Figure 1.

Summary: Proteoglycan (PG) interactions with the innate immune system. At the cell membrane, PGs can engage Toll-like receptor (TLR) homo- or heterodimer complexes, or heteromeric complexes of TLRs with other receptors such as CD44. Glycosaminoglycan (GAG) chains can also activate TLRs, as can hyaluronan, which is often bound to PGs. Intracellularly, at least one PG (biglycan) can activate the NLRP3 inflammasome. MMP, matrix metalloprotease; TRIF, TIR-domain-containing adaptor-inducing interferon β.