Evading host immune response by bacteria

Evading host immune response by bacteria

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.