Decreased growth of EL4 tumors in mast cell–deficient mice. (A) Cells (1 × 10⁶) of the murine T-cell lymphoma cell line EL4 were injected subcutaneously into the flanks of mast cell–deficient Mcpt5-Cre⁺/iDTR⁺ and C57BL/6 Kit^W-sh/W-sh mice as well as Mcpt5-Cre⁻/iDTR⁺ and WT C57BL/6 control mice and (left) tumor volume and (right) tumor area were assessed for 14 days using a Mitutoyo Quick Mini caliper. Data represent the mean ± SD of 4 to 6 tumors (n = 4, C57BL/6 Kit^W-sh/W-sh and WT C57BL/6 mice; n = 6, Mcpt5-Cre⁺/iDTR⁺ and Mcpt5-Cre⁻/iDTR⁺). When error bars are not shown, they were too small to be diagrammed. Statistical significance was assessed by 2-tailed Student t test. (B) WT C57BL/6, skin biopsy of EL4 tumor at day 14, magnification 100×. (C) Mcpt5-Cre⁻/iDTR⁺, EL4 tumor, magnification 100×. (D) Mcpt5-Cre⁺/iDTR⁺, EL4 tumor, magnification 100×. Toluidine blue staining, mast cells (purple), margin of tumor is marked with gray dotted line. Inserts show mast cells at 400× magnification. (E) WT C57BL/6, skin biopsy of EL4 tumor at day 14, magnification 100× (F) Mcpt5-Cre⁻/iDTR⁺, EL4 tumor, magnification 100× (G) Mcpt5-Cre⁺/iDTR⁺, EL4 tumor, magnification 100×, CD31 staining.