Inflammatory mechanisms contribute to neurodegeneration in AD. Acute phase proteins such as the antichymotrypsin (a1ACT), pro-inflammatory cytokines IL-6 and IL-1, and activated microglial cells are all associated with neuritic plaques. a1ACT levels are elevated in AD, correlate with cognitive decline and serve as a biological marker of intervention. a1ACT is intimately associated with the 42-AA b peptide (Ab) in filamentous amyloid deposits and stimulates the polymerization of Ab into amyloid filaments. IL-6 is found in AD cortices prior to the onset of neuritic change, serum and stimulated PMNC IL-6 levels are higher in AD, and may induce b-amyloid protein deposition. Microglia, CNS resident inflammatory cells, produce IL-6 within the adult human brain, are IL-1a +, and are a prominent component of the neuritic plaque. Because the pathogenesis of AD appears in part immune mediated, we propose testing directly in humans whether ingested IFN-a can ameliorate AD. Because there is no good model for inflammation in animal models of AD, we will directly determine in humans 1) if 3,000 or 30,000 IU hrIFN-a inhibits the natural history rate of cognitive decline in mild to moderate AD using neuropsychological instruments as primary and secondary outcome measures that 2) correlates with inhibition of acute phase reactants and pro-inflammatory IL-6. If this novel anti-inflammatory agent inhibits the natural history rate of cognitive decline in AD in this pilot phase II trial, this would provide the preliminary data to submit a phase III clinical trial.