Myeloid lineage cells inhibit neurite outgrowth through a myosin II-dependent mechanism.

The molecular mechanisms that underlie the axonal damage that accompanies CNS inflammation are largely unknown. Here, we investigate the effects of immune cells on neuronal viability and axonal growth and show that conditioned media from myeloid lineage cells inhibit neurite outgrowth without causing apoptosis. Treatment with monocyte conditioned medium enhances myosin light chain phosphorylation in neurons and the neurite outgrowth inhibitory effect of myeloid lineage cells can be attenuated with the myosin II inhibitor blebbistatin. Our results suggest that in the context of CNS inflammation myeloid cells may limit axonal repair in the CNS via a myosin II-dependent mechanism.