The effect of SCIT on basophil activity. (a) Median LC50 is plotted against visit for patients on SCIT (n = 18). At visit 3 basophils are significantly more sensitive than at other visits. (b) The protective effect of plasma is illustrated by replacing plasma with serum from a non-allergic donor. (c) The net protective effect measured as change in LC50 between basophils activated in autologous serum and in heterologous plasma is larger in patients on maintenance dose (n = 9) than in patients initiating SCIT (n = 10).