Secretion of TNF-α by macrophage cell lines in response to MSU crystals or zymosan. TNF-α as measured by ELISA in culture supernatants collected from five phagocytically competent macrophage cell lines cultured for 16 hours in the presence of media alone, MSU crystals (0.5 mg/ml), or unopsonized zymosan particles (400 g/ml). Note that the mature macrophage cell lines IC-21 and MH-S secreted TNF-α in response to zymosan but not to MSU crystals. All these cell lines efficiently phagocytosed MSU crystals. Values are means ± SD of triplicates. (Reproduced from , with kind permission from Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc.).