Distribution of interleukin‐1‐immunoreactive microglia in cerebral cortical layers: implications for neuritic plaque formation in Alzheimer’s disease

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Abstract
Activated microglia overexpressing interleukin‐1 (IL‐1) are prominent neuropathological features of Alzheimer’s disease. We used computerized image analysis to determine the number of IL‐1α‐immunoreactive (IL‐1α+ ) microglia in cytoarchitectonic layers of parahippocampal gyrus (Brodmann’s area 28) of Alzheimer and control patients. For cortical layers I and II, the numbers of IL‐1α+ microglia were similar in Alzheimer and control patients. For layers III–VI, the numbers of IL‐1α+ microglia were higher than that seen in layers I–II for both Alzheimer and control patients. Moreover, for layers III–VI, the number of IL‐1α+ microglia in Alzheimer patients was significantly greater than that in control patients (relative Alzheimer values of threefold for layer III–V and twofold for layer VI; P+ microglia in Alzheimer patients correlated with the cortical laminar distribution of β‐amyloid precursor protein‐immunoreactive (β‐APP+ ) neuritic plaques found in Alzheimer patients (r=0.99, P+ microglia in control patients also correlated with the cortical laminar distribution of β‐APP+ neuritic plaques found in Alzheimer patients (r=0.91, P+ microglia (i.e. that seen in control patients) are important in determining the observed laminar distribution of β‐APP+ neuritic plaques in Alzheimer patients. These findings provide further support for our hypothesis that IL‐1 is a key driving force in neuritic plaque formation in Alzheimer’s disease.