Structural variation of Lipopolysaccharide (LPS) contributes to differential activation of the complement pathway 2664

Abstract Description Bacterial pathogens have evolved many ways to evade complex processes of the innate immune system that are integral to the overall health of an individual. In Gram negative pathogens a commonly used immune evasion system is to alter an outer membrane molecule called lipopolysaccharide (LPS). There are three components of LPS, the membrane anchor lipid A, core oligosaccharide, and repeating units of O-antigen. These studies focus on how variation in O-antigen structure affect the level of innate immune activation using murine model systems. O-antigen occupies the extracellular space and interacts with proteins found in the blood. In this space, LPS activates the complement signaling cascade leading to formation of a membrane attack complex (MAC) pore in the bacterial membrane causing cell death. Using ex vivo murine serum, Western blot analysis of cleaved complement cascade protein C3 shows that LPS with shortened or missing O-antigen initiate a significantly lower amount of complement activation. To further examine how the length of the O-antigen chain plays a role in bacterial susceptibility to attack by the MAC, strains of Escherichia coli with different O-antigen lengths were incubated with mouse serum and bacteria survival are quantified by colony enumeration. Understanding how LPS structure contributes to evasion of the complement pathway will potentially lead to novel therapeutic targets that can be used to treat bacterial sepsis. Funding Sources NIH/NIGMS T32GM146694 Topic Categories Innate Immune Responses and Host Defense: Molecular Mechanisms (INM)