Recognition Receptors for β-Glucans

Dectin-1 is often referred to as the β-glucan receptor. Dectin-1 is expressed on monocytes, macrophages, neutrophils, dendritic cells, and T lymphocytes, activated by the binding of β-glucans . The receptor is also present in mucosal immune cells where pathogens invade. By regulating the inflammasome and transcription factor activation, this binding generates cytokines, chemokines, and reactive oxygen species (ROS) . This recognition relies on the 1,3 backbone . Several other receptors react to β-glucans, including lactosylceramide, scavenger, and Toll-like receptors. Toll-like receptor (TLR2) binding causes ROS, pro-inflammatory indicators, and pathogen clearance phagocytosis . The pathway activated after binding can either stimulate the immune response and initiate a cascade of inflammatory mediators or, in contrast, dampen down inflammation through modulatory processes .

When β-glucans bind to Dectin-1, it increases phosphorylation of its intracellular immunoreceptor tyrosine-based activation motif (ITAM) and Syk and activates the PI3K/Akt pathway. This finally results in phagocytosis, the creation of ROS, microbial death, and cytokine release . A more detailed graphical representation of this process can be found at .

Neutrophils, monocytes, and natural killer (NK) cells express the CR3 receptor. CR3 is distinctive in that it contains two different binding sites for ligands. A carbohydrate-binding lectin-like domain, which can bind β-glucans, serves as the second ligand-binding site. Binding will enhance cytotoxicity against iC3b-opsonized target cells such as tumour cells, phagocytosis, and degranulation . The CR3 produced by innate cells such as macrophages, dendritic cells, natural killer cells, and neutrophils binds to yeast-derived low molecular weight soluble β-glucans. The CR3 receptor is activated by the binding of soluble β-glucans and iC3b, and this leads to the destruction of tumour cells coated with iC3b through CR3-dependent cellular cytotoxicity (DCC) .