Campylobacter jejuni Lipooligosaccharide Sialylation, Phosphorylation, and Amide/Ester Linkage Modifications Fine-tune Human Toll-like Receptor 4 Activation

Campylobacter jejuni is a leading cause of acute gastroenteritis. C. jejuni lipooligosaccharide (LOS) is a potent activator of Toll-like receptor (TLR)-4-mediated innate immunity. Structural variations of the LOS have been previously reported in the oligosaccharide (OS) moiety, the disaccharide lipid A (LA) backbone, and the phosphorylation of the LA. Here we studied LOS structural variation between C. jejuni strains associated with different ecological sources and analyzed their ability to activate TLR4 function. MALDI-TOF MS was performed to characterize structural variation in both the OS and LA between 15 different C. jejuni isolates. Cytokine induction from THP-1 cells and monocytes was correlated with LOS structural variation in each strain. Additionally, structural variation was correlated with the source of each strain. OS sialylation, increasing abundance of LA D-glucosamine (GlcN) versus 2,3-diamino-2,3-dideoxy-D-glucose (GlcN3N) and phosphorylation status all correlated with TLR4 activation as measured in THP-1 cells and primary monocytes. Importantly, LOS-induced inflammatory responses were similar to those elicited by live bacteria highlighting the prominent contribution of the LOS component in driving host immunity. OS sialylation status but not LA structure showed significant association with strains clustering with livestock sources. Our study highlights how variations in three structural components of C. jejuni LOS alter TLR4 activation and consequent monocyte activation.