THE HETEROGENEOUS DISTRIBUTION OF BRAIN TRANSFERRIN

Immunocytochemistry with antisera to transferrin has often been used t o identify oligodendroglia in tissue sections and cultures, but reacti on product also occurs in blood vessel walls and nerve cells. There is considerable species variation. Serum transferrin is largely biosynth esized in the liver, and its established physiological role is the tra nsport of iron to tissue sites and delivery of the metal to the interi or of cells that have transferrin receptors on their surfaces. In sect ions of the central nervous system, the visualization of iron and tran sferrin generally does not coincide, and transferrin may have importan ce to normal brain function beyond iron transport. For a comparative a nalysis of transferrin in rabbit and rat brain, polyclonal antisera we re raised against purified serum transferrins of these species. The an tisera were used for transferrin immunocytochemistry on vibratome sect ions and for immunochemical detection on electroblots. Transferrin imm unocytochemistry and iron histochemistry were compared. The electropho retic separation of brain extracts and transfer to nitrocellulose memb ranes permitted the quantitation of the protein and the study of the c arbohydrate chains of tissue-bound transferrins by biotinylated lectin s. An unexpected result in the rabbit was the dense immunocytochemical reaction product in Bergmann glia and Golgi epithelial cells. Reactio n in the cytoplasm of oligodendrocytes was relatively faint in this sp ecies except for some selected white matter tracts, e.g. the inferior cerebellar peduncles. In sections of rat brain, oligodendrocytes and v essel wails reacted vigorously in ail locations. Transferrin levels in rat brain were substantially higher than in rabbit brain. In the rabb it, maximum transferrin levels occurred in the cerebellum. The combina tion of lectin affinity chemistry and digestion with neuraminidase rev ealed the presence of sialylated, mannose-containing, and fucosylated intracellular brain transferrin in both species. These observations ma y also be relevant to the recently described neurological syndrome tha t is associated with carbohydrate deficiency of serum and cerebrospina l fluid transferrin.