We investigated whether lipid extract from a blue-green alga, N commune, modulates proinflammatory gene expression in RAW 264.7 macrophages. The cells were incubated with N commune lipid extract (0-100 microg/mL) and subsequently activated by LPS (100 ng/mL). Quantitative real-time PCR analysis showed that mRNA abundance of proinflammatory mediators, including TNF-alpha, COX-2, IL-1beta, IL-6, and iNOS, was significantly reduced by N commune lipid extract in a dose-dependent manner. Secretion of TNF-alpha and IL-1beta into cell culture medium was also significantly decreased by N commune lipid extract. Thin-layer chromatography-densitometry analysis showed that N commune lipid extract contained approximately 15% of fatty acids. To determine whether the inhibition of proinflammatory mediator production by N commune lipid extract is primarily conferred by fatty acids in the lipid extract, macrophages were incubated with 100 microg/mL of N commune lipid extract or 15 microg/mL of a fatty acid mixture, which was formulated to reflect the fatty acid composition of N commune lipid extract. The fatty acid mixture significantly reduced RNA abundance of TNF-alpha and COX-2, but to a lesser extent than did the N commune lipid extract, suggesting the presence of additional bioactive compounds with an antiinflammatory property in the lipid extract. As NF-kappaB is a major regulator for the proinflammatory gene expression, we measured its DNA-binding activity. DNA-binding activity of NF-kappaB was significantly reduced by N commune lipid extract. In conclusion, our study suggests that N commune lipid extract represses the expression of proinflammatory genes in RAW 264.7 macrophages, at least in part, by inhibiting the activation of NF-kappaB pathway.