Differential expression of CD44 splice variants in the normal human central nervous system.
Cluster of differentiation 44 (CD44) is a broadly distributed group of glycoproteins that are involved in many functions related to cell-cell and cell-matrix interactions. In the present study, the expression of the standard form of CD44 (CD44s) and of CD44 variants (CD44v) was explored immunohistochemically on frozen sections of various areas of the human CNS. The results demonstrate that CD44s epitopes are expressed predominantly by white matter astrocytes, whereas different CD44 variant molecules are present in neurons, on axonal membranes, on endothelium or on choroid plexus epithelium. Interestingly, neurons and axons differentially expressed CD44 variant epitopes but consistently lack immunoreactivity for CD44s epitopes. Another interesting finding was that some CD44 variant epitopes expressed by neurons were localized in the cytoplasm instead of on the cell membrane. The broad distribution of variant CD44 molecules in the human CNS suggests that CD44 may play an important role in many biological processes in the CNS.