Expression of Various Pattern Recognition Receptors in Gingival Epithelial Cells

Innate immune response is initiated by the recognition of unique microbial molecular patterns through pattern recognition receptors (PRRs). The purpose of this study is to dissect the expression of various PRRs in gingival epithelial cells of differentiated versus undifferentiated states. Differentiation of immortalized human gingival epithelial HOK-16B cells was induced by culture in the presence of high $Ca^{2+}$ at increased cell density. The expression levels of various PRRs in HOK-16B cells were examined by realtime reverse transcription polymerase chain reaction (RTPCR) and flow cytometry. In addition, the expression of human beta defensins (HBDs) was examined by real time RT-PCR and the amounts of secreted cytokines were measured by enzyme linked immunosorbent assay. In undifferentiated HOK-16B cells, NACHT-LRR-PYDcontaining protein (NALP) 2 was expressed most abundantly, and toll like receptor (TLR) 2, TLR4, nucleotide-binding oligomerization domain (NOD) 1, and NOD2 were expressed in substantial levels. However, TLR3, TLR7, TLR8, TLR9, ICE protease-activating factor (IPAF), and NALP6 were hardly expressed. In differentiated cells, the levels of NOD2, NALP2, and TLR4 were different from those in undifferentiated cells at RNA but not at protein levels. Interestingly, differentiated cells expressed the increased levels of HBD-1 and -3 but secreted reduced amount of IL-8. In conclusion, the repertoire of PRRs expressed by gingival epithelial cells is limited, and undifferentiated and differentiated cells express similar levels of PRRs.