Immunohistochemical localization of vascular endothelial growth factor in the globule leukocyte mucosal mast cell of the rat respiratory and digestive tracts

Vascular endothelial growth factor (VEGF) is a potent angiogenic mitogen th at also increases vascular permeability. Immunohistochemical localization o f VEGF in the respiratory and digestive tracts of healthy adult rats was in vestigated at light and electron microscopic levels using a specific antibo dy. The results revealed solitary cells with strong VEGF immunoreactivity s cattered in the epithelium of the respiratory tract as well as in the lamin a propria and epithelium of the intestine. From ultrastructural features of their large cytoplasmic granules, VEGF-positive cells in the respiratory t ract were identified as globule leukocytes (GL). The immunoreactivity was l ocalized exclusively in the cytoplasmic granules of GL. Most of the VEGF-po sitive cells in the small intestine were located in the lamina propria, whe reas those in the large intestine were found more frequently in the epithel ium than in the lamina propria. They showed the same morphological features as respiratory tract GL and were identified as mucosal mast cells (MMC). W hen examined in serial sections, GL/MMC in the respiratory and digestive tr acts showed only weak reactivity to anti-histamine antibody. In contrast, c onnective tissue mast cells (CTMC), which were located in the submucosa of the digestive tract and in the connective tissues of the respiratory tract and other organs, were intensely immunopositive for histamine, whereas they showed no reactivity to anti-VEGF antibody. The specific occurrence of VEG F in GL/MMC suggests that this cell type is involved in paracrine regulatio n of the permeability of nearby microvessels, and that VEGF immunoreactivit y can be used as a histochemical marker to distinguish GL/MMC from CTMC.