Low number of memory B cells in the salivary glands of patients with primary Sjögren's syndrome

Abstract

We have previously shown that patients with primary Sjögren's Syndrome (pSS) show a significant reduction of autoantigen specific CD27+ memory B cells and an abnormally elevated level of autoantibody producing plasma cells in peripheral blood (PB) compared to controls. Because both memory B cells and plasma cells have been detected in salivary glands (SG) of pSS patients, we aimed to study the B cell pattern in SG biopsies. Double immunohistochemical staining of CD20 and CD27 was carried out on paraffin-embedded SG tissue from 10 pSS patients to distinguish CD20+/CD27+ memory B cells, and identify the CD20+ glandular B cell zones (BCZ). Given that plasma blasts and plasma cells are CD27++ and CD20− , additional CD138 single staining of serial sections allowed the distinction of CD27++/CD138− plasma blasts located within the BCZ from CD27++/CD138+ plasma cells that were found mostly on the periphery of the BCZ and also observed interstitially. Both BCZ and the memory B cell populations were then quantified. Contrary to what has been reported earlier through immunoflourescent staining of memory B cells in SG tissue, we have shown that there is a low number of memory B cells located within the glandular BCZ. Plasma blasts and plasma cells, however, were more abundant in the SG. Together our findings suggest that these low numbers of memory B cells in both PB and SG of pSS patients may be the result of activation of these cells into plasma cells at the site of inflammation.