Macrophages in the peripheral nervous system and astroglia in the central nervous system of rat commonly express apolipoprotein E during development but differ in their response to injury.

Macrophages have been identified by immunocytochemical methods in rat sciatic nerve neonatal development expressing significant amounts of apolipoprotein E (apo E). In contrast, in mature peripheral nerve apo E appears to be associated with the basal lamina. Following sciatic nerve crush apo E-immunoreactive macrophages reappear in the denervated distal stump within 3 days. In the optic nerve and spinal cord of newborn rat apo E is associated with the astroglia. During maturation of the central nervous system the number of apo E-immunoreactive astrocytes significantly increases, but as a specific response to injury this protein rapidly disappears from the astroglial cell bodies.