Patterns of response to DNA damage in CLL. The histograms show the levels for p53 (A) and p21 (B). Black line, isotype control; dark gray line, nonirradiated sample; light gray line, irradiated sample. Normal response: low basal levels of p53 and p21 and induction of both proteins after irradiation. Type-A defect: high basal p53 level and impaired p21 induction. Type-B defect: low basal p53 level and impaired p21 induction.