Interaction of the First (C1), the Second (C2) and the Fourth (C4) Component of Complement with Different Preparations of Bacterial Lipopolysaccharides and with Lipid A

Lipopolysaccharides of Gram-negative bacteria (LPS) known to activate the complement system via the alternate pathway bypassing C1̄, C4, and C2 had a direct effect on purified C1̄, but no effect on purified C4 and C2. These studies were performed with different preparations of LPS and of Lipid-A isolated from smooth (S-) and rought (R-) forms of Escherichia coli and Salmonella strains. It was shown that the effect of LPS on C1̄ depends upon the concentration and type of LPS applied: 0.77 µg of LPS from E. coli 0 75, 2.5 µg of LPS from S. minnesota R 595, 24 µg of Lipid-A and 55 µg of Lipid-A/BSA were necessary to get 50% inhibition of free C1̄. In contrast, 100 µg of LPS from E. coli 0 111, from S minnesota S-form, or from S. minnesota R 345 showed no significant inhibition. Binding of C1̄ to EA or EAC4 markedly reduced the effect of LPS and of Lipid-A on C1̄. The inhibition of C1̄ was shown to be the result of a direct interaction of LPS and of Lipid-A with the C1 subunit C1q: LPS precipitated C1q. LPS and Lipid-A had no effect on the C1 esterase activity against C2.