Figure 1.

Internalization of chimeric receptors. Individual clones were cultured as described in MATERIALS AND METHODS and incubated with 100 pM radiolabeled GM-CSF for 2 h at 4°C. Unbound ligand was removed, and cells were placed at 37°C for the indicated times. Surface-bound ligand was stripped by washes with PBS, pH 3.0, and radioactivity was measured. The remaining cell pellet was solublized and measured as internalized ligand. Each curve for each clone represents the mean ± SEM of two (A105), three (A122), or four (A120 or A110) independent experiments assayed in duplicate. The specific endocytotic rate constant (k_e) was determined for each of the clones over the first four data points (A105, 0.01/min; A110, 0.02/min; A120, 0.02/min; A122, 0.01/min). Analysis of variance shows no statistical difference between the rates (p > 0.60). The initial and maximal percent internalization, respectively, for clone A105 was 10.6% and 53.0%, for clone A110 was 7.5% and 51.9%, for clone A120 was 6.3% and 42.9%, and for clone A122 was 5.3% and 43.0%.