In response to tissue injury, hyaluronan (HA) polymers are cleaved by host hyaluronidases, generating small fragments that ligate Toll-like receptors (TLRs) to elicit inflammatory responses.
Pathogenic bacteria such as group B Streptococcus (GBS) express and secrete hyaluronidases as a mechanism for tissue invasion, but it is not known how this activity relates to immune detection of HA.
Researchers found that bacterial hyaluronidases secreted by GBS and other Gram-positive pathogens degrade pro-inflammatory HA fragments to their component disaccharides.
In addition, HA disaccharides block TLR2/4 signaling elicited by both host-derived HA fragments and other TLR2/4 ligands, including lipopolysaccharide.
Application of GBS hyaluronidase or HA disaccharides reduced pulmonary pathology and pro-inflammatory cytokine levels in an acute lung injury model.
Authors conclude that breakdown of host-generated pro-inflammatory HA fragments to disaccharides allows bacterial pathogens to evade immune detection and could be exploited as a strategy to treat inflammatory diseases.