GINGIVAL EPITHELIAL-CELLS INCREASE INTERLEUKIN-8 SECRETION IN RESPONSE TO ACTINOBACILLUS-ACTINOMYCETEMCOMITANS CHALLENGE

PERIODONTAL DISEASES RESULT FROM THE INTERACTION Of bacterial pathogen s with the host gingival tissues. The role of gingival epithelial cell s in the initiation of host defense mechanisms after encountering oral bacteria has not been investigated. Actinobacillus actinomycetemcomit ans is a key periodontal pathogen that adheres to and invades oral epi thelial cells. Thus, we examined whether gingival epithelial cells inc rease secretion of the potent neutrophil chemoattractant interleukin-8 (IL-8) following A. actinomycetemcomitans challenge. Normal human ora l keratinocytes (NHOK), isolated from gingival tissue, and 3 oral epit helial cell lines (HOK-18A, HOK-16B-BaP-T1, and HEp-2) were co-culture d with A. actinomycetemcomitans for 2 hours to allow bacteria-epitheli al cell interactions. The epithelial cells were then washed, and fresh medium with gentamicin was added to kill extracellular bacteria. Cell cultures were further incubated for 24 hours before the supernatant w as collected for IL-8 detection with ELISA. The results showed that IL -8 secretion increased 2- to 7-fold 24 hours after bacterial challenge . The highest IL-8 secretion was at the multiplicity of infection (MOI ) of 1,000:1 in bacterial dose response studies using HOK-16B-BaP-T1 c ells. Time-course studies revealed that IL-8 secretion rapidly reached a maximum level 6 hours after bacterial challenge and subsequently de creased to basal levels. These data indicate that gingival epithelial cells are capable of upregulating IL-8 expression rapidly in response to A. actinomycetemcomitans challenge and thus may facilitate the recr uitment of neutrophils as a host defense mechanism.