A transient cell population could be detected during infection. (A) c-kit⁺/β7⁺ cells were present in the bone marrow and blood for 24 hours, day 5 after infection (upper right quadrant). These cells were absent in naive and day 6 infected mice. Bone marrow was gated on GHP. Blood ungated. ^*P < .05. (B) Gating on c-kit/β7⁺ cells (G1) showed that these cells in the blood and bone marrow have similar size (data taken from the same individual day 5 after infection). (C) The appearance of c-kit⁺/β7⁺ cells on day 5 (histogram) preceded the appearance of mature mast cells in the gut (line graph) by 3 days; n = 4. These data represent 1 of 3 separate experiments, and are expressed as means ± SD.