Partial characterization of abnormal salivary proteins associated with rheumatoid arthritis

Isoelectric focusing of parotid saliva from 33 patients with rheumatoid arthritis but without clinical evidence of salivary gland involvement revealed multiple abnormal proteins of pI 3.95-4.25 in all cases, whereas only two out of 16 samples from normal healthy individuals exhibited any similar bands. Although rheumatoid factors of abnormally low isoelectric point and restricted heterogeneity were detected in this pI region in five of the diseased samples, these could not account for all of the bands even in these cases. The abnormal proteins did not otherwise cross-react with antisera to immunoglobulin (Ig) G, IgA or albumin. Analysis of rheumatoid arthritis parotid saliva by a method involving adsorption of rheumatoid factors to immobilized rabbit immunoglobulin revealed the presence of salivary rheumatoid factors (in seven patients) of all the major immunoglobulin classes, including secretory-IgA in two patients. Although these abnormal proteins are as yet uncharacterized, their presence could form the basis of a non-invasive procedure in the diagnosis of salivary gland and connective tissue disorders.