Unusual Interaction of a Lipopolysaccharide Isolated fromBurkholderia cepaciawith Polymyxin B

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Abstract
We have demonstrated that lipopolysaccharide (LPS) obtained fromBurkholderia cepacia, an important opportunistic pathogen, has unique characteristics in both structure and activity. One of the structural characteristics is that theB. cepaciaLPS has 4-amino-4-deoxy-l-arabinose (Ara4N) in its inner core region. Polymyxin B (PmxB) is known to act as an LPS antagonist, but LPS with Ara4N is suggested to be PmxB resistant by decreasing the binding capability of PmxB. Interaction ofB. cepaciaLPS with PmxB was investigated and compared with that of a reference LPS ofSalmonella entericaserovar Abortusequi, referred to hereafter as the reference LPS.B. cepaciaLPS suffered no suppressive effect of PmxB in its activity to stimulate murine peritoneal macrophages for induction of tumor necrosis factor alpha (TNF-α) and IL-6 even when the activity of the reference LPS was completely suppressed. A characteristic ofB. cepaciaLPS is that it has selectively weak interleukin-1β (IL-1β)-inducing activity while activity to induce TNF-α and IL-6 has been shown to be as strong as that of the reference LPS. Remarkably, PmxB augmented the IL-1β-inducing activity ofB. cepaciaLPS to the level of that of the reference LPS and, in contrast, completely suppressed the strong activity of the reference LPS. Using PmxB-immobilized beads, the adsorbances of these LPSs to the beads were compared, and it was found thatB. cepaciaLPS bound to PmxB with a high affinity similar to that of the reference LPS. These results indicate an unusual interaction ofB. cepaciaLPS with PmxB wherebyB. cepaciaLPS not only allows the binding of PmxB with high affinity, even though it contains Ara4N, but also suffers no suppressive effect of PmxB on its activity. Moreover, a remarkable increase in its IL-1β-inducing activity was also observed.