Yersinia enterocolitica O:3 Outer Membrane Vesicles as a Platform for Complement Activation.

Lipopolysaccharide (LPS) is the major component of the outer membrane vesicles (OMVs) of Gram-negative bacteria. We hypothesized that OMVs-induced complement activation contributes to the development of systemic inflammatory response syndrome (SIRS). Yersinia enterocolitica O:3 (YeO3) variants synthesizing LPS of various chemotypes (S, Ra, Rd1, Re) were used as model microorganisms. OMVs activated complement more potently than parental bacteria or homologous LPS, independently of chemotype. A high molecular weight polysaccharide fraction, distinct from LPS, was recognized by serum mannose-binding lectin (MBL). In vivo experiments demonstrated that complement depletion weakened the hallmarks of OMVs-induced SIRS in mice. LPS chemotype affected the biodistribution of OMVs and long O-specific polysaccharide protected them from clearance. Chemotype influenced OMVs secretion with their highest release by bacteria with LPS reduced to the inner core and lipid A (Rd1). The shift from environmental to host's temperature stimulated secretion of smaller OMVs, with less-toxic, tetra-acyl lipid A. Our data are consistent with a contribution of OMVs to Yersinia pathogenicity through complement activation. Their potency as complex virulence factor is influenced by size, length of oligo-/polysaccharide chain, and lipid A form. This study comprehensively characterizes OMV-complement interactions in YeO3, extending the knowledge of mechanisms previously established for other Gram-negative bacteria.