Old GILZ KO mice develop a chronic B-cell lymphocytosis. (A-C) Number of cells in BM (A), spleen (B), and pLN (C) isolated from 13- to 19-month-old WT and gilz KO mice (n = 9/10). (D) Frequency (left) and number (right) of B220⁺ cells in PB isolated from 13- to 19-month-old WT and gilz KO mice (n = 9/10). (E) Frequency (left) and number (right) of B220⁺ cells in pLN isolated from 13- to 19-month-old WT and gilz KO mice (n = 9/10). (F) Frequency (left) and number (right) of B220⁺ cells in spleen isolated from 13- to 19-month-old WT and gilz KO mice (n = 9/10). (G) Frequency (left) and number (right) of B1a (B220loIgM⁺IgD^–CD43⁺CD5⁺) cells in spleen isolated from 13- to 19-month-old WT and gilz KO mice (n = 9/10). (H) Frequency (left) and number (right) of B1a cells in peritoneum (PC) isolated from 13- to 19-month-old WT and gilz KO mice (n = 9/10). (I) Frequency (left) and number (right) of B220⁺CD5⁺ cells in blood isolated from 13- to 19-month-old WT and gilz KO mice (n = 4). (J) Spleen histologic phenotype of 18-month-old WT and gilz KO mice assessed by hematoxylin and eosin (H&E) staining. Scale bars represent 100 µm; original magnification ×20. (K) Immunohistochemical analyses show that the number of CD45R/B220⁺ lymphocytes in spleen is increased in gilz KO compared with WT mice. Scale bars represent 100 µm; original magnification ×20.