Detection of biologically active TSLP in the sera of transgenic mice. (A) Sera from TSLP transgenic (TG) mice but not wild-type littermates (LM) stimulated the proliferation of the cytokine-dependent NAG 8/7 cell line. Results are given as the optical density (OD) ± SEM, which is directly proportional to amount of cellular proliferation. The OD for the negative control, cells incubated in medium only (not shown), was 0.211 ± 0.004. The results are representative of 3 independent experiments. Note: The mice used in these experiments were killed at 5 weeks of age. (B) Anti-TSLPR but not anti–IL-7 blocked NAG 8/7 cell proliferation induced by sera from TSLP transgenic mice (TG). Sera from littermate (LM) controls did not stimulate NAG 8/7 cell proliferation in the presence of either antibody. Results are given as the optical density (OD) ± SEM, which is directly proportional to amount of cellular proliferation. The results are representative of 2 independent experiments. Note: The mice used in these experiments were killed at 5 (LM 1.2 and TG 1.3), 2 (LM 2.3 and TG 2.4), and 7 weeks of age (LM 3.4 and TG 3.5).