Objective: To examine the expression of surface structures important in natural killer (NK) cell function and the roles of serum factors affecting the expression of surface antigens on these cells in patients with Sjögren's syndrome (SS).
Methods: Peripheral blood mononuclear cells (PBMC) of 18 patients with SS were analyzed by immunofluorescence on a flow cytometer. The antigen recognized by autoantibodies in their sera was analyzed by immunofluorescence and by immunoprecipitation.
Results: Expression of Fcgamma receptor III (CD16), an important indicator of NK cytolytic activity, on PBMC was significantly decreased in patients with SS who have extraglandular disease, while the expression of Fcgamma RI and II was normal. Moreover, F(ab')2 of IgG in these patients' sera was shown to bind to CD16+ cells. Immunoprecipitation study showed that it bound to CD16 itself.
Conclusion: The depressed expression of CD16 on PBMC and the presence of antibody binding to CD16 in the patients' sera may be, at least in part, responsible for the altered function of NK cells observed in SS.