Peritoneal and skin mast cells in Kit mutant mice. Peritoneal exudate cells (PECs) (A-P) and skin (Q-T) from Kit^+/+ (A,E,I,M,Q), Kit^W/Wv (B,F,J,N,R), R⁻γ⁻Kit^W/Wv (C,G,K,O,S), and Kit^W/W (D,H,L,P,T) mice were analyzed for the presence of mast cells. PEC cytospins were stained with toluidine blue (A-D) and berberine sulfate (E-H). Absence of mast cells in all Kit mutants is evident by lack of staining with these dyes. Scale bars in A and E correspond to 60 μm. (I-L) Flow cytometric analysis of PECs for expression of the mast cell markers T1 and FcϵRI. T1⁺FcϵRI⁺ cells were absent in all Kit mutants. Cells on the diagonal, present in all plots, are myeloid cells that are unaffected by mutations in Rag-2, γ_c, or Kit. Cells on the bottom of the dot plots are lymphocytes that are absent in R⁻γ⁻Kit^W/Wv owing to the mutations in Rag-2, and γ_c (M-T). Mice were 12 to 13 weeks of age. RT-PCR analysis for expression of mast cell carboxypeptidase A (Mc-cpa), a mast cell–specific gene, as a sensitive tool to detect mast cells in PECs (M-P) and ear skin (Q-T). The triangles indicate 5 cDNA dilutions in 1:10 steps. In line with the analysis shown in panels A through L, PECs lacked Mc-cpa expression in all Kit mutants (N-P). In contrast, Mc-cpa expression was detectable in Kit^W/Wv (R) and R⁻γ⁻Kit^W/Wv (S) mice. This expression was 10- to 100-fold reduced compared with Kit^+/+ skin (Q). Mc-cpa expression was undetectable in the skin of Kit^W/W mice (T). Mice were 24 weeks (Kit^+/+ [C57BL/6]), 12 weeks (Kit^W/Wv), 31 weeks (R⁻γ⁻Kit^W/Wv), and 17 weeks (Kit^W/W) old.