Biological activities of Brucella abortus lipopolysaccharides

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Abstract
Purified lipopolysaccharide (LPS) from smooth (S) and rough (R) strains of B. abortus and lipid A isolated from S-LPS by mild acid hydrolysis were examined in several assays of biological activity. Brucella S- and R-LPS and Brucella lipid A activated the complement cascade. Previously reported mitogenic activation by Brucella LPS of spleen cells from endotoxin-resistant C3H/HeJ mice was confirmed and also produced by isolated Brucella lipid A. Mitogenicity was not inhibited by polymyxin B, and amino acid analysis showed no binding of polymyxin B to Brucella LPS under conditions in which mitogenicity of phenol-water-extracted Escherichia coli LPS was inhibited. S and R Brucella LPS and lipid A all produced equivalent polyclonal stimulation of C3H/HeJ and C3H/HeAU spleen cells. Crude and purified LPS from S but not from R B. abortus was toxic for outbred mice, with LD50 approximately 6 times greater than that for E. coli LPS. S- and R-LPS were abortifacient in pregnant outbred mice. S Brucella LPS was lethal for carrageenen-pretreated C3H/HeJ and C3H/HeAU mice; only C3H/HeAU mice were killed by E. coli LPS. The unique fatty acid composition of Brucella lipid A is seemingly responsible for its biological activity in endotoxin-resistant C3H/HeJ mice. The participation of the protein strongly bound to the lipid A cannot be excluded, but its mode of action, if any, is different from that of the lipid A-associated protein of enterobacterial LPS.