Lung macrophages are relatively deficient in young but not adult Op/Op mice.

Lung macrophages were visualized in young and adult Op/Op and control mice by using immunohistochemical staining for Mac-3 antigen (A-D) and quantified by morphometric analysis (E-F). Mac-3 staining of lung macrophages was strong and uniform in Op/Op mice aged 20 days (A) and 120 days (C) and in age-matched littermate controls (B,D). (E) Morphometric analysis showed a relative deficiency of lung macrophages in young Op/Op mice compared with controls (n = 6/group; age, 20 days; P < .001). (F) In contrast, numbers of lung macrophages were similar in adult Op/Op mice and controls (n = 11/group; mean age, 165.2 ± 10.3 versus 161.5 ± 9.1 days; P = 0.68; F). In control mice, Mac-3⁺cell numbers declined with age (P < .0001), whereas in Op/Op mice, they did not (P > .21) (× 100; insets, × 700).