CCL28 effects on periodontal pathogens

Chemokines are small proteins that signal to and attract cells of the immune system; they are vital components in the modulation of immunity and wound healing. A newly described chemokine was reported to have antibacterial and antifungal activity. This chemokine, chemokine (C-C motif) ligand 28 (CCL28; also called mucosae-associated epithelial chemokine), is secreted by mucosal epithelial cells and is found in saliva and in breast milk. The objective of this study was to test whether CCL28 has antibacterial activity against two anaerobic periodontal pathogens: Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans.

We used a bacterial viability test, in which two fluorescent dyes are bound differentially to living and killed bacteria. We tested the bacteria at concentrations of 2 x 10(7)/ml, exposing them to CCL28 at concentrations from 0.04 to 10 microM.

CCL28 was effective at killing both organisms. After 1 hour of exposure to the chemokine under appropriate oxygen conditions, the percentage of living organisms was reduced significantly for each species. We estimated the 50% effective concentration to be approximately 0.7 microM for P. gingivalis and approximately 2.0 microM for A. actinomycetemcomitans (N = five experiments each). We confirmed these observations using standard bacterial plating methods.

Because this chemokine is secreted into the saliva, a reduction in salivary flow (as in xerostomia) may diminish the oral self-defense mechanisms by also reducing the exposure of bacteria to the antibacterial action of CCL28.