Kinetic studies of the production of nitric oxide (NO) and tumour necrosisfactor-alpha (TNF-alpha) in macrophages stimulated with Burkholderia pseudomallei endotoxin

The mechanism by which Burkholderia pseudomallei survives in macrophages is not clearly understood. In this study, we demonstrated that the mouse macr ophage cell line (RAW 264.7) treated with lipopolysaccharide (LPS) from B. pseudomallei (BP-LPS) produced significantly less NO and TNF-alpha compared with those stimulated with the LPS from Escherichia coli and Salmonella ty phi. The time required for the BP-LPS to trigger substantial NO and TNF-alp ha release was at least 30 min, compared with < 5 min for the E. coli-LPS. A time course study of inducible nitric oxide synthase (iNOS) protein expre ssion also indicated that the time required for macrophages stimulated with the BP-LPS to up-regulate iNOS was longer. The longer time lag for the BP- LPS to activate macrophages was probably due to the delay in up-regulation of iNOS and TNF-alpha mRNA transcription. These results indirectly suggest that the delay of the mediators' production may be due to a reduced rate of signal transduction initiated by the interaction of BP-LPS with the macrop hage cell surface. The use of MoAb to phosphorylated p38 in a Western blot analysis provided data compatible with the notion that the maximum level of phosphorylated p38 from the cells activated with BP-LPS was attained at a slower rate. These results suggest that the unique structure of BP-LPS exhi bits a property which may interfere with macrophage cell activation.