Ik^−/− mice exhibit reduced intestinal mast cell numbers. (A) Mast cells (arrows) were identified in Ik^−/− mice and their wild-type littermates by toluidine blue staining of sections from ear skin and intestine (original magnification ×40; Zeiss Primo Star with ImagingSource digital camera attachment). (B) Quantification of mast cell numbers in skin and intestine tissue samples. Each data point represents the average number of mast cells observed in an individual mouse counting 4 sections and 5 fields/section. (C) Numbers of MCps in Ik^+/+ and Ik^−/− mice were assessed by limiting dilution analysis of intestinal mononuclear cells (MNC) in medium containing IL-3 and SCF. Data represents mean MCps from 4 individual mice/group ± standard error of the mean and are representative of 2 independent experiments. *P < .05; ** P < .01.