TNF-α and MIP-2 protein release after exposure of alveolar macrophages to PD, HPD, and polystyrene microspheres (MS) assayed with ELISA kits. Alveolar macrophages were incubated with 5, 25, 100, or 200 μg/ml dust for 4 h. (A) TNF-α release, (B) MIP-2-release. Values represent means ± SEM of six separate experiments performed in duplicate. *p < 0.05 compared with medium alone. #p < 0.05 compared with HPD.