Correlation between β-defensin expression and induction profiles in gingival keratinocytes

Human β-defensins are antimicrobial peptides produced by epithelial cells. To date, 28 β-defensins have been described and the expression of a select few has been classified as constitutive or inducible. Most studies have evaluated expression and regulation using a limited number of primary cell cultures or immortalized cell lines. The goal of this study was to quantitatively assess the in vitro expression and inducibility profiles of human β-defensins, HBD-1, HBD-2, and HBD-3 across a number of primary gingival keratinocyte cultures. Cultured cells from 14 human subjects were stimulated with interleukin-1 beta (IL-1β), IL-2, IL-6, IL-8, IL-12, tumor necrosis factor alpha (TNF-α), gamma interferon (IFN-γ) or Escherichia coli lipopolysaccharide (LPS) and analyzed by reverse transcription (RT)-PCR. A subset of cultures were quantitatively assessed by real-time PCR. HBD-1 presented the highest and most heterogeneous expression at the basal level (non-stimulated) as compared to expression of HBD-2 and HBD-3, which was significantly lower and homogeneous. IFN-γ was a primary inducer for HBD-1 and HBD-3, while IL-1β and TNF-α were primary inducers for HBD-2. Sporadic induction was seen for IL-2, IL-6 and LPS. Synergistic expression was seen when various cytokines were combined. Interestingly, the induction potential of each β-defensin was directly correlated to its basal expression. An inhibitor of JAK2 kinase (Janus kinase), down-regulated IFN-γ-induced HBD-1 and HBD-3 expression, suggesting a role for the JAK/signal transducer and activator of transcription (STAT) signaling pathway in their expression. HBD-2 protein expression of supernatants and cell lysates paralleled mRNA expression. The results suggest that β-defensin expression and induction in gingival keratinocytes is similar to that seen in other tissue. However, the novel finding of considerable variation among induction levels and the correlation of the induction with basal expression suggests that these innate response elements may play a key role in susceptibility or resistance to disease in the oral cavity.