The isolation and culture of microglia-like cells from the goldfish brain

We have developed a method for isolating goldfish microglia. Cells were identified as microglia immunohistochemically with NN-2, a monoclonal antibody (MAb) raised against teleost retinal microglial cells, and by their phagocytic abilities. Morphological characterization of the cells identified round, phase-bright cells as well as flattened macrophage-like cells. Ramified cells were also seen but they were rare. Fusion of macrophage-like cells occurred in high density cultures and resulted in the formation of giant cells that disintegrated a few days later. Immunohistochemical studies demonstrated that virtually all of the cells in our cultures were NN-2+ and did not label with either antiGFAP (an astrocyte marker) or MAb 6D2 (an oligodendrocyte marker). Cells identified as microglia were intensely phagocytic and ingested latex microspheres, DiIAcLDL and goldfish myelin in vitro. In addition, we labelled microglial cells in vivo with intracranial injections of fluorescent dextran and found that microglia isolated from these animals contained the dextran and phagocytosed microspheres. We also studied the effect of myelin on microsphere uptake and compared the effect of myelin and opsonized myelin on the phagocytic activity of the cells. Our results showed a clear increase in the phagocytic activity of microglia when incubated with myelin, with an enhanced effect of opsonized myelin.