Free lipid A of BordeteUa pertussis, Neisseria meningitidis, and Escherichia coli lipopolysaccharide (LPS) was prepared by hydrolysis in acetate buffer (pH 4.5); in addition, lipid A from B. pertussis and E. coli was prepared by hydrolysis in mineral acid (HCI). The precipitates obtained were purified by extraction methods in toluene-methanol and are referred to as crude lipid A. Purified lipid A from N. meningitidis and B. pertussis was obtained by extraction in a mixture of

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... -water-triethylamine. The different preparations were tested for their pyrogenicity (endogenous pyrogen; EP) and their capacity to trigger the release of interleukin-l (IL-1; previously known as lymphocyte-activating factor; LAF) by human monocytes. Crude lipid A from E. coli and N. meningitidis were both IL-1 inducers. Crude B. pertussis lipid A (acetate buffer; pH 4.5), which contains a 3-1-6-linked D-glucosamine disaccharide, two phosphoryl groups, and five fatty acids, was pyrogenic and an IL-1 inducer (EP+/LAF+); but crude B. pertussis lipid A (0.25 N HCI), which lacked the glycosidic phosphoryl group, was 1,000-fold less pyrogenic than the diphosphorylated lipid A, yet it retained its IL-l-inducing capacity (EP-/LAFt). Purified N. meningitidis lipid A was not an inducer of IL-1 release and purified B. pertussis lipid A exhibited identical pyrogenicity as the parent LPS but was devoid of any IL-l-release inducing capacity (EP /LAF-). These results demonstrate that for some endotoxins, purified lipid A is unable to induce IL-1 release by human monocytes; however, it is pyrogenic, supporting the hypothesis that IL-1 and EP are induced by different determinants on the LPS molecule.