Early damage of sympathetic neurons after co-culture with macrophages

Since activated immune cells may damage peripheral nerves during inflammation, we developed a co-culture model that permits the direct study of macrophage-induced neuronal damage. Sympathetic neurons were enzymatically isolated from neonatal mice and co-cultured with increasing numbers of peritoneal macrophages for 24 h. This caused rapid neuronal cell death, reducing neuronal number by 24.1 +/- 4% with the addition of 11.5 x 10(3) macrophages, representing a ratio of 8 macrophages per neuron. Nuclear analysis showed that cell death occurred by both apoptosis and necrosis. These effects were not mimicked by addition of macrophage-conditioned medium, and were prevented by 10 microM dexamethasone. Although no appreciable neuronal death occurred beyond 24 h, the density of neurites was decreased between 1 and 2 days of co-culture (p < 0.05). There is, therefore, a rapid induction of cytotoxicity by macrophages after their addition to the neuronal cultures, followed by axonal damage without neuronal cell death.