Genetic Polymorphism of Beta-Defensin 2 and Association with Tongue Coating

The beta-defensins (hBDs), antimicrobial peptides, are expressed by epithelial cells, including the oral epithelium, and may have a protective role in the oral mucosa. Genetic variations of hBDs may be associated with susceptibility to infection and mucosal diseases. Objective: The present study investigated the single-nucleotide polymorphisms (SNPs) in the hBD-2 gene in a group of Japanese individuals and evaluated if the hBD-2 SNPs are associated with tongue coating with bacteria. Methods: Forty unrelated Japanese individuals over 70 years old were sampled. The DNA was extracted from swab samples of the buccal mucosa. The tongue coating was assessed from its thickness and area on the dorsal surface of the tongue, as previously reported by Kojima (grade　0-4). The promoter and coding sites in hBD-2 genes were amplified by PCR. Sequencing was performed with the ABI PRISM 310 Genetic analyzer. The SNPs were also confirmed by the modified Invader method with LightCycler ^TM (Roche Diagnostics, Germany). Haplotype analysis was performed with the Arlequin, a population genetics software. Fisher’ exact probability test with P values of < 0.05 was used for determination of statistical significance of the data. Results: Fifteen subjects had no obvious tongue coating (grade 0 -1), and 25 subjects had severe tongue coating (grade 2-4). We identified 12 SNPs in the promoter up to position –1500 and 2 in coding regions of hBD-2. The most common and rare SNPs were at positions -108 (T-C, allele frequency 0.4531) and + 1980 (C-G, allele frequency 0.0156), respectively. Twenty three haplotypes were defined. According to the statistical tests, there was no difference in the probability between no and severe tongue coating at any SNP. Conclusion: The present study shows the genotype variability of hBD-2 in Japanese individuals, and may provide useful information for genetic research on susceptibility to bacterial infection.