Reply to Moran: Modification of Campylobacter jejuni Lipid A

This is a response to a letter by Anthony P. Moran (1)

We have identified the machinery that replaces an ester- by an amide-linked acyl chain in the lipid A of Campylobacter jejuni and demonstrated that changing the distribution of acyl chain linkages alters the response of the TLR4-MD2 complex as well as the susceptibility to antimicrobial peptides (2). This novel lipid A modification mechanism adds to the large repertoire of lipopolysaccharide (LPS) modification strategies to alter the innate immune response (3). As pointed out by Moran and discussed in our manuscript, C. jejuni has evolved multiple other ways to modify its lipid A and thus the host response (4, 5). Our mass spectrometry, comparing equal amounts of LPS, indicates only minor differences in the distribution of lipid A isoforms between the analyzed strains and no evident changes in the number of phosphate molecules or polar head groups. Similarly, the amount of phosphoethanolamine attached to the lipid A, which influences the resistance to polymyxin B (5), seems unchanged, although this may require more thorough chemical analysis. Although how the altered acyl chain linkages exactly influence the structure-bioactivity relationship remains to be resolved, the large biodiversity of the C. jejuni lipid A indicates that this trait is an important asset of this principal bacterial foodborne pathogen that may contribute to bacterial pathogenesis and/or bacterial survival in different environmental niches.