Alteration of B cell subsets and the receptor for B cell activating factor (BAFF) in paediatric patients with type 1 diabetes.

BACKGROUND: Lately, mounting evidence has shown that B cells play an important role in the pathogenesis of type 1 diabetes (T1D). Here, we present alterations in B cell subsets including BAFF receptor (BAFFR) expression in cohorts of patients with type 1 diabetes (T1D) and their relatives.

PATIENTS AND METHODS: B cells were studied in 438 patients with T1D (158 at disease onset and 280 with long-term disease), 136 first-degree relatives and 53 healthy controls. The B cell panel included transitional, naïve, MZ-like, switched memory B cells and plasmablasts. We also measured serum BAFF levels as well as BAFFR expression on both B and T cells. Moreover, the effect of BAFF on T and B lymphocytes was analysed in vitro.

RESULTS: We observed a significant decrease in the proportion of transitional B cells in the patients with T1D, accompanied by an increased proportion of plasmablasts, especially in recent-onset patients and their relatives. While the BAFF serum levels did not differ in the patients with T1D, BAFFR-expressing B and especially T cell numbers were reduced in the T1D cohort, with the exception of patients with recent-onset disease who exhibited a significant increase in the number of BAFFR-expressing T cells. T cell activation and B cell proliferation were more pronounced after activation with BAFF in the T1D cohort compared to controls.

CONCLUSION: The B cell panel in patients with T1D is characterized by significantly reduced populations of B cells in their early stages of development with a shift towards plasma cells. The dynamics of BAFFR-expressing B and T cells and the more pronounced responsiveness of the T1D T cells to BAFF point to the role of BAFF and T and B cell cooperation in the development of T1D.