Lipopolysaccharide from Yoshino cedar trees (Cryptomeria japonica) induces high levels of human macrophage polarization

Japanese cedar, Cryptomeria japonica, is an evergreen conifer native to Japan and is often used as a building material. The humidity control properties of wood are known, but there have been few detailed analyses of its effects on living organisms. Therefore, we investigated the effects of cedar water-soluble components on human macrophages, which are essential for maintaining biological homeostasis and innate immunity. In this study, we prepared aqueous extracts from Cryptomeria japonica in Yoshino, Nara prefecture (called as Yoshino cedar). Yoshino cedar aqueous extracts stimulated macrophages toward the classically activated phenotype and inhibited the macrophage phenotype thought to mediate allergic responses. Next, we measured the lipopolysaccharide (LPS) concentration in the Yoshino cedar aqueous extract and found it was present at a high concentration. The major receptor of LPS is Toll-like receptor 4 (TLR4). To confirm whether LPS in Yoshino cedar aqueous extracts activate macrophages through the LPS/TLR4 pathway, we analyzed its effects on TLR4-deficient mouse embryonic fibroblasts (MEF) and wild-type (WT) MEF. TLR4-deficient MEF did not produce the proinflammatory cytokines seen in WT MEF. This result showed that LPS in the Yoshino cedar aqueous extracts activate macrophages via TLR4. This information will help us better understand the benefits of cedar for human health, including allergies.