Macrophages/microglial cells in human central nervous system during development: an immunohistochemical study

The development of microglia and macrophages was studied in 14 human embryo s and fetuses ranging in age from 4.5-13.5 gestational weeks (g.w.), using lectins, Ricinus communis agglutinin-1 [RCA-1], and Lycopersicon esculentum , tomato lectin (TL), which recognize macrophages and microglia, and antibo dies for the macrophage antigen CD68. Lectin-positive (+) cells were observ ed at 4.5 g.w,, the youngest age examined. They were detected in the leptom eninges around the neural tube, and only rarely were observed in the CNS pa renchyma. At 5.5 g,w., lectin + cells were present throughout the CNS paren chyma, and a portion of these cells could also be labeled with antibody to CD68. In subsequent weeks, both types of cells, lectin + and CD68 + /lectin + cells co-existed and progressively developed typical microglial morpholo gy. In addition, in double label experiments, an antibody that labels CD14 antigen present on monocytes, hematogenous precursors of tissue macrophages , did not label either lectin + or CD68 + /lectin + cells in CNS parenchyma . Additional immunocytochemical studies with appropriate markers excluded t he possibility that any of the cells described here were either astrocytes, oligodendrocytes, endothelial cells or neurons. Our finding that one class of cells can be labeled early only with lectins, while another can be labe led with both lectins and CD68 macrophage antibody, may reflect a different origin of microglia in the early embryonic CNS compared to the fetal stage s. This subdivision appears to be maintained in the adult brains as well. ( C) 1998 Elsevier Science B.V. All rights reserved.