Mucins Provide an Anchoring Surface for Salivary Mucosal Pellicle Development

Objectives:  To investigate how mucins aid in salivary mucosal pellicle formation and whether or not transglutaminase (TGM) aids in protein cross-linking.

Methods:  HT29 and HT29-MTX cell lines, intestinal cell models, were used to compare protein binding to cell layers.  HT29-MTX cells secrete a layer of mucus containing MUC5AC whilst HT29 cells do not form mucus.  Whole mouth saliva (WMS) (+/-TGM), parotid saliva (PS) (+/-TGM) and sIgA (from human colostrum) were incubated for 20 or 60 minutes with cells at 4, 8 and 16 days of cell growth.  IgA ELISAs were used to compare IgA binding between saliva types, incubation times and cell types.  Western blotting was used to confirm salivary protein binding.

Results:  sIgA alone showed minimal binding to both cell types.  HT29-MTX cells with a pre-formed mucin (MUC5AC) layer, bound significantly more (P<0.05) IgA from WMS compared to HT29 cells.  IgA showed increased binding from PS to HT29-MTX cells where MUC5AC was present.  TGM made no difference to the binding of IgA to either cell type.

Conclusions:  Binding of IgA to epithelial cells appears to require other components of saliva and mucin provides a crucial anchoring layer.  This result confirms the complex model of salivary pellicle whereby mucins and globular proteins co-deposit on the oral surfaces in a synergistic fashion. 

Acknowledgments: This study was funded by a CASE studentship from the BBSRC and Unilever.