B cell hyperresponsiveness in Sjögren's syndrome.

We examined the production of and responsiveness to B cell growth factor (BCGF) by using proliferation assays in patients with Sjögren's syndrome (SS). We also studied the ability of SS B cells to respond to B cell stimulatory factors (BSF) by measuring the amount of IgG produced in vitro. SS patients showed normal production of and responsiveness to BCGF. They were also demonstrated to show a normal response to Staphylococcus aureus Cowan I (SAC). In addition, cell surface antigens of B cells in the peripheral blood of SS patients were not altered compared with normal controls. However, SS B cells produced a significant amount of IgG in vitro in response to BSF stimulation with or without anti-IgM antibody. Furthermore, there was a positive correlation between the hyperresponsiveness of B cells to BSF in vitro and serum IgG level in SS. We, therefore, suggest that the enhanced response of B cells to BSF might contribute to polyclonal B cell activation in SS.