In rats, the natural antimicrobial peptide similar to human LL‑37 (called CRAMP) shows up in tooth‑building cells during development and re‑appears when teeth try to repair damage, hinting it might help form new dentin after a cavity.

Cathelicidin-related antimicrobial peptide (CRAMP) is an antimicrobial peptide in mice and rats homologous to LL-37 in humans. In addition to its antibacterial activity, CRAMP has various physiological functions by binding to formyl peptide receptor 2 (FPR2). However, the role of these peptides in teeth is unknown. Therefore, we investigated the role of CRAMP and FPR2 in tooth development, reparative dentin formation, and defense response. First, we examined the localization of CRAMP and FPR2 during tooth development by immunohistochemical analysis. Next, we investigated the localization of CRAMP, FPR2, and CD68-positive macrophages by immunohistochemical analysis during pulp inflammation and reparative dentin formation after cavity preparation. Finally, we analyzed the effect of lipopolysaccharide (LPS) on the expression of CRAMP and FPR2 in dental pulp cells by real-time reverse transcription PCR. At the late bell stage in tooth development, CRAMP was detected in odontoblasts, and FPR2 was observed in the sub-odontoblastic layer. In mature teeth, CRAMP was not detected, but FPR2 continued to be localized in the sub-odontoblastic layer. After cavity preparation, CRAMP-positive cells and macrophages were found in dental pulp tissues below the cavity at an early stage of repair. At subsequent stages of reparative dentin formation, CRAMP was observed in odontoblast-like cells that contacted reparative dentin. FPR2 immunoreactivity was also detected in odontoblast-like cells and neighboring cells. LPS stimulated the expression of CRAMP mRNA in dental pulp cells in vitro. Localization of CRAMP and its receptor FPR2-positive cells were observed during physiological and reparative dentin formation. CRAMP/LL-37 has a possibility that induce reparative dentin formation.