Table 2. Alveolar macrophages recovered from old rats synthesize less TNF-α than those recovered from young rats.

Treatment	TNF-α (pg/ml)	MCP-1 (ng/ml)
Basal release from young rats	526 ± 153	1·5 ± 0·2
LPS-treated release from young rats	30542 ± 4661**	4·3 ± 0·1**
Basal release from old rats	325 ± 49	1·6 ± 0·2
LPS-treated release from old rats	9094 ± 2430**§§	4·5 ± 1·0**

TNF-α, tumour necrosis factor-α; MCP-1, monocyte chemotactic protein-1; LPS, lipopolysaccharide.

TNF-α produced by alveolar macrophages obtained from old rats was significantly reduced compared with alveolar macrophages obtained from young rats. Alveolar macrophages were treated for 24 hr in the absence (basal) or presence of LPS (100 ng/ml). Cytokine levels in conditioned media were assessed by commercially available enzyme-linked immunosorbent assay (ELISA) (MCP-1) and by specific bioassay (TNF-α). Data are mean ± standard error of mean (SEM) for four independent samples. The Bonferroni multiple comparison test was performed, with

^**P < 0·01 vs. basal release from alveolar macrophages and

^§§P < 0·01 vs. alveolar macrophages obtained from young animals.