Modulation of microglial form and immune function by factors released from goldfish optic nerves

Activation of microglia is associated with neural damage and may aid repair of the CNS. To begin to investigate their role, microglia purified from mouse brain were grown in media conditioned (CM) by goldfish optic nerve (GFON), optic tectum (GFOT), vagal lobe, telencephalon and cerebellum, and medium conditioned by rat optic nerves (RON). Microglia maintained in GFON- or GFOT-CM assumed an ameboid morphology, whereas microglia grown in media conditioned by the other neural tissues produced long, crenellated processes that resembled the ramified microglial form. Microglia maintained in all types of CM functioned as antigen presenting cells in a MHC-restricted manner when tested on conalbumin-specific Thelper (Th) cells, except for microglia maintained in GFON- and GFOT-CM. These studies suggest that GFON, in contrast to RON, produces a substance(s) that affects microglial morphology and immune reactivity, and may promote the vigorous regeneration seen in GFON after damage.