Porphyromonas gingivalis lipopolysaccharide stimulation of human monocytes: dependence on serum and CD14 receptor

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Abstract
The purpose of this study was to investigate factors influencing the ability of lipopolysaccharide (LPS) derived from Porphyromonas gingivalis to elicit secretion of tumor necrosis factor-alpha (TNF alpha) from human monocytes (adherent mononuclear cells). The results indicate that P. gingivalis LPS stimulation of TNF alpha from monocytes is comparable to LPS from Escherichia coli. Both LPS, although structurally different, increased TNF alpha secretion in a dose-dependent manner. In serum-free conditions, TNF alpha secretion was relatively low, but it dramatically increased at human serum concentrations as low as 1%. Maximal secretion was observed in the presence of 10% serum, with a slight decrease at higher serum concentrations. The CD14 molecule is a putative monocyte LPS receptor. When cells were pre-incubated with a blocking monoclonal antibody (My4) to CD14, TNF alpha-mRNA accumulation and TNF alpha secretion were reduced to control levels at LPS concentrations of up to 10 ng/ml. At higher LPS concentrations, the blocking effect was only partial, in spite of 50-fold excess antibody concentration. The blocking effect was observed only in the presence of serum. The effect of the CD14 antibody was dose-dependent with saturation at 2.5 micrograms/ml. The results suggest that CD14 is one of the major receptors for P. gingivalis LPS but highlight the necessity to investigate other cell-surface receptors mediating P. gingivalis-LPS interactions. These interactions are believed to be important in the pathogenesis of periodontal destruction.