Toll-like receptor 2 is at least partly involved in the antitumor activity of glycoprotein from Chlorella vulgaris.

Toll-like receptors (TLR) are involved in innate immunity by recognizing various bacterial components. We have previously reported that an active substance of ARS-2 purified from the culture medium of Chlorella vulgaris was a glycoprotein with a molecular weight of 63,100 amu and that this glycoprotein expressed antitumor activity, with the protein moiety in ARS-2 being necessary for this antitumor activity. Here, we show that ARS-2 stimulated spleen-adherent cells from C3H/HeJ lacking functional TLR4 to produce interleukin-12 (IL-12) p40, whereas such cytokine production was significantly impaired in ARS-2-stimulated spleen-adherent cells from TLR2 knockout mice. The overexpression of mouse TLR2 (mTLR2) and mouse CD14 (mCD14) conferred the ARS-2 inducibility of nuclear factor-kappaB activation to human HEK 293 cells. These results suggest that TLR2 signaling is at least partly involved in the antitumor activity of the water-soluble antitumor glycoprotein from C. vulgaris.