Figure 3.

IL-5 (E12K) exhibits no agonist activity (A) and is a specific IL-5 antagonist (B) in a TF-1 cell proliferation assay. (A) TF-1 cells were incubated with increasing concentrations of either wild-type (open circles) or IL-5 (E12K) (closed circles) for 60–72 h and the induction of proliferation was measured using a nonradioactive cell proliferation assay. Each value represents the mean ± SEM of four independent experiments. (B) TF-1 cell proliferation was assayed at either 77 pM IL-5 (open circles), 133 pM IL-3 (closed squares) or 14 pM GM-CSF (closed triangles) in the presence of increasing concentrations of IL-5 (E12K). The concentrations of wild-type cytokines represent ∼ED₈₀'s (concentration of cytokine required to give 80% of the maximum biological response) for proliferation in our TF-1 cell line. Each value represents the mean ± SEM of six independent experiments. 100% values for IL-5–, IL-3–, and GM-CSF–induced proliferation were equivalent to A₅₅₀ of 0.68 ± 0.02, 0.73 ± 0.18, and 0.64 ± 0.04, respectively. Unstimulated levels were 0.03 ± 0.02.