Lectin binding studies of parotid salivary glycoproteins in Sjogren's syndrome

Human parotid salivas were collected from patients with secondary Sjogren's syndrome and controls without disease or with drug-induced xerostomia. Par otid glycoproteins were separated by gradient sodium dodecyl sulphate gel e lectrophoresis (SDS-PAGE), electroblotted onto nitrocellulose membrane and probed with biotinylated lectins of characterised sugar specificities. The binding patterns of lectins from Maclura pomifera (MPA) and Arachis hypogae a (PNA) indicated that many parotid glycoproteins have sialylated O-linked glycans and that sialylation is not affected by disease. Binding by lectins from Ricinus communis (RCA-1), Limax flavus (LFA), Lotus tetragonolobus (L TA) and Ulex europaeus (UEA-1) appeared unaltered in secondary Sjogren's sy ndrome, suggesting no obvious change in N-glycosylation of parotid glycopro teins. Variations in binding patterns of most lectins was attributable to s ubject-to-subject variations in recognised polymorphic proteins. Dolichos b iflorus agglutinin (DBA) consistently showed increased binding to a 75 kDa (M-r) protein in salivas from patients with secondary Sjogren's syndrome. T he binding protein was identified as lactoferrin but found not to contain N -acetylgalactosamine, the sugar to which DBA binds. Binding of DBA to lacto ferrin was dependent upon its saturation with iron, modified SDS-PAGE under nonreducing conditions resolved iron-free and iron-saturated lactoferrins and demonstrated increased levels of the iron-saturated form in secondary S jogren's syndrome. Lectin binding studies of purified lactoferrins from sal iva, milk, and polymorphonuclear neutrophils suggested that raised levels o f lactoferrin in saliva originate from salivary cells and not from inflamma tory cells. These results suggest that DBA binding provides greater specifi city as an indicator of salivary gland disease than measurement of lactofer rin levels alone.