Mast cells (MCs) play critical roles in allergy and inflammation, yet their development remains controversial due to limitations posed by traditional animal models. The zebrafish provides a highly efficient system for studying vertebrate hematopoiesis. We have identified zebrafish MCs in the gill and intestine, which resemble their mammalian counterparts both structurally and functionally. Carboxypeptidase A5 (cpa5), a MCspecific enzyme, is expressed in zebrafish blood cells beginning at 24 hours post fertilization (hpf). At 28 hpf, colocalization is observed with pu.1, mpo, l-plastin, and lysozyme C, but not fms or cepb␣, identifying these early MCs as a distinct myeloid population arising from a common granulocyte/ monocyte progenitor. Morpholino "knockdown" studies demonstrate that transcription factors gata-2 and pu.1, but not gata-1 or fog-1, are necessary for early MC development. These studies validate the zebrafish as an in vivo tool for studying MC ontogeny and function with future capacity for modeling human MC diseases. (Blood. 2008;112:2969-2972) IntroductionMast cells (MCs) play central roles in allergic and inflammatory reactions. 1,2 Stimulation of cell-surface receptors, such as C-KIT and the high-affinity IgE receptor, 1,2 results in the release of mediators from cytoplasmic granules, including tryptase and histamine. 2 MC number and function are regulated by their development, proliferation, migration, and survival. 1 Barriers to understanding these processes include accessibility and imaging limitations posed by traditional animal models. The zebrafish has proven itself to be a robust and highly conserved model for studying vertebrate hematopoiesis. 3 Here, we provide the first evidence that the zebrafish possesses MC equivalents that share structural and functional characteristics with their mammalian counterparts. Furthermore, we demonstrate the utility of the zebrafish as an in vivo tool in dissecting the contribution of transcription factors to MC development. MethodsZebrafish were maintained, bred, and developmentally staged according to Westerfield. 4 Use of zebrafish in this study was approved by the Dalhousie University Animal Care Committee. Zebrafish gills and intestine were fixed in 10% neutral buffered formalin, and standard staining procedures were applied ( Figure 1A-F). Immunohistochemistry was facilitated by antigen retrieval ( Figure 1I,J). For electron microscopy, tissues were fixed overnight in 2% glutaraldehyde in 0.1 M caccodylate and postfixed in 1% osmium tetroxide. Thin sections (90 nm) were stained in 25% uranyl acetate in methanol and lead citrate.Bromophenol blue and 10 g compound 48/80 or saline were injected intraperitoneally, and blood was extracted by cardiac puncture after 2.5 minutes. Tryptase activity was measured in plasma spectrophotometrically at 415 nm by the release of p-nitroanilide from N-benzoyl-DL-argininep-nitroanilide (BAPNA), a tryptase substrate.Digoxogenin-or fluorescein isothiocyanate (FITC)-labeled antisense mRNA probes for zebrafish carboxypep...
Toll-like receptors (TLR) induce distinct patterns of host responses through myeloid differentiation factor 88 (MyD88)-dependent and/or -independent pathways, depending on the nature of the pathogen. Pseudomonas aeruginosa is a cause of serious lung infection in immunocompromised individuals and cystic fibrosis patients. The role of the TLR-MyD88 pathway in P. aeruginosainduced lung infection in vivo was examined in this study. MyD88؊/؊ mice demonstrated an impaired clearance of P. aeruginosa from the lung. Little or no neutrophil recruitment was observed in the airways of MyD88 ؊/؊ mice following P. aeruginosa lung infection. This observation was associated with a reduced production of inflammatory mediators that affect neutrophil recruitment, including macrophage-inflammatory protein-2, tumor necrosis factor, and interleukin-1 in the airways of MyD88 ؊/؊ mice. Similarly, MyD88 ؊/؊ mice showed inhibited NF-B activation in the lung following P. aeruginosa infection. Interestingly, P. aeruginosa infection induced a 7.5-fold increase of TLR2 mRNA expression in the lungs of MyD88 ؉/؉ mice. Furthermore, host responses to P. aeruginosa lung infection in TLR2 ؊/؊ and TLR4 mutant mice were partially inhibited compared with the responses of respective control mice. Taken together, our results indicate that the MyD88-dependent pathway is essential for the development of early host responses to P. aeruginosa infection, leading to the clearance of this bacterium, and that TLR2 and TLR4 are involved in this process.
Pseudomonas aeruginosa is an opportunistic bacterial pathogen which is the leading cause of morbidity and mortality among cystic fibrosis patients. Although P. aeruginosa is primarily considered an extacellular pathogen, recent reports have demonstrated that throughout the course of infection the bacterium acquires the ability to enter and reside within host cells. Normally intracellular pathogens are cleared through a process called autophagy which sequesters and degrades portions of the cytosol, including invading bacteria. However the role of autophagy in host defense against P. aeruginosa in vivo remains unknown. Understanding the role of autophagy during P. aeruginosa infection is of particular importance as mutations leading to cystic fibrosis have recently been shown to cause a blockade in the autophagy pathway, which could increase susceptibility to infection. Here we demonstrate that P. aeruginosa induces autophagy in mast cells, which have been recognized as sentinels in the host defense against bacterial infection. We further demonstrate that inhibition of autophagy through pharmacological means or protein knockdown inhibits clearance of intracellular P. aeruginosa in vitro, while pharmacologic induction of autophagy significantly increased bacterial clearance. Finally we find that pharmacological manipulation of autophagy in vivo effectively regulates bacterial clearance of P. aeruginosa from the lung. Together our results demonstrate that autophagy is required for an effective immune response against P. aeruginosa infection in vivo, and suggest that pharmacological interventions targeting the autophagy pathway could have considerable therapeutic potential in the treatment of P. aeruginosa lung infection.
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