Delayed progression of the cell cycle during proliferation of peripheral lymphocytes. (A) Mitogen-induced proliferation of splenocytes of wild-type (WT, n = 4) and APEX2-null (KO, n = 4) mice. Splenocytes were stimulated with LPS or ConA, and numbers of viable cells were counted under a microscope. Mean values ± SD are indicated. ○ indicates WT; ▴, KO. Solid lines represent cells incubated with mitogens; dotted lines indicate that no stimulant was used. ^**P < .01. ^*P < .05. (B) Cell cycle distribution of proliferating splenocytes. DNA contents of isolated nuclei stained with propidium iodide were analyzed by flow cytometry. Distribution of isolated nuclei in each cell cycle phase is shown as a percentage ± SD. Open columns indicate WT (n = 7); closed columns, KO mice (n = 10). ^**P < .01. ^*P < .05. (C) Induction of APEX2 expression by stimulation with LPS or ConA for 48 hours. APEX2 protein in whole-cell extracts of splenocytes from WT and KO mice was detected by Western blotting using anti-APEX2, as indicated by the arrowhead.