Research Institute for Plague Control, Rostov-on-Don, Russia
Investigation of ability of Francisella tularensis S- and R-lypopolysaccharide (LPS) preparations as well as the live bacteria with different chemotypes to interact with human lypopolysaccharide-binding protein (LBP) was carried out. It was found that LPS preparations derived from virulent (S-LPS) or isogenic avirulent mutant (R-LPS) strains of F.tularensis had markedly lower affinity to LBP as compared with typical S-LPS of Salmonella abortus and R-LPS of Yersinia pestis. It was shown that R-LPS preparation from avirulent mutant binds LPB more effectively than S-LPS from F.tularensis virulent strain. Differences in S- and R-LPS affinity were also confirmed for LPS represented by the live cells. Thus, bacteria with S-chemotype of LPS (F.tularensis 15/10) bound only 20.3% of LBP, whereas cells with R-LPS (F.tularensis 543 cap-/sup>) bound 39.9%. Such pattern was observed in experiments with both normal non-immune human serum and sera from people immunized with live tularemia vaccine. The latter indicates that opsonization of LPS by specific antibodies does not change its affinity to LBP. The observed more efficient binding of avirulent strain R-LPS to LBP is likely determines the more intensive host response directed to destruction and rapid elimination of the causative agent. At the same time, weak affinity of the vaccine and virulent strains S-LPS to LBP probably allows the bacterium to avoid activation of host defense mechanisms thus contributing to its long-term persistence in microorganism and development of specific immunity against tularemia.
Zh. Mikrobiol. (Moscow), 2008, No. 4, P. 16—21