Mucins require SFKs in both leukocytes and platelets to stimulate secretion of cathepsin G. Leukocytes and platelets of the indicated genotype were incubated with mucins. After pelleting the cells, the concentration of cathepsin G was measured using an enzymatic assay. Activity in control buffer-treated samples was subtracted as background. The data represent the mean ± SEM from 5 experiments. *P < .01.