ACTIVATION OF ADULT HUMAN-DERIVED MICROGLIA BY MYELIN PHAGOCYTOSIS IN-VITRO

The present study was designed to determine the extent to which cultur ed glial cells phagocytose normal central nervous system (CNS) myelin and CNS myelin opsonized with serum or purified antibody against myeli n basic protein (MBP). Glial cells studied were mixed cultures (consis ting of astrocyte, microglia, and oligodendrocytes) and enriched micro glia established from adult human brain specimens and enriched astrocy tes from fetal human brain. A human monocytic cell line, THP-1, was in cluded as a control. Uptake of I-125-labelled myelin was followed over a 24 hr time period. An assay of oxidative burst (30 min) and cytokin e bioassays measuring IL-1, IL-6, and tumor necrosis factor (TNF) prod uction (6-48 hr) were used to investigate short- and long-term activat ion of phagocytosing cells. Maximum myelin uptake by phagocytosing gli al cells occurred within 12-24 hr following myelin incubation. Opsoniz ation of myelin prior to the phagocytosis assay resulted in greater my elin uptake by mixed glial cell cultures, microglia, and THP-1 cells o ver that of nontreated myelin. The magnitude of myelin phagocytosis by astrocytes was considerably lower than microglia and THP-1, and was n ot affected by myelin opsonization. Within 30 min of myelin phagocytos is, microglia and THP-1 cells underwent oxidative burst; opsonization of myelin by purified anti-MBP IgG and heat-inactivated serum enhanced the microglial oxidative burst activity. Production of IL-1, TNF, and most markedly IL-6 by microglia was increased following 12-24 hr of m yelin ingestion. Our data demonstrate that myelin phagocytosis by adul t human-derived microglia occurs in vitro, is augmented when myelin is opsonized, and results in the activation of microglia as assessed by oxidative burst and cytokine production. (C) 1994 Wiley-Liss, Inc.