IL1R1 and serum lipopolysaccharide activity: As a possible role for endotoxemia-induced IL-1β-producing myeloid cells in the leptomeninges and choroid plexus, they may function as triggers for the activation of leptomeningeal stromal cells, choroid plexus stromal cells, and choroid plexus epithelial cells to produce cytokines via IL-1β–IL-1R signaling, since IL-1R1 was expressed by these cells.