Fig. 1.

Innate immunity and adaptive immunity. Innate immunity (green): Pathogen-associated molecular patterns (PAMPs), lipopolysacharides (LPS) and bacteria act as stimuli to Toll like receptors (eg. TLR9, TLR2) resulting in increased reactive oxygen species (ROS), inflammation, and decreased sinonasal epithelial barrier function. Damage associated molecular patterns (DAMPs) directly stimulate the release of cytokines (IL-25, IL-33, TSLP) leading to Th2 activation. Taste receptor T2R38 has also been shown to be stimulated by LPS and in turn creates a nitrous oxide dependent immune response. Adaptive immunity (red): Activation of the Th2 pathway via IL-4, IL-5 and IL-13 results in increased epithelial barrier permeability in part through down regulation of tight junction proteins. An IgE mediated immune response results in mast cell degranulation.