Direct effects of polymyxin B on human dendritic cells maturation -: The role of IκB-α/NF-κB and ERK1/2 pathways and adhesion

Polymyxin B is a lipopolysaccharide binding antibiotic used to inactivate potential lipopolysaccharide contaminations when evaluating the activity of different agents on innate immune cells. We report that polymyxin B is able to induce directly in monocyte- derived human dendritic cells ( DCs) several functional and molecular modifications characteristic of DCs undergoing a maturation process. DCs incubated with polymyxin B up- regulate the expression of HLA class I and II, the co- stimulatory CD86 molecule, and show an increase in the fraction of adherent cells at short time, which persist at 48 h of incubation. Adhesion to the plate was required for the polymyxin B- induced DCs maturation. A transient activation of I kappa B- alpha/ NF- kappa B and ERK1/ 2 pathways at short time and a further ERK1/ 2 activation at long term were also detected. Neither up- regulation of the maturation marker CD83 nor activation of p38 nor induction of cytokines secretion was observed in DCs treated with polymyxin B. We demonstrated that inhibition of I kappa B- alpha/ NF- kappa B pathway abolishes polymyxin B effects. ERK1/ 2 inhibition instead allowed DCs treated with polymyxin B to progress in their maturation process as revealed by the increased up- regulation of the CD83 co- stimulatory molecules, the activation of p38, and the reduced adhesion to culture plates at 48 h of incubation. Our results indicate that polymyxin B induces a partial maturation of human DCs through increased adhesion to a substrate and activation of the I kappa B- alpha/NF-kappa B pathway. The increased ERK1/ 2 activation observed, even though correlating with the initial phases of the maturation process, actually inhibits the occurrence of full maturation.