Figure 1. Alveolar macrophage (AM) proliferation is decreased in aged mice in association with elevated levels of PGE₂.

(A) Absolute numbers of AMs enumerated from BALF of young (6–8 wk old) and aged (18–22 wk old) mice (n = 20–22 mice). (B) Primary AMs isolated from young and aged mice were treated with mouse GM-CSF (10 ng/ml) and incubated for 5 d and subjected to CyQuant proliferation assay measuring total cellular DNA (n = 5 mice). (C) Expression of Cyclin B1 mRNA measured by RT-PCR in young and aged primary AMs treated with GM-CSF for 48 h (n = 3 separate experiments). (D-left panel) Schematic depicting young and aged BALF swap experiment. (D-right panel) Proliferation of young AMs incubated for 5 d in the presence of young or aged BALF, or medium alone, with or without GM-CSF (n = 5–9 mice). (E) Heat map of lipids that were elevated in BALF from both young (n = 4 mice) and aged (n = 3 mice) mice. (F) Levels of PGE₂ from young or aged BALF quantified by ELISA (n = 17–18 mice). (G) Pearson’s correlation analysis between AM numbers and PGE₂ levels in matched BALF samples from individual mice (n = 18 mice; 10 young, 8 aged). (A, B, C, D, E) Results in (B, C, D) are values expressed relative to those in unstimulated young AMs, and all data represent the mean ± SEM of the values indicated by individual symbols; ns, non-significant, *P < 0.05, **P < 0.01, ***P < 0.001; t test (A, E) or one-way ANOVA followed by Sidak’s test for multiple comparisons (B, C, D).