CFU-IL-7 progenitor activity is undetectable in the bone marrow and spleen of TSLP transgenic mice. Pre-B lymphocyte CFUs were significantly reduced in the bone marrow (P = .01) but not the spleen (P = .578) from transgenic (TG) versus littermate (LM) mice (y-axis break is 19-40). The results are presented as the average numbers of CFU-IL-7 ± SEM from triplicate experiments (n = 2 and n = 3 for TG and LM animals, respectively).