Galectin－9 is one of the galectin molecules which binds to β－galactoside and has immunoregulatory functions such as T cell apoptosis and regulatory T cell induction. In our previous studies using human monocyte-like cell line U937 cells, we reported that fucoidan, but not lychee extract and catechin, effectively shows signs of immunostimulatory functions by enhancing production of proinflammatory cytokines such as TNF－ α , IL－1 β , and IL－6, while also suppressing the production of inhibitory cytokines such as IL－10 and TGF－β, and it was suggested there is a possibility that the decreased expression of galectin－9 might be involved in this process. In this study, we investigated expression of galectin－9 and proinflammatory cytokine production in the presence of fucoidan by using human peripheral blood mononuclear cells （PBMC） which include multiple immunocytes such as monocytes, T cells, and/or NK cells. As a result, it was shown that fucoidan down-regulates expression of galectin－9 and demonstrates immunostimulatory functions effectively by enhancing production of proinflammatory cytokines while suppressing the production of inhibitory cytokines in PBMC stimulated by LPS just like it does with U937 cells. It was also suggested that fucoidan has immunostimulatory functions on Th2 cells and Th17 cells due to enhanced production of IL－4 and IL－17 in PBMC stimulated by T cell-mitogen such as concanavalin A（ ConA）
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