Neisseria meningitidis capsular polysaccharides induce inflammatory responses via TLR2 and TLR4-MD-2

CPS are major virulence factors in infections caused by Neisseria meningitidis and form the basis for meningo-coccal serogroup designation and protective meningo-coccal vaccines. CPS polymers are anchored in the meningococcal outer membrane through a 1,2-diacyl-glycerol moiety, but the innate immunostimulatory ac-tivity of CPS is largely unexplored. Well-established hu-man and murine macrophage cell lines and HEK/TLR stably transfected cells were stimulated with CPS, puri-fied from an endotoxin-deficient meningococcal sero-group B NMB-lpxA mutant. CPS induced inflammatory responses via TLR2- and TLR4-MD-2. Meningococcal CPS induced a dose-dependent release of cytokines (TNF-, IL-6, IL-8, and CXCL10) and NO from human and murine macrophages, respectively. CPS induced IL-8 release from HEK cells stably transfected with TLR2/6, TLR2, TLR2/CD14, and TLR4/MD-2/CD14 but not HEK cells alone. mAb to TLR2 but not an isotype control antibody blocked CPS-induced IL-8 release from HEK-TLR2/6-transfected cells. A significant reduc-tion in TNF- and IL-8 release was seen when THP-1-and HEK-TLR4/MD-2-CD14- but not HEK-TLR2- or HEK-TLR2/6-transfected cells were stimulated with CPS in the presence of Eritoran (E5564), a lipid A antagonist that binds to MD-2, and a similar reduction in NO and TNF- release was also seen in RAW 264.7 cells in the presence of Eritoran. CD14 and LBP enhanced CPS bio-activity, and NF-B was, as anticipated, the major sig-naling pathway. Thus, these data suggest that innate immune recognition of meningococcal CPS by macro-phages can occur via TLR2- and TLR4-MD-2 pathways. J. Leukoc. Biol. 89: 469–480; 2011