The Role of the Physical State of Lipopolysaccharides in the Interaction with Complement

Abstract

Lipopolysaccharides [e.g., Salmonella bareilly, S. typhimurium] interact with [guinea pig] complement only when the are present in a state of high aggregation with a high apparent MW. Lipopolysaccharides in uniform salt forms, prepared by electrodialysis and neutralization with different bases, exhibited distinct differences in their anticomplementary activity which correlated with differences in their sedimentation coefficients. Conversion of smooth (S) form lipoplysaccharides into the low MW triethylamine form completely abolished their anti-complementary activity; conversion into the high MW Na form increased their activity. A similar treatment of highly defective Re and Rd rough (R) form lipopolysaccharides had no effect no their ability to interact with complement. The triethylamine and Na forms were strongly anti-complementary despite large differences in their MW. This was due to property of R lipopolysaccharides to reaggregate into a large MW form through absorption of Mg2+ and Ca2+ present in the guinea pig serum used as complement source. Defective lipopolysaccharides derived from the Ra and Rb classes showed only negligible anti-complementary activity which did not increase by conversion into salt forms with high MW.