THE CARBOHYDRATE EPITOPE 3-FUCOSYL-N-ACETYLLACTOSAMINE IS REGION-SPECIFICALLY EXPRESSED IN ASTROCYTES OF THE RAT-BRAIN - LIGHT-MICROSCOPIC AND ELECTRON-MICROSCOPIC OBSERVATIONS

The carbohydrate epitope 3-fucosyl-N-acetyllactosamine (CD15) is invol ved in cell-to-cell recognition processes in various tissues. In the C NS of the adult rat, immunoreactivity for CD15 reveals a region-specif ic distribution pattern by light microscopy. In the present study we i nvestigated the ultrastructural localization of CD15 in the rat brain using preembedding immunocytochemical methods. In addition we studied CD15 expression in cultured astrocytes from optic nerves of Ii-day-old rats. In optic nerve sections, immunostaining was found on the surfac e of astrocytes at various contact sites, i.e. astrocyte-astrocyte, as trocyte-oligodendrocyte, astrocyte-axon myelin, and astrocyte-blood ve ssel contacts. Oligodendrocyte-oligodendrocyte contacts, however, were always negative. In the telencephalic cortex, CD15 immunoreactivity w as found in glial cell processes around synapses and in the cerebellar cortex in Bergmann glial cells. In astrocytes grown in serum-containi ng medium, CD15 was expressed on the surface of fibroblast-like glial fibrillary acidic protein-positive astrocytes, which were identified a s type 1 astrocytes as well as on process-bearing A2BS-positive cells, representing type 2 astrocytes. The present data support the assumpti on that in the adult rodent brain, CD15 is exclusively expressed by as trocytes. The in vivo distribution of this carbohydrate molecule on di stinct astroglial contact sites supports the notion that CD15 could ac t in cell-to-cell recognition processes.