Localization of microglia in the human fetal cervical spinal cord.

Differential morphologic subtypes of microglia have been identified in the human fetal frontal cerebrum using a lectin, Ricinus communis agglutinin 1 (RCA-1), and a monoclonal antibody, EBM-11. In this report, microglia were characterized in the human fetal cervical spinal cord. RCA-1-positive microglia were ramified in the developing gray matter while in the developing white matter they had a less differentiated (ameboid) appearance. EBM-11, a monoclonal antibody that recognizes CD68 on human macrophages, and microglia labeled only ameboid-type microglia in the developing white matter. This suggests that distinct subpopulations of microglia exist, which may represent different stages in microglial development, and that CD68 may be a differentiation marker for less mature forms. Therefore, cytologically less differentiated forms of microglia appear to be associated with myelination.