Saliva: a cell suspension of epithelial cells harboring the antimicrobial peptide LL-37 and the growth factor EGF

Sammanfattning: Saliva plays a crucial role in maintaining oral health through its physical and chemical properties that provide various protective functions. One of its essential components is the human host defense peptide LL-37, which is produced by immune cells and epithelial cells, and participates in the first line of defense against pathogens. LL-37 is a potent antimicrobial agent against both gram-positive and gram-negative bacteria, and furthermore it also modulates immune responses. Another important component of saliva is epidermal growth factor (EGF), which is produced by different cell types and acts as an essential stimulus of epithelial cell proliferation and differentiation, in wound healing and tissue repair. The levels of these peptides may be affected by various oral diseases. For instance, in periodontal disease, alterations in LL-37 and EGF contents and function have been observed in response to inflammation. The objective of the present doctoral thesis was to provide added information and insights into the salivary components LL-37 and EGF, and their functional importance by studying isolated human saliva from the major salivary glands, whole saliva, salivary glandular tissues, and cells in whole saliva. Multiple analyzing methods were used to quantify and visualize protein levels and cellular distribution of the peptides. The results demonstrated that all three major human salivary glands contributed to salivary hCAP18/LL-37 content of whole saliva, and immunohistochemistry applying co-localization analysis revealed that salivary hCAP18/LL-37 appears to originate from intravascular neutrophils. Furthermore, ELISA analysis showed that hCAP18/LL-37 was observed in both the cell-free and cell-containing proportions of human whole saliva, arguing that salivary cells also carry the peptide. Desquamated salivary epithelial cells expressed both hCAP18/LL-37 and EGF, proposing that these cells harbor both peptides and implying that the cells might play a prominent role in the innate immune response. The cells spontaneously released/leaked LL-37 into the extracellular medium, although its endogenous levels were too low to have an impact on S. mutans viability. Moreover, the findings revealed that whole saliva and cell-free saliva from caries-active subjects 18-23 years old contained similar amounts of hCAP18/LL-37 in comparison to controls. Interestingly, caries-active subjects with gingivitis displayed higher concentrations of hCAP18/LL-37 compared to caries-active subjects without gingivitis. In gingivitis, neutrophils are found in saliva, and since these cells are rich in hCAP18/LL-37, they probably contribute to the high levels of hCAP18/LL-37 found in saliva of these subjects. In conclusion, this thesis provides new knowledge and insights into the origin and function of hCAP18/LL-37 in human saliva, especially its distribution in different fractions of saliva, and the salivary concentration of hCAP18/LL-37 in subjects with dental caries and gingivitis. Moreover, we propose a novel functional importance of desquamated oral epithelial cells as carriers of hCAP18/LL-37 and EGF.