Fig 6.

ΔlptA mutants of N. meningitidis strain 7946 bacteria and LOS induce less TNF-α in THP-1 cells than the wild-type 7946 strain or N. meningitidis strain 89I bacteria or LOS. In the high-resolution negative-ion MALDI-TOF mass spectrum of intact LOS from the mutant, the labeled masses represent the monoisotopic ions, and the numbers presented in red label peaks for prompt fragment ions for LA. Peaks at m/z 1,792.08 and m/z 1,712.12 are consistent with the expression of TPLA and DPLA. As anticipated, there was no evidence of PEA substitution on the LA. The graphs of TNF-α induction by 89I, wild-type 7946, and 7946 ΔlptA mutant bacteria and LOS show that the absence of LA PEA significantly reduces the induction of TNF-α (*, P < 0.01, and **, P < 0.001, compared with the results for 7946 and 89I). The results presented are the means ± standard deviations from at least three independent experiments.