Age‐related microgliosis in Pen‐2 cKO mice. A, Representative images for fluorescence IHC on Iba1 in the cortex. Mice at 3, 6, and 9 mo were examined. Note that the immuno‐reactivity of Iba1 was not increased in Pen‐2 cKO mice at 3 mo compared with controls. Boxed areas in (a), (b), (e), and (f) were enlarged as (g), (h), (i), and (j), respectively. Scale bar is 200 μm for (a‐f) or 100 μm for (g‐j). B, Averaged number of Iba1+ cells in the cortex. There was significant difference between control (Con) and Pen‐2 cKO (cKO) mice at each age (3 mo: P > 0.2; 6 mo: **P < 0.01; 9 mo: ***P < 0.001; n = 3‐4 mice per group). C, Western analysis on Iba1. Note that Iba1 levels in Pen‐2 cKO (cKO) mice did not differ from those in controls (Con) at 3 mo of age but were increased at 6 and 9 mo (3 mo: not significant; 6 mo: *, P < 0.05; 9 mo: **P < 0.01; n = 3‐4 per group). D‐F, qPCR analyses for Iba1 (D), IL‐1β (E), and TNFα (F). Data for 6 and 9 mo were presented. There was significant increase on levels for Iba1 (D), IL‐1β (E), and TNFα (F) in Pen‐2 cKO (cKO) mice compared with controls (Con) at either age (***P < 0.001; n = 3‐4 per group)