Salivary proteomics study measuring thymosin β4 and β10 expression in primary Sjögren's syndrome (pSS) versus other autoimmune diseases with and without sicca syndrome. TB4 and β10 were differentially expressed in saliva and minor salivary gland tissues across disease groups with distinct patterns in pSS versus secondary sicca syndrome. Proposes salivary thymosin β expression as a potential biomarker for differential diagnosis of pSS from other connective tissue diseases with overlapping dry eye and dry mouth symptoms.
Abstract
BACKGROUND: In the present study, we investigated whether thymosin β (Tβ) in saliva and in minor salivary glands is differentially expressed in patients with primary Sjögren's syndrome (pSS) and patients with autoimmune diseases (systemic sclerosis [SSc], systemic lupus erythematosus [SLE], and rheumatoid arthritis [RA], with and without sicca syndrome [ss]).
METHODS: Saliva specimens of nine patients with pSS, seven with ss/SSc, seven with ss/SLE, seven with ss/RA, seven with SSc, seven with SLE, and seven with RA, as well as ten healthy subjects, were analyzed using a high-performance liquid chromatograph coupled with a mass spectrometer equipped with an electrospray ionization source to investigate the presence and levels of Tβ, Tβsulfoxide, and Tβ. Immunostaining for Tβand Tβwas performed on minor salivary glands of patients with pSS and ss.
RESULTS: Tβlevels were statistically higher in patients with pSS with respect to the other subgroups. Tβwas detectable in 66.7 % of patients with pSS and in 42.8 % of those with ss/SSc, while Tβsulfoxide was detectable in 44.4 % of patients with pSS and in 42.9 % of those with ss/SSc. Tβand Tβsulfoxide were not detectable in patients without associated ss and in healthy control subjects. Regarding thymosin immunostaining, all patients had immunoreactivity for Tβ, and a comparable distribution pattern in the four different subgroups of patients was observed. Tβimmunoreactivity was present in patients with ss/SSc and those with ss/SLE, while it was completely absent in patients with pSS and those with ss/RA.
CONCLUSIONS: Our data show that higher salivary Tβ expression characterizes patients with pSS, while Tβsulfoxide and Tβsalivary expression was selectively present in patients with sicca symptoms. Moreover, at the immunohistochemical level in patients with pSS, minor salivary glands showed a peculiar pattern characterized by immunostaining for Tβin acinar cells in the absence of any reactivity for Tβ. These findings, taken together, suggest a different role for Tβand Tβin patients with pSS who have ss and other autoimmune disease.