Subpopulations of human fetal cortical microglia express markers IBA1 and HAM56

Abstract

Microglia are resident mononuclear phagocytes of the central nervous system (CNS), which regulate postnatal normal brain function. Under physiological conditions they actively survey their cell-specific territory with fine elongated processes, while in response to pathological stimuli they can transform into an activated amoeboid for. Microglia act as sentinels, detecting the slightest signs of tissue invasion or damage, capable of phagocytosing both neuronal debris and foreign agents. Recently, microglial functions were extended to processes such as embryonic and adult neurogenesis as well as postnatal synapse formation.We evaluated the density and distribution of microglial cells marked by ionized calcium-binding adapter molecule 1 (IBA1), marker that labels nearly all microglial cells, in the dorsal and ventral telencephalon of human abortion cases aged 17-21 gestational weeks (GW). In particular, we studied whether there would be differences in the density of IBA1-labeled microglia in different germinative layers of the developing pallium. We found higher density in the subventricular zone (SVZ) as compared to the ventricular (VZ) or intermediate (IZ) zones of the dorsal pallium. The percentage of mitotically active microglia was highest in the outer subventricular (oSVZ) and marginal zonez (MZ).We assessed the relationship in expression between the microglial-specific marker Iba1 and Ham56, which labels blood-borne tissue-specific macrophages in the ventricular and inner subventricular zones in the developing human forebrain. Double labeling revealed a distinct subset of cells, positive for both markers, thus demonstrating the existence of IBA1+/HAM56+ and IBA1+/HAM56- subpopulations of microglia. Overall, our results show differential distribution of microglia in the germinative zones of developing human telencephalon, which opens a possibility of a differential regulation of the progenitor cells located in these zones.