Interleukin-6 in neutrophils from peripheral blood and inflammatory periradicular tissues

Periradicular tissue samples were recovered from patients undergoing endodontic surgery. Immunohistochemical procedures were used to identify interleukin-6 (IL-6) present in the neutrophils associated with these lesions. Using specific polyclonal antibody, 15 to 20% of the neutrophils associated with the periradicular tissue lesions were positive for IL-6. IL-6-positive plasma cells and histiocytes were also abundant. Cytokine production by neutrophils from the peripheral blood of nondiseased individuals was also evaluated. The cells were stimulated with lipopolysaccharides and bacterial extracts of Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis. Significant levels of IL-6 were produced by cells stimulated with Escherichia coli lipopolysaccharide B5 (933 pg/ml/10(7) neutrophils) and E. coli lipopolysaccharide B12 (791 pg/ml/10(7) neutrophils) when compared with unstimulated cells (39.31 pg/ml/10(7) cells). There was a dose-dependent increase in IL-6 production when cells were stimulated for 24 h with 6 and 12 micrograms/ml of A. actinomycetemcomitans extract. Less stimulation occurred with P. gingivalis, but it was also dose-dependent. Neutrophils resident in periradicular lesions may, therefore, provide a source of IL-6 in addition to that produced by tissue histiocytes and plasma cells.