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

Objective and Design: The role of mast cells in spontaneous leukocyte rolli ng in venules of the mouse cremaster muscle and rat mesentery was investiga ted. Materials: The experiments were carried out using mast cell-deficient rats (Ws/Ws), WBB6F1 mice (W/W-v), and their congenic littermates (wild type). Treatment: Administration of compound 48/80 intraperitoneally (50 mu g) in rats and intrascrotally (5 mu g) in mice, 4h prior to the experiments. Methods: Intravital microscopy of the terminal vascular beds in mouse crema ster muscle and rat mesentery. Results: The level of spontaneous leukocyte rolling and the rolling velocit y in venules of mast cell-deficient animals exactly matched that seen in wi ld-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 spo ntaneous leukocyte rolling, at least not in rat and mouse microvessels.