INTERLEUKIN-6 PRODUCTION BY HUMAN MONOCYTES TREATED WITH GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR IN THE PRESENCE OF LIPOPOLYSACCHARIDE OF ORAL MICROORGANISMS

This study focused on the effect of granulocyte-macrophage colony-stim ulating factor (GM-CSF) and lipopolysaccharide of the putative periodo ntal pathogens Porphyromonas gingivalis or Fusobacterium nucleatum on IL-6 production by THP-1 cells (a human monocytic cell line). Resting THP-1 cells were alternatively treated with GM-CSF (50 IU/ml) and lipo polysaccharide of P. gingivalis or F. nucleatum, in varying concentrat ions for varying time periods. IL-6 production in supernatant fluids o f treated cells was evaluated by an enzyme-linked immunosorbent assay (ELISA) and a reverse transcription polymerase chain reaction (RT-PCR) was used to evaluate gene expression. Untreated THP-1 cells did not p roduce IL-6 as determined by ELISA. RT-PCR also failed to detect IL-6 mRNA in untreated THP-1 cells, indicating that IL-6 was not constituti vely produced. After stimulation of THP-1 cells with lipopolysaccharid e of F. nucleatum or P. gingivalis, IL-6 was produced, peaking at 4 h (200-300 pg/ml) and thereafter sharply declining by 8 h. When GM-CSF w as added together with lipopolysaccharide of P. gingivalis or F. nucle atum, there was a synergistic quantitative increase in production of I L-6 as measured by ELISA as compared with lipopolysaccharide alone. IL -6 mRNA was detected by RT-PCR, 15 min after stimulation with lipopoly saccharide of either P. gingivalis or F. nucleatum. CM-CSF supplementa tion with lipopolysaccharide of P. gingivalis shortened the transcript ion of IL-6 mRNA to 5 min, a shift which was not observed with lipopol ysaccharide of F. nucleatum, possibly indicating a different mechanism of initiation of transcription. Production of IL-6 by GM-CSF-treated THP-1 cells in the presence of lipopolysaccharide of oral microorganis ms may provide a model for studying the role of macrophages in acute a nd chronic periodontal diseases, including the clinical periodontal ex acerbation as observed in chemotherapy patients receiving GM-CSF for b one marrow recovery.