A suppressive role of nitric oxide in MIP‐2 production by macrophages upon coculturing with apoptotic cells

Macrophages phagocytose apoptotic cells without causing neutrophil infiltration in vivo under physiological conditions. Our recent study, however, showed that macrophages produce IL‐8 or MIP‐2, a murine IL‐8 homologue, upon coculturing with apoptotic cells, indicating that there must be unknown mechanisms for preventing IL‐8 or MIP‐2 production. As activated macrophages produce NO to regulate inflammation, we examined the NO production by macrophages upon coculturing with apoptotic or necrotic cells and explored the role of NO in MIP‐2 production. NO was produced on coculturing with early apoptotic cells much more significantly than with late apoptotic or necrotic cells. On the contrary, MIP‐2 was produced on coculturing with late apoptotic or necrotic cells much more significantly than with early apoptotic cells. N G ‐Nitro‐ l ‐arginine methyl ester, an inhibitor of NO synthase, or 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide, a scavenger of NO, augmented MIP‐2 production on coculturing with early apoptotic cells. The addition of N‐ethylethanamine:1,1‐diethyl‐2‐hydroxy‐2‐nitrosohydrazine [1:1], a donor of NO, conversely, caused suppression of MIP‐2 production on coculturing with late apoptotic cells. These results suggest an important role of NO for preventing MIP‐2 production by macrophages upon coculturing with early apoptotic cells.