Salivary proteins in rheumatoid arthritis and Sjogren's syndrome: One-dimensional and two-dimensional electrophoretic studies

Parotid saliva from patients with rheumatoid arthritis and Sjogren's syndro me contains elevated levels of multiple anionic proteins of pl similar to 3 .75-4.75 and M-r similar to 32 000. Further studies on these components inv olving narrow range pH 3.5-5.0 immobilized pH gradients (IPGs) and two-dime nsional (2D) electrophoresis with narrow- or broad-range IPGs in the first dimension have confirmed their association with these disorders. Immunoblot ting showed that these proteins include multiple forms of tissue kallikrein . Treatment with neuraminidase results in removal of these anionic substanc es from the pH 3.75-4.75 region of gels, thereby indicating that heterogene ity arises from differences in sialation of the carbohydrate residues. The results of treatment with endo-PN-acetylglucosaminidase (Endo F) or peptide N-glycosidase (PNGase F) and comparison of the results with studies on hum an urinary kallikrein suggest that proteins other than kallikrein may also comigrate in the anionic region of gels and that deglycosylation of kallikr ien is incomplete in the experimental conditions used, probably because of inadequate denaturation; The paper also reviews the limitations of current criteria used in the investigation of salivary gland function associated wi th connective tissue disorders and the diagnosis of these. It assesses the potential of electrophoresis in forming the basis of new diagnostic techniq ues and furthering the understanding of the nature of these diseases. The f indings presented in this paper could make a key contribution to this.