Alzheimer's disease (AD) is a progressive neurodegenerative disorder, of which the pathogenesis is thought to involve increased beta-amyloid (Abeta) deposition and abnormal immunological responses. To elucidate the mechanisms involved in Abeta-mediated inflammation, we used immunocytochemistry and in situ hybridization to study the potential role of the cytokines interferon-gamma (IFN-gamma), interleukin (IL)-12 and IL-4 in transgenic mice APP(SWE) (Tg2576) that overexpress the human beta-amyloid precursor protein gene. Cytokine and cytokine mRNA expression was detected in brain sections from cortical regions at various postnatal ages ranging from 3 to 19 months. High levels of IFN-gamma and IL-12 mRNA expression, as well as their protein production, appeared early at 9 months and peaked at 17-19 months in Tg2576 mice. Significantly increased transcripts of IFN-gamma and IL-12 genes were found in the reactive microglia and astrocytes surrounding beta-amyloid deposits. In accordance with the kinetics of mRNA levels, the expression of IFN-gamma and IL-12 at the protein level was positively correlated with age and reached a maximum in 17-19-month-old mice. Both findings suggest a role for the pro-inflammatory cytokines IFN-gamma and IL-12 in early disease development and are consistent with microglial activation related to beta-amyloid formation. In contrast, transcription and production of IL-4 in brain sections was almost undetectable in transgenic mice up to post-natal ages of 17-19 months. These results suggest a major pro-inflammatory role for IL-12 and IFN-gamma in Tg2576 transgenic mice that may provide the association between beta-amyloid plaque formation and microglial and astrocyte activation in these animals. These observations call for further studies on the potential role of anti-inflammatory therapeutic strategies for AD.