Abstract
We observed highly aggressively proliferating immortalized (HAPI) cells growing in cultures that had been enriched for microglia. The cells were initially obtained from mixed glial cultures prepared from 3โdayโold rat brains. HAPI cells are typically round with few or no processes when cultured in 10% serum containing medium. As the percentage of serum in the medium is decreased, the HAPI cells have more processes. HAPI cells stain for the isolectin B4, OXโ42, and GLUT5, which are markers for microglial cells, but the cells do not immunolabel with A2B5, a marker of cells in the oligodendroglial cell lineage, or with the astrocyteโspecific marker, glial fibrillary aciidic protein (GFAP). In addition, HAPI cells are capable of phagocytosis. We conclude that HAPI cells are of microglia/macrophage lineage. Exposing HAPI cells to lipopolysaccharide (LPS) induces the mRNAs for tumor necrosis factorโฮฑ (TNFโฮฑ) and inducible nitric oxide synthase (iNOS). LPS exposure also induces secretion of TNFโฮฑ and production of nitric oxide (NO) in HAPI cells. Because activation of microglia is associated with an increase in iron accumulation and ferritin expression, we tested the hypothesis that iron status affects the production of TNFโฮฑ and NO. Our studies demonstrate that both iron chelation and iron loading diminished the LPSโinduced effect of TNFโฮฑ and NO. The results of this study indicate that HAPI cells possess the characteristics of microglia/brain macrophages, providing an alternative cell culture model for the study of microglia. In addition, we demonstrate that the activation of microglial cells could be modified by iron. GLIA 35:53โ62, 2001. ยฉ 2001 WileyโLiss, Inc.