MYELIN BASIC-PROTEIN IMMUNOREACTIVITY IN THE HUMAN EMBRYONIC CNS

Myelin basic protein (MBP) is a major myelin constituent produced by o ligodendrocytes in the central nervous system (CNS). Expression of MBP was considered to be a marker for oligodendrocyte differentiation and myelination in the developing CNS. In this study, expression of myeli n basic protein (MBP) and its messenger RNA (mRNA) was examined in hum an embryos and fetuses ranging in age from 5 to 20 gestational weeks ( g.w.). We were able to demonstrate that MBP antibody labels cells in b oth human nervous and non-nervous tissues beginning from early embryon ic life (5-6 g.w.). MBP positive (MBP +) cells were rounded, with eith er no cell processes or only 1-2 short processes, and were located in caudal regions of the CNS. MBP + cells were also observed in the non-n ervous tissue, such as leptomeninges, choroid plexus, and connective t issues. A number of MBP + cells in nervous and non-nervous tissues wer e morphologically similar to macrophages and showed a positive reactio n to macrophage-microglia markers: lectin (RCA-1) and the monoclonal a ntibody (EBM-11) to human macrophage antigen CD68, whereas they were n egative for neuronal, astroglial, or marker for oligodendrocyte progen itors. At the same embryonic age, 5 g.w. and onward, the MBP mRNA was observed in the CNS by in situ hybridization. The results of this stud y show that MBP immune reaction is spread in a large area of the CNS p rior to myelin appearance. In addition, for the first time it has been demonstrated that the same population of cells could be labelled with both MBP and macrophage markers. These results indicate that MBP, or MBP-related proteins, could represent a link between the immune and ne rvous system during early development. Thus, besides the well establis hed role in myelination, these proteins might have an additional and s till unknown function in development. (C) 1998 Elsevier Science B.V.