A-fodrinAutoantigen Detection in Saliva and on Salivary Ductal Cells in Sjögren Syndrome

Background: Sjögren syndrome (SS) is an autoimmune exocrinopathy in which patients produce autoantibodies against the antigen α-fodrin. In the murine model the antigen that elicits the antibody response is a 120 kDa cleaved α-fodrin fragment. In a human salivary gland (HSG) ductal cell in vitro model the α-chain of the protein fodrin is cleaved following TNF-induced apoptosis to yield a cleaved product. Cleaved α-fodrin is presented on the cell surface suggesting a mechanism for antigen recognition in vivo as well as a potential antigen of value in diagnosis. The objective of this study was to test the hypothesis that cleaved α-fodrin is expressed in minor salivary gland biopsies and saliva in vivo . Methods: Nineteen patients with primary SS were recruited and provided plasma and a minor salivary gland biopsy. Nine of the 19 patients provided sufficient whole unstimulated saliva suitable for analysis. Saliva and minor salivary gland biopsies were also obtained from 16 healthy individuals without a history of autoimmune disease, and from 22 patients with HIV/AIDS. Biopsies were examined and graded histologically and with a monospecific antibody ( ASP 1185) for detection of the cleaved 120 kD fragment of α-fodrin by immunohistochemistry. Saliva was concentrated and subjected to Western blot analysis using an enhanced chemiluminescent detection system and by an antibody against the cleaved fragment of α-fodrin. Plasma was also tested for autoantibodies against cleaved α-fodrin using a commercially available ELISA. Results: Seventy nine percent of patient saliva samples were shown to contain a 120 kDa cleaved α-fodrin protein on ductal epithelia in the minor salivary glands and 4 of the same patients had detectable cleaved α-fodrin in saliva. None of the saliva samples or minor salivary gland biopsies from 16 healthy controls or from 22 patients with HIV/AIDS contained detectable cleaved α-fodrin protein. Conclusion: This is the first report of the cleaved 120 kDa fragment of the autoantigen α-fodrin in saliva. Confirmation in a larger number of patients at earlier stages of disease is necessary. Further studies could lead to the development of a diagnostic tool to monitor disease progression via a saliva sample.