FIGURE 8.

Model for the effects of diminished or absent Lyn kinase activity on mast cell regulation. Top, Hypothetical curves are shown for positive and negative regulatory functions of Lyn. Middle, Low-intensity stimulation of FcεRI (upper panel) leads to weak activation of SFKs. This is insufficient to generate an appreciable biological response (y-axis) in Lyn-deficient cells. Lyn is the predominant SFK in mast cells, and the minor activity associated with the Lyn^WeeB allele, combined with other SFKs, is sufficient for a maximal response in many cases. This suggests a sharply ascending peak as the kinase activity generated by a given stimulus increases. Bottom, The majority of SFK capacity, used during high-intensity stimulation of FcεRI, leads to increasing negative regulation in wt and WeeB cells; biological activity in lyn^−/− cells still remains on the ascending region of the curve under these conditions. This simplified model does not take into account potential differences in function for the different SFKs present in mast cells. Note that the reduction in total SFK capacity for lyn^−/− and WeeB mast cells from wt levels is far greater than that depicted.