Induction of nitric oxide production in RAW264.7 cells under serum-free conditions by O-antigen polysaccharide of lipopolysaccharide.

BACKGROUND Lipopolysaccharide derived from Pantoea agglomerans (LPSp) mainly consists of two aggregates, the high-molecular aggregate (HMM-LPSp) and the low-molecular aggregate (LMM-LPSp). The structural differences between HMM-LPSp and LMM-LPSp seem to depend on the length of the O-antigen polysaccharide because the lipid A regions of the two fractions are quite similar. In this study, we examined the biological activity of LPSp focusing on the O-antigen polysaccharide using HMM-LPSp and LMM-LPSp under serum-free conditions. MATERIALS AND METHODS The binding of LPSp to RAW264.7 cells under serum-free conditions was analyzed by flow cytometry using LPSp-conjugated fluorescein isothiocyanate (FITC-LPSp). The biological activities of HMM-LPSp and LMM-LPSp under serum-free conditions were evaluated by the nitric oxide production. RESULTS FITC-LPSp showed higher fluorescence intensity under serum-free than serum-containing conditions. HMM-LPSp induced higher nitric oxide production than LMM-LPSp under serum-free conditions. CONCLUSION The present study indicates that the reactivity of LPSp is affected by the O-antigen polysaccharide under serum-free conditions.