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Rationale: As the smallest free-living bacteria and a frequent cause of respiratory infections, mycoplasmas are unique pathogens. Mice infected with Mycoplasma pulmonis can develop localized, life-long airway infection accompanied by persistent inflammation and remodeling.Objective: Because mast cells protect mice from acute septic peritonitis and gram-negative pneumonia, we hypothesized that they defend against mycoplasma infection. This study tests this hypothesis using mast cell-deficient mice.Methods: Responses to airway infection with M. pulmonis were compared in wild-type and mast cell-deficient Kit(W-sh)/Kit(W-sh) mice and sham-infected control mice.Measurements and Main Results: Endpoints include mortality, body and lymph node weight, mycoplasma antibody titer, and lung mycoplasma burden and histopathology at intervals after infection. The results reveal that infected Kit(W-sh)/Kit(W-sh) mice, compared with other groups, lose more weight and are more likely to die. Live mycoplasma burden is greater in Kit(W-sh)/Kit(W-sh) than in wild-type mice at early time points. Four days after infection, the difference is 162-fold. Titers of mycoplasma-specific IgM and IgA appear earlier and rise higher in Kit(W-sh)/Kit(W-sh) mice, but antibody responses to heat-killed mycoplasma are not different compared with wild-type mice. Infected Kit(W-sh)/Kit(W-sh) mice develop larger bronchial lymph nodes and progressive pneumonia and airway occlusion with neutrophil-rich exudates, accompanied by angiogenesis and lymphangiogenesis. In wild-type mice, pneumonia and exudates are less severe, quicker to resolve, and are not associated with increased angiogenesis.Conclusions: These findings suggest that mast cells are important for innate immune containment of and recovery from respiratory mycoplasma infection. [ABSTRACT FROM AUTHOR]

Mast cell-deficientKit W/ Kit W-v mice are an important resource for studying mast cell functionsin vivo. However, because they are compound heterozygotes in a mixed genetic background and are infertile, they cannot be crossed easily with other mice.To overcome this limitation, we explored the use ofKit W-sh/ Kit W-sh mice for studying mast cell biologyin vivo.These mice are in a C57BL/6 background, are fertile and can be bred directly with other genetically modified mice. Ten-week-oldKit W-sh/ Kit W-sh are profoundly mast cell-deficient. No mast cells are detected in any major organ, including the lung. Gene microarrays detect differential expression of just seven of 16 463 genes in lungs ofKit W-sh/ Kit W-sh mice compared with wild-type mice, indicating that resting mast cells regulate expression of a small set of genes in the normal lung. Injecting 107 bone marrow-derived mast cells (BMMC) into tail veins ofKit W-sh/ Kit W-sh mice reconstitutes mast cell populations in lung, stomach, liver, inguinal lymph nodes, and spleen, but not in the tongue, trachea or skin. Injection of BMMC into ear dermis or peritoneum reconstitutes mast cells locally in these tissues. When splenectomizedKit W-sh/ Kit W-sh mice are intravenously injected with BMMC, mast cells circulate longer and are found more often in the liver and inguinal lymph nodes, indicating that the spleen acts as a reservoir for mast cells following injection and limits migration to some tissues.In summary, these findings show that mast cell-deficientKit W-sh/ Kit W-sh mice possess unique attributes that favour their use for studying mast cell functionsin vivo. [ABSTRACT FROM AUTHOR]

Inflammatory stimuli cause plasma leakage and leukocyte adhesion in venules but not in capillaries or arterioles. The specific response of venules is governed by phenotypic specialization of the venular endothelial cells. What regulates this specialized phenotype? Several recent developments have shed new light on this question and may challenge our thinking about regulation of the venular endothelial cell phenotype. In this review, we consider some of the molecular markers of venular endothelial cells, the hemodynamic and molecular factors that may regulate the phenotype of venular endothelial cells, and abnormalities in endothelial cell phenotype in disease-related angiogenesis and microvascular remodeling. The expanding list of molecular markers may help clarify the physiologic and molecular factors that regulate the phenotype of venular endothelial cells in normal development and disease. [ABSTRACT FROM AUTHOR]

Objective: In 1961, Majno and Palade proposed that plasma leakage in acute inflammation caused by histamine, serotonin, or bradykinin results via gaps that form between endothelial cells of postcapillary venules. Now the relevance of endothelial gaps in plasma leakage is being questioned. The purpose of this review is to summarize experimental evidence from our studies showing that endothelial gaps participate in plasma leakage in inflammation. Methods: Using neurogenic inflammation as a model of plasma leakage in acute inflammation, we compared five methods to determine whether endothelial gaps form in the microvasculature of the rat trachea. 1) Endothelial cell borders and gaps were stained with silver nitrate and visualized by light, scanning, and transmission electron microscopy. 2) The luminal surface of endothelial cells was examined by scanning electron microscopy. 3) The luminal surface of endothelial cells was stained with a biotinylated lectin and avidin-biotin-peroxidase histochemistry, and then was examined by differential interference contrast microscopy. 4) Endothelial junctions were reconstructed from serial sections photographed by transmission electron microscopy. 5) Leakage was measured after perfusion of lectins or tracers through aldehyde-fixed vessels in situ. Results: The results from the five methods used in this system were consistent with the formation of gaps between endothelial cells. Endothelial gaps were rare or absent under baseline conditions, but appeared with the onset of plasma leakage and had a distribution that matched the distribution of leakage. Gaps had a complex morphology and were accompanied by fingerlike cell processes, which may anchor adjacent endothelial cells to one another and participate in gap closure. In contrast to normal vessels, vessels that were leaky in life continued to leak after aldehyde fixation, in evidence that, once formed, the leakage pathway did not require energy-dependent membrane movement or... [ABSTRACT FROM AUTHOR]