Identification of TLR2/4-mediated phagocytosis and immune response activation pathways by vacuoles isolated from Saccharomyces cerevisiae

The vacuoles of the yeast Saccharomyces cerevisiae are closely related to mammalian lysosomes and play a role in macromolecular degradation due to the hydrolytic enzymes present inside. The vacuoles also regulate osmotic pressure and control cellular homeostasis. In previous results, vacuoles were shown to activate the immune response of macrophages by promoting the production of immune-mediated transporters nitric oxide (NO), reactive oxygen species (ROS), and pro-inflammatory cytokines. In this study, the effects of vacuoles on the phagocytosis activity of RAW264.7 cells and their potential as immune enhancers were evaluated, and receptors capable of recognizing vacuoles were examined. An investigation using the phagocytes assay showed that phagocytosis activity increased by the vacuole. Besides, after treatment with TLR2/4 inhibitor, the expression of pro-inflammatory cytokines by vacuoles was significantly reduced and the inducible nitric oxide synthase (iNOS) protein was also significantly reduced. However, treatment with a TLR2 inhibitor did not reduce the production of interleukin-6 (IL)-6, a pro-inflammatory cytokine. As a result of confirming the activation of TLR2/4 using Western blot and immunofluorescence (IF), the TLR2/4 protein expression and fluorescence intensity increased depending on the concentration of vacuoles. Yeast vacuoles significantly upregulate protein expression of p-p65/p-p38 MAPKs. In summary, the vacuoles isolated from S. cerevisiae in macrophages have increased phagocytic ability at a concentration of 20 (µg/ml) and can function as immune-enhancing agent suggesting that TLR2/4 mediated the p38 MAPK/nuclear factor kappa B signaling pathway.