Quantification of the concentration of KitL in Schwann cell CM and the effect of pharmacologic or genetic inhibition of c-kit activity on mast cell migration to Schwann cell CM. (a) Concentration of murine KitL in WT, Nf1+/–, and Nf1–/– Schwann cell CM was determined by ELISA. Results represent the mean ± SEM of five independent collections from five independent Schwann cell cultures. *P < 0.05 for Nf1–/– versus WT or Nf1–/– versus Nf1+/– by the Student’s paired t test. (b) WT and Nf1+/– mast cells (2 × 105) were preincubated with a neutralizing Ab to the c-kit RTK, and haptotaxis assays were performed to either WT or Nf1–/– Schwann cell CM. Results represent the mean ± SEM of five independent experiments. *P < 0.05 for WT mast cell migration in response to WT or Nf1–/– Schwann cell CM in the presence or absence of the c-kit–neutralizing Ab. **P < 0.05 for Nf1+/– mast cell migration in response to WT or Nf1–/– Schwann cell CM in the presence or absence of the c-kit–neutralizing Ab by the Student’s paired t test. (c) Haptotaxis of mast cells of the four Nf1 and W genotypes in response to either 2 × 105 WT or Nf1–/– Schwann cell CM. Results represent the mean ± SEM of five independent experiments. *P < 0.05 for W41/W41 versus WT mast cell migration in response to either WT or Nf1–/– Schwann cell CM. **P < 0.05 for Nf1+/–; W41/W41 versus Nf1+/– mast cell migration in response to either WT or Nf1–/– Schwann cell CM by the Student’s paired t test.