In a mouse infection model, Salmonella enterica serovar Typhimurium can reside and proliferate within phagocytes in deeper tissues (35,47) and it can follow up to induce macrophage death by a possible necrosis (19). This model has been studied as a model of typhoid fever infection in humans caused by S. enterica serovars Typhi and Paratyphi that remains a significant problem in developing countries (46). Three vaccines against typhoid fever are presently in use. Two are injected, and one is orally administered. The two injected vaccines consist of killed whole bacteria and capsular material (Vi antigen) (51). The one live oral vaccine strain, serovar Typhi Ty21a, is an attenuated strain of mutations in galE (a gene in the galactose utilization pathway that affects O-antigen production) (10) and rpoS ( S ) (48, 49). Generally, an oral vaccine is cheaper, easier, and safer to administer than an injected vaccine. In human field trials, the oral vaccination with serovar Typhi Ty21a proved to be safe and effective, but its efficacy varied considerably from trial to trial (9, 51). To develop more promising vaccine strains, researchers have carried out human trials to test various serovar Typhi vaccine candidate strains that harbor precise mutations in specific genes (29 In the mouse model, at least three distinct genetic loci (ity, lps, and xid) affect the ability of the animal to successfully resist systemic infections by serovar Typhimurium. The ity s (designating susceptible response) allele of BALB/c or C57BL/6 mice and the lps d (designating defective response) allele of C3H/HeJ mice are associated with increased susceptibility to infection (30,62) and decreased susceptibility to endotoxin lethality (44), respectively. The ity phenotype is linked to Nramp1 (61), which encodes a macrophage-specific phosphoglycoprotein that is required by the phagosomal membrane during phagocytosis (15,61). The increased susceptibility to infection is associated with a nonconservative amino acid sub-

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Lipopolysaccharide (LPS) of Burkholderia cepacia was purified by the conventional phenol-water extraction method (preparation BcLPS-1), followed by enzymatic treatments with DNase, RNase, trypsin, and proteinase K (preparation BcLPS-2), and finally by deoxycholate-phenol-water extraction (preparation BcLPS-3). Cells of LPS-hyporesponsive C3H/HeJ mice were activated by both the BcLPS-1 and the BcLPS-2 preparations but barely activated by BcLPS-3. When LPS-responsive C3H/HeN mice were used as targets, endotoxic activities such as lethal toxicity to galactosamine-sensitized mice, mitogenicity to spleen cells, and activation of macrophages to induce tumor necrosis factor alpha and interleukin-6 (IL-6) were strongly exhibited even by highly purified BcLPS-3 at levels comparable to those of the highly active enterobacterial LPS of Salmonella enterica serovar Abortus-equi (SaeLPS), used as the control. The ability of BcLPS-3 to activate murine macrophages for induction of IL-1␤ was, however, much weaker than that of SaeLPS. Both accumulation of pro-IL-1␤ protein and expression of IL-1␤ mRNA in macrophages by stimulation with BcLPS-3 were much weaker than by stimulation with SaeLPS. These results indicate that LPS of B. cepacia has the potential to play a role as a pathogenic factor with strong activity comparable to that of usual enterobacterial LPS, but unlike the latter, this LPS has a relative lack of ability in the activation of murine macrophages to induce IL-1␤. The lack of IL-1␤-inducing ability appears to be caused by incomplete signal transduction somewhere in the upstream step(s) of IL-1␤ gene transcription.Burkholderia cepacia is an aerobic glucose-nonfermenting gram-negative bacillus that possesses flagella and formerly belonged to the genus Pseudomonas (37). Bacteria of this species are intrinsically resistant to many antibiotics and active as opportunistic pathogens in hospitalized patients and other compromised hosts (8,26). Especially among patients with cystic fibrosis, infection by this organism makes possible the development of serious pneumonia and sepsis with a high mortality rate, i.e., "cepacia syndrome" (9). Lipase, protease, extracellular toxic complex, and lipopolysaccharide (LPS) released from the bacteria have been suggested as candidates for the virulence factors which cause pathological changes, such as accumulation of polymorphonuclear leukocytes and proteinaceous exudate in bronchial and alveolar lumina, injury and necrosis of bronchial epithelium, and disorganization of alveolar structure. The specific crucial trigger of the pneumonia and sepsis in B. cepacia infection, however, remains to be clarified (16,20,31,34,39).Among these four candidates, we were interested in LPS, a major component of the outer membrane in gram-negative bacteria, since it is assumed to play a central role in the induction of various pathophysiological responses, such as fever, disseminated intravascular coagulation, and shock in hosts suffering from gram-negative bacterial infections (22,27). LPSs of members o...