M043: THE INDUCTION OF TNF BY B. CEPACIA AND P. AERUGINOSA
LIPOPOLYSACCHARIDE
D. Shaw, I.R. Poxton and J.R.W. Govan (Department of
Medical Microbiology, University Medical School, Edinburgh, Scotland).
In contrast to the increasing knowledge of Burkholderia cepacia epidemiology, information on the pathogenic potential of this organism remains scarce. Preliminary in-vivo data has shown that CF patients colonised with B. cepacia (Bc) exhibit higher levels of inflammatory markers than P. aeruginosa (Pa) colonised-patients. In this study, we investigated TNF induction by Bc and Pa lipopolysaccharide (LPS). TNF is a major cytokine responsible for the secretion of several immune-mediated markers. It can be induced from immune cells by a variety of agents including bacterial LPS. LPS binding to immune cells can be facilitated by a complex of LPS-binding protein and CD14 cell surface receptors. We have shown previously that in vitro the capacity of Bc LPS to induce TNF from human mononuclear cells, neutrophils and lung epithelial cells is significantly higher than for Pa LPS (p < 0.01). We have now expanded these studies to determine if the enhanced biological activity of Bc compared to Pa is due to different LPS binding pathways and to examine the TNF response when both Bc and Pa LPS were present together as is often the situation in the CF lung. Bc and Pa LPS were used to induce TNF from the monocytic cell line ThP-1 which can be enhanced for the expression of CD14 by the addition of vitamin D3. Our data showed no significant difference between TNF levels from ThP-1 cells with and without enhancement for CD14. When Bc and Pa LPS were added together the levels of TNF induced decreased compared to the levels for Bc alone. This effect was dependent on the amount of Bc LPS present. However, even when Pa LPS was present in a 20-fold excess to Bc LPS the TNF induced was still greater compared to Pa LPS alone. We conclude that both Bc and Pa LPS induce TNF by a pathway independent of CD14 and that the presence of Bc LPS enhances TNF levels even when Pa LPS is present in excess. These results confirm our previous speculation that the inflammatory potential of B. cepacia including stimulation of TNF by LPS, may contribute to destructive pulmonary inflammation.