Microglial interleukin-1 alpha expression in human head injury: correlations with neuronal and neuritic beta-amyloid precursor protein expression.

Activated microglia containing IL-1 alpha-immunoreactive (IL-1 alpha +) product were increased 3-fold in number in the acute phase following head injury, a risk factor for later development of Alzheimer's disease, and this increase was correlated with a 7-fold increase in the number of neurons with elevated beta-amyloid precursor protein (beta-APP) levels (R = 0.78; P < 0.05). Furthermore, clusters of beta-APP+ dystrophic neurites present in these patients were invariably associated with activated IL-1 alpha + microglia. These findings suggest that early overexpression of IL-1 alpha and beta-APP is a priming event for later neuropathological changes evident at end stages of Alzheimer's disease.