Retinoic acid increases CD15 expression in immortalized rat astrocytes

We have studied the expression of the CD15 (3-fucosyl-N-acetyl-lactosamine) epitope on immortalized astroglial cells derived from embryonic (E 19/20) rat brain. Immortalization was achieved by pulse-treatment of primary culture with 5-azacytidine. Seventy-three permanent cell lines were established by repeated cell cloning. Clones expressing GFAP, A2B5, and vimentin were regarded as immature astrocytes. One of these clones expressing CD15 was selected for manipulation studies. Monoclonal antibody was used for immunocytochemical detection of CD15 epitope and in immunoblot analysis. CD15 expression was visible in about 20% of the cells and was associated with a special morphological appearance. In the presence of retinoic acid the proportion of CD15-positive cells increased in a time-dependent manner, reaching about 90% within four days. Again, this expression was associated with the formation of distinct morphological features, including immunoreactive perinuclear granula, tips of processes and contact sites. After treatment with neuraminidase, all cells showed CD15-positive immunoreaction, revealing the presence of the epitope masked by sialylation. Immunoblot patterns of glycoproteins from trypsinized and mechanically detached cell preparations suggest that proteins, carrying sialylated CD15, might represent intracellular precursors of extracellularly active molecules.