Distribution of the carbohydrate epitope 3-fucosyl-N-acetyl-lactosamine (FAL) in the adult human brain.

The distribution of the carbohydrate epitope 3-fucosyl-N-acetyl-lactosamine was investigated on paraffin sections of the normal adult human central nervous system by means of immunohistochemistry, using the mouse monoclonal antibody anti-Leu-M1. This antibody is one among many others recognizing this epitope, which is also known as stage specific embryonic antigen I or X-hapten. We found this epitope predominantly localized on astrocytes especially along their numerous cell processes. There was a striking association of immunoreactive astrocytes with intracortical blood vessels and with distinct brain areas. Leu-M1-positive oligodendrocytes were present in the white matter with highest densities in the centrum semiovale and lateral pontine regions. Most cells of the ependymal lining, including tanycytes, showed Leu-M1 immunoreactivity but there was some topographical variability. Double-labelling experiments revealed that Leu-M1-positive glial cells may or may not be immunoreactive to glial fibrillary acidic protein or S-100 protein. The Leu-M1 antibody also stained a large number of different sets of neurons from cerebral cortex to spinal cord. Groups of immunostained cells were found in the hypothalamus, dorsal thalamus, ventral and mesial mesencephalic tegmentum, and several lower brainstem regions such as the lateral reticular formation, the raphe nuclei and the pons. Leu-M1 immunoreactivity appeared associated to neurochemically specified neuronal cell groups such as the mesencephalic dopaminergic system and the hypothalamic neurophysin system. In summary, our study demonstrates a distinct topographical distribution of the Leu-M1 epitope in the adult human central nervous system. Its exact functions, however, have not yet been elucidated, but there is evidence for the involvement of this epitope in cell-cell-adhesion and -interaction processes.