Increased IFN-mediated STAT3 phosphorylation and proliferation in ATM^−/− cell lines. (A) GM16667 (wt ATM) and GM16666 (absent ATM) cells in exponential growth phase were treated with IFN-α2b (1000 U/mL) for the indicated times, and whole cell lysates were then immunoblotted with antibodies to phosphotyrosine 701-specific STAT1, phosphotyrosine 705-specific STAT3, total STAT1 and STAT3, or β-actin. (B) After 3 days of culture, the cells were stained and images were taken at a magnification of ×10. Pictures were taken with a Canon PowerShot G11 Digital Camera equipped with a Carl Zeiss 426126 lens. The microscope was an Axiovert 40 C equipped with an A-plan 10×/0.25 objective, both from Zeiss. (C) The cells were also counted manually in a hemocytometer. The average (+ SE) of 3 separate measurements is shown and the experiment was performed twice with similar results. *P < .01; **P < .05