Alpha-defensin binding to epithelial cells

Defensins form an important group of antimicrobial peptides fighting against periodontal infections. While beta-defensins are produced mainly by epithelial cells, alpha-defensins are derived primarily from neutrophils. Objectives: We analyzed the localization of alpha-defensins in inflamed gingiva and studied if epithelial cells can produce alpha-defensins in vitro. Methods: Inflamed human gingival specimens were studied by immunohistochemistry using alpha-defensin 1-3 antibodies. We also added isolated human neutrophils or neutrophil extracts or F. nucleatum cells (ATCC 19959) to cultured epithelial cells (HaCaT-human skin keratinocyte line) and analyzed production/binding of alpha-defensins in the epithelial cells, using immunocytochemical methods. Results: In human gingival sections alpha-defensins were localized primarily in junctional epithelium but not in the subepithelial tissue rich of inflammatory cells. We therefore hypothesized that alpha-defensins were either produced by junctional epithelial cells or bound to them following release from neutrophils. The cell culture studies showed no clear evidence that HaCaT epithelial cells were synthesizing alpha-defensins upon stimulation by F. nucleatum or neutrophils. However, epithelial cells bound selectively alpha-defensins released from neutrophils. Peripheral epithelial cells with free margins in the cell colonies bound strongly alpha-defensins. The binding was concentration- and time-dependent. The peptides localized as punctate concentrates inside epithelial cells. Conclusions: Binding of neutrophil alpha-defensins to epithelial cells appears to be an important antimicrobial defense system of junctional epithelium. Storage of broad-spectrum antimicrobial peptides inside epithelial cells may form an effective barrier against microbes attempting to invade periodontium.