Expression of CD23 in response to IL-4/GM-CSF is accompanied by changes in huASMC morphology. Alpha-smooth muscle isoactin positive huASMC (Clonetics) in T-75 flasks were starved for 24 h in 0.1% FBS containing medium M199. The cells were then stimulated with either BSA or IL-4 (0.5 nM)/GM-CSF (0.4 nM) for 24 h, and stained with either anti-smooth muscle-isoactin (A & B) or anti-CD23 antibody (C & D). Those cells stimulated with the combination of IL-4/GM-CSF demonstrated CD23 expression (D) and changes in cell morphology including depolymerization of isoactin fibers, cell spreading, and membrane ruffling (B). Cells stimulated with BSA (vehicle for IL-4/GM-CSF) alone did not increase the expression of CD23 (C) nor changes in phenotype (A). These findings were confirmed by three independent observers.