Spontaneous leukocyte rolling in rat and mouse microvessels is independent of mast cell activity

OBJECTIVE AND DESIGN: The role of mast cells in spontaneous leukocyte rolling in venules of the mouse cremaster muscle and rat mesentery was investigated. MATERIALS: The experiments were carried out using mast cell-deficient rats (Ws/Ws), WBB6F1 mice (W/Wv), and their congenic littermates (wild type). Treatment: Administration of compound 48/80 intraperitoneally (50 microg) in rats and intrascrotally (5 microg) in mice, 4 h prior to the experiments. METHODS: Intravital microscopy of the terminal vascular beds in mouse cremaster muscle and rat mesentery. RESULTS: The level of spontaneous leukocyte rolling and the rolling velocity in venules of mast cell-deficient animals exactly matched that seen in wild-type animals. Challenge with compound 48/80 markedly increased leukocyte adhesion and emigration in venules of wild-type animals. In contrast, the number of adherent and extravascular leukocytes was very low in compound 48/80-challenged animals lacking mast cells and did not differ from that seen in control animals treated with phosphate-buffered saline. CONCLUSIONS: The presence or activation of mast cells has no bearing on spontaneous leukocyte rolling, at least not in rat and mouse microvessels.