The native human saliva obtained through the centrifugation of whole saliva showed characteristic salivary protein complex (SPC) peaks in gel filtration high performance liquid chromatography (HPLC) using Superose 12 column1,2). In the previous study the SPC peaks in chromatography were explored to know their composition and functions by different detection methods, but still the nature of SPCs was not clearly elucidated so far. In this study the SPC peaks were examined by direct antibody interaction in order to target different antimicrobial and protective proteins distributed in the SPCs via gel filtration HPLC. As the SPC peak shape and migration speed can be changed by antibody binding to specific proteins of SPC, it was found that mucin1 is evenly distribution in all SPCs, while PRPs are more abundant in the late dominant SPC than the early dominant SPC and also in the intermediated SPCs. Most of antimicrobial proteins including lysozyme, LL-37, lactoferrin, β-defensin-1, -2, -3, IgA, mucocidin, and α1-antitrypsin were more abundant in the late dominant SPC than the early dominant SPC, while histatin showed relatively even distribution in all SPCs. Therefore, it was presumed that the late dominant SPC containing abundant antimicrobial and protective proteins could be applied as a biomarker to measure the defensive potential of whole saliva in oral diseases.

In order to know the characteristic roles of salivary protein complex (SPC) the gel-filtration chromatography was performed using the unstimulated and the stimulated whole saliva separately. The first and second dominant SPC peaks were fractionated and analyzed by immunoprecipitation HPLC (IP-HPLC) using antibodies against the essential salivary proteins including α-amylase, mucin-1, proline rich proteins (PRPs), histatin, cystatin, LL-37, lysozyme, lactoferrin, -defensin-1, -2, -3, IgA, transglutaminase 4 (TGase 4), mucocidin, α1-antitrypsin, cathepsin G. In the gel-filtration chromatography the stimulated whole saliva showed much reduced amount of SPCs than the unstimulated whole saliva, but the proportional patterns of both whole saliva were almost similar each other. Through IP-HPLC analysis both of the first and second dominant SPCs were variably positive for the essential salivary proteins, however, α-amylase, mucin-1, PRPs, lysozyme, and cathepsin G were predominant in the first dominant SPC, while cystatin, lactoferrin, β-defensin-1, -2,-3, IgA, mucocidin, TGase 4, and α1-antitrypsin were predominant in the second dominant SPC. And more, the α1-antitrypsin and cathepsin G which were mostly derived from gingival crevicular fluid were also consistently found in the SPCs. These data may suggest that the first dominant SPC, rich in α-amylase, mucin-1, PRPs, lysozyme, and cathepsin G, may play a role in food digestion, protein degradation, and mucosa lubrication, while the second dominant SPC, rich in cystatin, lactoferrin, β-defensin-1, -2, -3, mucocidin, IgA, TGase 4, and α1-antitrypsin, may play a role in the mucosa protection and antimicrobial defense.

Salivary proteins include numerous functional proteins which play important roles not only for the food-intake but also for the protective and defensive mechanisms. In the present study the compositions of salivary proteins were analyzed by different methods, including electrophoresis and high performance liquid chromatography (HPLC). In hydrophobic protein HPLC analysis the parotid saliva gradually produced macromolecular complexes when agitated in refrigerator until 30 minutes. These salivary protein complexes were digested by neuraminidase, and then migrated more rapidly in native tris glycine gel than the control. Therefore, it was assumed that the glycosylated proteins of parotid saliva became gradually aggregated to form salivary protein complexes similar to those of whole saliva. The salivary protein complexes were easily degenerated in different experimental buffers, i.e., SDS buffer, tris glycine buffer, methanol, etc., and resulted non-specific patterns in electrophoresis and HPLC. Therefore, it was presumed that the salivary protein complexes was made by the hydrophobic interaction as well as electrostatic attraction between salivary proteins. These data indicated that to know the real pattern of salivary protein complexes in vivo the whole saliva should be analyzed by HPLC using non-adhering column with isoelectric buffer. Consequently, the whole saliva was analyzed by HPLC using reverse phase SuperoseTM column with 20 mM potassium phosphate buffer, and two prominent peaks of salivary protein complexes were consistently found in every people. These salivary protein complex peaks were relatively stable up to 6 hours after saliva collection when the whole saliva was kept in refrigerator during experiment. Therefore, it is suggested that the salivary protein complex patterns are characteristic macromolecular structures of whole saliva, which are also applicable as a diagnostic point in different saliva-associated diseases