co-cultured for 3 days with 5 days differentiated C2C12 myotubes. Postnatal myonuclear accretion was visually assessed by live cell time-lapse imaging and cell tracing by cell labeling with Vybrant® DiD and DiO. Furthermore, a Cre/LoxP-based cell system was developed to semi-quantitatively assess in vitro postnatal myonuclear accretion by the conditional expression of luciferase upon myoblast–myotube fusion. Luciferase activity was assessed luminometrically and corrected for total protein content. Results Live cell time-lapse imaging, staining-based cell tracing, and recombination-dependent luciferase activity, showed the occurrence of postnatal myonuclear accretion in vitro. Treatment of co-cultures with the myogenic factor IGF-I (p

Mast cell numbers are markedly increased at sites of chronic inflammation. However, the underlying mechanisms of mast cell accumulation including mast cell progenitor trafficking remain to be identified in detail. Thus, the aim of this study was to identify the adhesion molecules involved in rolling, firm adhesion and transendothelial diapedesis of murine bone marrow-derived cultured mast cells (BMCMC) as a model for immature mast cells. We could show that BMCMCs exhibit in vivo rolling on skin vessel walls and strong adhesion to skin endothelial cells (ECs) in vitro under static and flow conditions. Interestingly, interaction of BMCMC with the EC adhesion molecules E- and P-selectin, vascular cell adhesion molecule-1 (VCAM-1) and platelet endothelial cell adhesion molecule-1 (PECAM-1) is required to mediate rolling and firm adhesion to ECs. The adhesion of BMCMCs to skin ECs is further enhanced by TNF, IL-4, IL-15 and vascular endothelial cell growth factor. Furthermore, BMCMCs exhibit directed and dose-dependent transmigration across an endothelial barrier, mediated by a PECAM-1-dependent mechanism. Our results demonstrate that BMCMCs can undergo a tightly regulated extravasation cascade consisting of rolling on and adhesion to endothelium and followed by directed diapedesis and reveal selectins, VCAM-1 and PECAM-1 as required adhesion molecules. These processes may contribute to mast cell accumulation in chronic inflammatory skin diseases and reveal opportunities to modulate peripheral tissue numbers of mast cells.

CD22 is a B cell-restricted transmembrane protein that apparently controls signal transduction thresholds initiated through the B cell Ag receptor (BCR) in response to Ag. However, it is still poorly understood how the expression of CD22 is regulated in B cells after their activation. Here we show that the expression levels of CD22 in conventional B-2 cells are markedly down-regulated after cross-linking of BCR with anti-IgM mAb but are up-regulated after stimulation with LPS, anti-CD40 mAb, or IL-4. In contrast, treatment with anti-IgM mAb barely modulated the expression levels of CD22 in CD5+ B-1 cells, consistent with a weak Ca2+ response in anti-IgM-treated CD5+ B-1 cells. Moreover, in CD22-deficient mice, anti-IgM treatment did not trigger enhanced Ca2+ influx in CD5+ B-1 cells, unlike CD22-deficient splenic B-2 cells, suggesting a relatively limited role of CD22 in BCR signaling in B-1 cells. In contrast, CD22 levels were markedly down-regulated on wild-type B-1 cells in response to LPS or unmethylated CpG-containing oligodeoxynucleotides. These data indicate that the expression and function of CD22 are differentially regulated in B-1 and conventional B-2 cells, which are apparently implicated in innate and adaptive immunity, respectively.

Triggering of the Fas/Fas ligand pathway leads to macrophage activation and to the induction of microbicidal activity in macrophages infected with Leishmania major. Upon infection with the protozoan parasite Leishmania major, susceptible BALB/c mice develop unhealing lesions associated with the maturation of CD4+Th2 cells secreting IL-4. In contrast, resistant C57BL/6 mice heal their lesions, because of expansion and secretion of IFN-γ of CD4+ Th1 cells. The Fas-FasL pathway, although not involved in Th cell differentiation, was reported to be necessary for complete resolution of lesions. We investigate here the role of IFN-γ and IL-4 on Fas-FasL nonapoptotic signaling events leading to the modulation of macrophage activation. We show that addition of FasL and IFN-γ to BMMø led to their increased activation, as reflected by enhanced secretion of TNF, IL-6, NO, and the induction of their microbicidal activity, resulting in the killing of intracellular L. major. In contrast, the presence of IL-4 decreased the synergy of IFN-γ/FasL significantly on macrophage activation and the killing of intracellular L. major. These results show that FasL synergizes with IFN-γ to activate macrophages and that the tight regulation by IFN-γ and/or IL-4 of the nonapoptotic signaling events triggered by the Fas-FasL pathway affects significantly the activation of macrophages to a microbicidal state and may thus contribute to the pathogenesis of L. major infection.