The response of human gingival fibroblasts to toll-like receptor ligands

Abstract

Periodontitis is a bacterial infection characterized by chronic gingival inflammation, which leads to the loss of tooth-supporting tissue. Recent data demonstrated that human gingival fibroblasts (HGFs) expressed Toll-like receptors (TLRs) 2, 4 and 9. Toll-like receptors (TLRs) are important pattern recognition molecules that trigger innate immune responses via the recognition of conserved pathogen-associated molecular patterns (PAMPs). We hypothesize that pathogen recognition by gingival fibroblast TLRs may contribute to the development of innate immune response. In this study, we investigated the role of HGFs in the innate immunity of periodontium. The mRNA expression of TLRs (TLRs1-10) in HGFs from healthy gingiva was assessed using reverse trancriptase-polymerase chain reaction (RT-PCR). In addition, the responses of HGFs to different TLR ligands were determined. HGFs were stimulated with a single TLR ligand 1), TLR2 ligand (Porphyromonas gingivalis LPS); 2). TLR3 lignad (Polyinosine-polycytidylic acid); 3). TLR4 ligand (Escherichia coli LPS); 4). TLR5 ligand (Salmonella thyphimurium flagellin); 5). TLR7 ligand (Loxoribine); 6). TLR8 ligand (ssPolyU), and 7). TLR9 ligand (CpG2006) or the combination of TLR ligands. After 24 hour incubation, culture supernatants were collected and analyzed for IL-8 production using enzyme-linked immunosorbent assay. RT-PCR results revealed that HGFs expressed mRNA of TLRs1, 2,3,4,5,6, and 9 but did not express mRNA of TLRs 7,8 and 10. We found theat HGFs produced IL-8 in response to TLR 2,3,4,5 ligands, but not TLR9 ligand. The data may indicate non-functional TLR9 or inability to bind/up-take CpG2006 by HGFs. When HGFs were stimulated with the combination of TLR ligands, the IL-8 production was minimally enhanced or remained relatively unchanged as compared with those from single ligand-stimulated HGFs. It is interesting to note that CpG2006 greatly inhibited IL-8 production induced by TLR3 ligand, but not by other TLR ligands. Further investigation for underlying mechanism of this inhibitory effect is needed. In conclusions, our results suggest that HGFs play an important role in innate immunity of the periodontium.