A4: an antigenic marker of neural tube-derived cells.

The A4 monoclonal antibody was originally found to bind to the surface of the majority of neurons in rat CNS cultures, but not to PNS neurons or non-neural cells. It was subsequently shown to bind to immature oligodendrocytes and their precursor cells but not to the most mature oligodendrocytes. In the present study, we have used immunofluorescence assays on cell suspensions and cultures and on semi-thin, frozen tissue sections to show that protoplasmic and fibrous astrocytes and most ependymal cells are also A4+. Taken together, these results suggest that in adult rats A4 is expressed exclusively by cells of the CNS and that all cell types derived from the neural tube are A4+, at least at some time in their development. While neurons, astrocytes and ependymal cells continue to express the antigen in adults, most oligodendrocytes appear to lose it as they mature. The finding that macrophages in CNS cell suspensions and cultures are A4- suggests that microglial cells are not derived from the neural tube.