Eotaxin influences mast cell differentiation in FBL. Graph A shows the percentage of more differentiated mast cells identified on cytospins stained with modified giemsa (MG), based on granular content. The percentage of heavily-granulated cells (toluidine blue (TB)⁺, MG⁺, or CAE⁺) was determined by counting the number of these cells (in 25 or 100 fields at 400× magnification) on cytospun preparations made by harvesting all colony progeny induced in methylcellulose. Total cell counts ranged from 84 to 964. (B) Increased numbers of TB⁺ mast cells are induced as the concentration of SCF increases. The patterned bar represents the percentage of TB⁺ cells induced with SCF alone (at 100 ng/mL). Because no TB⁺ cells were seen with SCF alone at 20 and 50 ng/mL, the patterned bar is prepresented by (0). The solid bar shows the percentage of TB⁺ cells induced with eotaxin (50 ng/mL) combined with increasing concentrations of SCF. (C and D) Mature mast cells generated after 10 days in culture with eotaxin and SCF are shown stained with TB or MG.