Saliva Prevents Degradation of LL-37 by Porphiromonas gingivalis

The antibacterial propeptide hCAP18 (human cationic peptide 18 kDa) is expressed by neutrophils and most epithelial cells. hCAP18 is processed to generate the active LL-37 antibacterial peptide which is found in human saliva. Salivary LL-37 deficiency was correlated with susceptibility to periodontal disease in patients with morbus Kostmann disease. Objective: In this study we tested the ability of periopathogenic bacteria to degrade LL-37 in human saliva. Methods: Synthetic LL-37 was incubated with culture supernatants collected from Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans and Streptococcus mutans. Incubations were performed with or without whole or parotid saliva collected from healthy volunteers. After incubation, peptide integrity was detected by Western blot immunodetection using rabbit anti-human LL-37 antibodies. Results: P. gingivalis supernatant degraded LL-37. Whole saliva (native or boiled), as well as parotid saliva (native or boiled), prevented LL-37 degradation. Neither A. actinomycetemcomitans nor S. mutans degraded LL-37. Conclusions:1. P. gingivalis, a highly proteolytic oral pathogen associated with adult periodontitis, can digest LL-37. 2. Human saliva protects LL-37 from degradation by P. gingivalis.