Thymosin β(4) and β(10) in Sjögren’s syndrome: saliva proteomics and minor salivary glands expression

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(4), Tβ(4) sulfoxide, and Tβ(10). Immunostaining for Tβ(4) and Tβ(10) was performed on minor salivary glands of patients with pSS and ss. RESULTS: Tβ(4) levels were statistically higher in patients with pSS with respect to the other subgroups. Tβ(10) was detectable in 66.7 % of patients with pSS and in 42.8 % of those with ss/SSc, while Tβ(4) sulfoxide was detectable in 44.4 % of patients with pSS and in 42.9 % of those with ss/SSc. Tβ(10) and Tβ(4) sulfoxide were not detectable in patients without associated ss and in healthy control subjects. Regarding thymosin immunostaining, all patients had immunoreactivity for Tβ(10), and a comparable distribution pattern in the four different subgroups of patients was observed. Tβ(4) immunoreactivity 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 Tβ(4) sulfoxide and Tβ(10) salivary 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 Tβ(10) in acinar cells in the absence of any reactivity for Tβ(4). These findings, taken together, suggest a different role for Tβ(4) and Tβ(10) in patients with pSS who have ss and other autoimmune disease.