Antibodies against the "core" glycolipid of Enterobacteriaceae (2-keto, 3-deoxyoctonate-Lipid A) have been associated with protection against the sequelae of gram-negative rod bacteremia. To investigate the nature of this protection, dogs and rabbits were immunized with purified glycolipid prepared by phenol-chloroform-petroleum ether extraction of the "Re" mutant of Salmonella minnesota 595 and opsonophagocytic and bactericidal tests were carried out using lapine peritoneal granulocytes and serum factors. Whereas 1-4 mug/kg of glycolipid i.v. produced hypotension in dogs and 8 mug/kg i.v. was lethal, a rising dosage schedule of immunization with an average total dose of 1 mg/kg produced striking protection against shock and death against challenge with heterologous organisms. 20 control dogs, given approximately 10(10) live, serum-resistant Escherichia coli 0.85:H9 or Serratia marcescens 03 during a continuous intra-arterial pressure transducer recording, showed a drop in mean systolic pressure from 186 (+/- 6 SE) to 101 (+/- 12 SE) MM Hg and a fall in mean diastolic pressure from 118 (+/- 3 SE) to 64 (+/- 8 SE) mm Hg within 60-120 min. Minor pressure changes (average less than 12% of prechallenge levels) were seen in the same number of immunized dogs. In contrast, no significant difference was noted in the bloodstream clearance of these serum-resistant organisms over a period of 4-6 h between immunized and control dogs. Intravascular clearance was greater in animals immunized with the challenged strain or in glycolipid-immunized animals challenged with highly serum-sensitive E. coli 0.14:K7. Antibody against core glycolipid protected against the hemodynamic sequelae of bacillemia, augmented intravascular clearance of serum-sensitive organisms, and abrogated the pyrogenic response to enteric bacilli, but did not enhance clearance of serum-resistant organisms. Although canine and lapine antiserum against core glycolipid passively protected mice against a heterologous challenge, opsonophagocytic and bactericidal activity was at least 100-fold less than type-specific antiserum.
L S Young, P Stevens, J Ingram
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