IL6 and Alzheimer disease: Given that macrophages may be the most important source of IL-6 and IFN-γ, to investigate the mechanisms underlying the involvement of IL-18 in AD, we measured circulating IL-6 and IFN-γ levels and found that both the IL-6 and IFN-γ levels in the plasma were increased and positively associated with the IL-18 level in AD patients.