HUMAN MICROGLIA CULTURES - A POWERFUL MODEL TO STUDY THEIR ORIGIN ANDIMMUNOREACTIVE CAPACITY

In this paper, we report that pure cultures of human microglia were ob tained from long-term astrocytic cultures of human fetal brain. After five to six months and repeated cell passages, macrophage-like cells s tarted to spontaneously form in vitro, so that in two to three weeks t he whole culture was populated by them. These cells were grown up to o ver 50 passages in culture and analyzed for morphology, specific marke r positivity, growth rate and major histocompatibility complex (MHC) a ntigen expression with or without gamma-interferon (IFN) stimulation. We found that, regardless of embryonic age of original cultures (10-15 weeks of gestation), cultures showed a remarkable homogeneity and pur ity and over 90 stained for typical microglial markers. Under basal co nditions, two cell subpopulations similar to those described in vivo, we observed: the reactive 'ameboid' type and the resting 'ramified' on e, the latter increasing with time in vitro and cell passages. Both ce ll subpopulations were capable of active phagocytosis and of high-rate proliferation. They spontaneously expressed low levels of MHC class I I antigens, but were negative for MHC class I. Stimulation with gamma- interferon lymphokine upregulated the MHC class II expression as well as the MHC class I heavy chain form in ameboid, 'reactive' cells but n ot in the ramified ones. We also found that beta(2) microglobulin, alr eady expressed in basal conditions, was dissociated from HLA A-B-C mol ecules in lymphokine-stimulated cells at early passages. The physiolog ical significance of these data, as well as the possible correlation w ith in vivo ontogenetic modifications, are also discussed.