Antimicrobial peptide LL‐37 and its pro‐form, hCAP18, in desquamated epithelial cells of human whole saliva

• Published in: European journal of oral sciences 2020-02, Vol.128 (1), p.1-6
• Main Authors: Aidoukovitch, Alexandra, Dahl, Sara, Fält, Felicia, Nebel, Daniel, Svensson, Daniel, Tufvesson, Ellen, Nilsson, Bengt‐Olof
• Format: Article
• Language: English
• Subjects: Antibodies; Antiinfectives and antibacterials; Antimicrobial agents; Antimicrobial peptides; Basic Medicine; Biologi; Biological Sciences; cathelicidin; Cathelicidins; Cell and Molecular Biology; Cell Biology; Cell- och molekylärbiologi; Cellbiologi; Centrifugation; Cytoplasm; Dentistry; Depolymerization; Dithiothreitol; Enzyme-linked immunosorbent assay; Epithelial Cells; host defense peptide; Humans; Immune system; Immunocytochemistry; Immunoreactivity; Innate immunity; Kallikrein; Light microscopy; Medical and Health Sciences; Medicin och hälsovetenskap; Medicinska och farmaceutiska grundvetenskaper; Molecular weight; Mucin; Mucins; Natural Sciences; Naturvetenskap; Optical microscopy; Peptides; Proteinase; Proteinase 3; Saliva; salivary fractions; Western blotting
• ISSN: 0909-8836; 1600-0722; 1600-0722
• DOI: 10.1111/eos.12664

The antimicrobial peptide LL‐37 is active against oral bacteria and has been demonstrated to be present in human saliva, but its distribution in different fractions of saliva is not known. LL‐37 is formed from its intracellular pro‐form, hCAP18, in an extracellular enzymatic reaction catalyzed by proteinase 3 and kallikrein 5. Here, we prepared cell‐containing and cell‐free fractions of unstimulated human whole saliva by centrifugation after depolymerization of mucins with dithiothreitol, and measured the levels of hCAP18/LL‐37 in these fractions using ELISA. Cellular expression of hCAP18/LL‐37 was determined by western blotting and immunocytochemistry. The ELISA analyses demonstrated that both cells and cell‐free saliva contained hCAP18/LL‐37. Western blot analysis of cell‐pellet homogenates showed a strong band corresponding to hCAP18 at the correct molecular weight and a weak band corresponding to LL‐37. Phase‐contrast and light microscopy revealed that the cells consisted of desquamated epithelial cells. These cells expressed cytoplasmic immunoreactivity for hCAP18/LL‐37. The peripheral part of the cytoplasm, corresponding to the plasma membrane, was particularly rich in hCAP18/LL‐37 immunoreactivity. No immunoreactivity was observed after omission of the primary antibody. We conclude that desquamated epithelial cells of human whole saliva contain antimicrobial hCAP18/LL‐37, suggesting that these cells may take part in the innate immune system by harboring and releasing these peptides.