Recently, we derived immortalized cells (HAPI) from primary microglia enriched cultures isolated from neonatal rat brain (P3). HAPI cells acquire the morphology of phagocytic macrophages and can be labeled with a microglial marker Isolectin B4. A double-labeled fluorescence of Isolectin B4 with oligodendroglial or astroglial markers demonstrated that HAPI cells belong to the microglia/macrophage lineage. Treatment with LPS (1μg/ml) induced transcript expression of inducible nitric oxide synthase and tumor necrosis factor (TNF)α assayed by RT-PCR. LPS induced the production of nitric oxide measured by colorimetric assay using Griess reagent. An ELISA indicated that LPS induced the secretion of TNFα from HAPI cells. These results demonstrated that HAPI cells possess the characteristics of rat microglia/brain macrophages (SFN'99, Abstract # 203.7). To further investigate the use of HAPI cells as a rat model to study neuroinflammation, we are using oligonucleotide microarrays to monitor changes in transcriptio...