[Effect of lipopolysaccharides on human dendritic cell cultures and its inhibition by polymyxin B]

Dendritic cells have been described as effective antigen presenting cells. Human dentritic cells are highly susceptible to lipopolysaccharide (LPS) tolerance, consisting of a differential deactivation state in which some cellular functions are impaired. LPS tolerance can be experimentally induced in vitro, in which the presence of LPS strongly affects the behavior of cultured dendritic cells. Recombinant proteins obtained from bacterial systems or protein extracts of ectoparasites containing LPS can be used as stimuli to enhance maturation processes in these cells. The present study evaluated the effect of LPS in human dendritic cell cultures, and the activity of polymyxin B as an inhibitor of the LPS effect. Dendritic cells were obtained from peripheral blood monocytes in the presence of IL-4 and GM-CSF, followed by exposure with LPS and PGE2/TNFalpha. Surface markers and cytokine levels were evaluated by flow cytometry. The dendritic cells pre-exposed to single doses of endotoxin demonstrated a reduced capacity to mature, reduced CD83 expression, inhibited secretion of IL-12, TNFalpha, IL-10 and diminished secretion of IL-6. Furthermore, polymyxin B at 10 mg/ml inhibits LPS activity at 1 mg/ml. The maximum polymyxin B concentration with no effect on cellular morphology was 50 mg/ml. Consequently, polymyxin B was determined to be an effective LPS inhibitor in dendritic cell cultures.