A comparison of the immunological potency of Burkholderia lipopolysaccharides in endotoxemic BALB/c mice

Lipopolysaccharide is one of the virulence factors of the soil‐borne pathogens Burkholderia pseudomallei, B. thailandensis, B. cenocepacia and B. multivorans, which cause septic melioidosis (often in B. pseudomallei infections but rarely in B. thailandensis infections) or cepacia syndromes (commonly in B. cenocepacia infections but rarely in B. multivorans infections). The inflammatory responses in Burkholderia LPS‐induced endotoxemia were evaluated in this study. Prior to induction, the conserved structures and functions of each purified LPS were determined using electrophoretic phenotypes, the ratios of 3‐hydroxytetradecanoic to 3‐hydroxyhexadecanoic acid and endotoxin units. In an in vitro assay, cytokine expression of myeloid differentiation primary response gene 88 and Toll/IL‐1 receptor domain containing adapter‐inducing INF‐β‐dependent signaling‐dependent signaling differed when stimulated by different LPS. Endotoxemia was induced in mice by s.c. injection as evidenced by increasing serum concentrations of 3‐hydroxytetradecanoic acid and the septic prognostic markers CD62E and ICAM‐1. During endotoxemia, splenic CD11b⁺I‐A⁺, CD11b⁺CD80⁺, CD11b⁺CD86⁺ and CD11b⁺CD11c⁺ subpopulations increased. After induction with B. pseudomallei LPS, there were significant increases in splenic CD49b NK cells and CD14 macrophages. The inflamed CD11b⁺CCR2⁺, CD11b⁺CD31⁺, CD11b⁺CD14⁺, resident CD11b⁺CX₃CR1⁺ and progenitor CD11b⁺CD34⁺ cells showed delayed increases in bone marrow. B. multivorans LPS was the most potent inducer of serum cytokines and chemokines, whereas B. cenocepacia LPS induced relatively low concentrations of the chemokines MIP‐1α and MIP‐1β. Endotoxin activities did not correlate with the virulence of Burkholderia strains. Thus factors other than LPS and/or other mechanisms of low activity LPS must mediate the pathogenicity of highly virulent Burkholderia strains.