The expression of APRIL in Sjögren's syndrome: aberrant expression of APRIL in the salivary gland

A proliferation-inducing ligand (APRIL) and B-cell activating factor (BAFF) are B-cell-related mediators and may play a role in the pathogenesis in SS. In this descriptive study we assessed the expression of APRIL and BAFF in the minor salivary gland and serum from SS patients. Paraffin-embedded minor salivary gland sections from SS patients, non-SS controls and healthy volunteers were analysed by immunohistochemistry. Digital image quantification was performed to evaluate the expression of BAFF, APRIL and transmembrane activator and CAML interactor. Furthermore, serum was analysed for soluble BAFF and APRIL levels by ELISA. All the data were also analysed for subjects with decreased and normal stimulated salivary flow independent of the classification. APRIL expression was lower in minor salivary gland biopsies from SS patients compared with healthy volunteers and to a lesser extent non-SS controls, whereas BAFF expression was similar in all groups. Soluble APRIL levels in serum were increased in SS patients and in subjects with decreased salivary flow independent of the classification. APRIL salivary gland tissue levels are decreased, suggesting that targeting this cytokine locally in the salivary glands would not benefit SS patients. Moreover, the discrepancy between local and systemic levels is striking and future research should assess this in more detail.