Effect of Haemophilus influenzae type b lipopolysaccharide on complement activation and polymorphonuclear leukocyte function.

Purified lipopolysaccharide (LPS) from Haemophilus influenzae type b (Hib) was examined for its capacity to interact with human hemolytic complement, generate conversion products of C3, C4, and factor B, stimulate C5a activity, and affect human neutrophil chemiluminescence and phagocytosis. Salmonella typhimurium LPS and Salmonella minnesota Rb LPS (R345 mutant) were examined for comparison. Incubation of Hib LPS with human serum deficient in gamma-globulin or with normal human serum containing 10 mM EGTA and 7 mM MgCl2 resulted in some depletion of hemolytic complement and conversion of C3 to degradation products (determined by inhibition of passive hemolysis and electrophoresis/immunofixation, respectively), indicating that complement activation occurred by the alternative pathway. Complement activation by Hib LPS and S. minnesota Rb LPS was similar, but significantly less effective than by S. typhimurium LPS (p less than 0.01). Solubilized Hib lipid A, but not LPS, induced conversion products of C4 in hypogammaglobulinemic serum, indicating activation of the classical pathway. Similar levels of C5a activity were generated by incubation of Hib LPS and S. typhimurium LPS in hypogammaglobulinemic serum, as determined by neutrophil shape change and neutrophil aggregation. Hib LPS directly stimulated neutrophil chemiluminescence, whereas S. typhimurium LPS had little effect. Phagocytosis of radiolabeled, opsonized Hib by neutrophils was diminished by S. minnesota Rb LPS, Hib LPS, or solubilized Hib lipid A (p less than 0.001), but was slightly increased by S. typhimurium LPS. Neither the oligosaccharide of Hib LPS or Hib capsular polysaccharide was capable of interacting with complement or altering neutrophil chemiluminescence or phagocytosis.(ABSTRACT TRUNCATED AT 250 WORDS)