Introduction:  During periodontitis, an innate immune response to bacterial challenge is primarily mediated by neutrophils. We compared neutrophilic content and the level of neutrophil‐derived antimicrobial peptides in gingival crevicular fluid (GCF) in two clinical forms of severe periodontitis.

Methods:  GCF was collected from 14 patients with aggressive periodontitis, 17 patients with chronic periodontitis, and nine healthy subjects. Samples were analyzed for periodontopathogen load using real‐time polymerase chain reactions. The amounts of myeloperoxidase and α‐defensins (HNP1–3) were determined by enzyme‐linked immunosorbent assay, and the level of cathelicidin (hCAP18/LL‐37) was assayed by Western blot.

Results:  Myeloperoxidase concentration was not correlated with levels of LL‐37 and HNP1–3 in samples from patients, compared to controls. The amount of HNP1–3 was twofold and fourfold higher in patients with aggressive and chronic periodontitis, respectively. Those with chronic disease had significantly elevated amounts of mature LL‐37. The increased concentration of both peptides in chronic periodontitis correlated with the load of Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola.

Conclusion:  The lack of a correlation between LL‐37, HNP1–3, and myeloperoxidase content suggests that neutrophils are not the sole source of these bactericidal peptides in the GCF of patients with periodontitis; and that other cells contribute to their local production. The bacterial proteases of P. gingivalis, T. forsythia, and T. denticola might degrade hCAP18/LL‐37, because the 11‐kDa cathelicidin‐derived fragment was present in GCF collected from pockets infected with these bacteria. Collectively, it appears that a local deficiency in LL‐37 can be considered as a supporting factor in the pathogenesis of severe cases of periodontitis.