Figure 1.

Pro-T cells are undetectable in mice lacking c-kit and γ_c. Wild-type (c-kit⁺γ_c⁺) (A–C, F, and G) and c-kit⁻γ_c⁻ (D, E, and H) thymic cells were analyzed for expression of Thy-1 vs. c-kit (F), or Thy-1 vs. CD25 (G and H). In wild-type mice, c-kit⁺Thy-1^low (R2) and CD25⁺Thy-1⁺ (R3) pro-thymocytes were further defined by FSC/SSC gate R1 (A and B). More mature thymocytes (R4) are outside of R1 (C). Pro-thymocytes defined by these criteria are lacking in c-kit⁻γ_c⁻ mice (D, E, and H). Cells in the lower left area (dot plot in H) are thymic epithelial cells. The absence of c-kit⁺ progenitors cannot be demonstrated directly in c-kit-deficient mice because of lack of c-kit surface expression.