Mast cell–deficient mice have increased amounts of Tcon survival/proliferation. Either WT C57BL/6 (H-2^b) or mast cell–deficient (C57BL/6-Kit^W-sh/Wsh) hosts were transplanted with 5.0 × 10⁶ TCD-BM, followed by 2.0 × 10⁶luc⁺ Tcon on day 4. Bioluminescent images were taken 10 days after transplant (A: in vivo imaging; B: ex vivo imaging). (C) C57BL/6-Kit^W-sh/Wsh mice demonstrated significantly more T-cell survival/proliferation than the corresponding C57BL/6 WT mice in lymph nodes, liver, and gut of Tcon (n = 5). Shown is 1 experiment of the 4 performed, each of which gave similar results.