The lipopolysaccharide structures of Salmonella enterica serovar Typhimurium and Neisseria gonorrhoeae determine the attachment of human mannose-binding lectin to intact organisms

Mannose-binding lectin (MBL) is an important component of the innate Immune system. It binds to the arrays of sugars commonly presented by microorgani sms and activates the complement system independently of antibody. Despite detailed knowledge of the stereochemical basis of MBL binding, relatively l ittle is known about how bacterial surface structures influence binding of the lectin. Using flow cytometry, we have measured the binding of MBL to a range of mutants of Salmonella enterica serovar Typhimurium and Neisseria g onorrhocae which differ in the structure of expressed lipopolysaccharide (L PS), For both organisms, the possession of core LPS structures led to avid binding of MEL, which was abrogated by the addition of O antigen (Salmonell a serovar Typhimurium) or sialic acid (N, gonorrhoeae). Truncation of the L PS within the core led to lower levels of MBL binding, It was not possible to predict the magnitude of MBL binding from the identity of the LPS termin al sugar alone, indicating that the three-dimensional disposition of LPS mo lecules is probably also of importance in determining MBL attachment. These results further support the hypothesis that LPS structure is a major deter minant of MBL binding.