Objective: The use of rituximab in vasculitis has increased interest in B cell biology. A subpopulation of B cells expressing CD25 shows antigen-presenting properties and may have regulatory functions. We assessed subpopulations of B cell maturation (Bm) and markers related to activity and antigen presentation, and related the findings to disease activity.
Methods: Multiparameter flow cytometry was used to assess numbers and proportions of circulating lymphocytes from 34 patients with vasculitis (16 remission, 18 active) and 20 controls.
Results: Active vasculitis samples showed decreased proportions of Bm1 (7.8% vs 11%; p = 0.041), Bm2' (0.2% vs 0.7%; p = 0.002), and Bm3/Bm4 (0.1% vs 0.3%; p = 0.006), compared with controls; Bm2 cells were the most frequently occurring B cells but they were not significantly different in active vasculitis (74% vs 62%; p = 0.083). In patients with remission the proportion of CD25+ B cells was increased compared to controls (48% vs 29%, respectively; p = 0.006) and also compared to active vasculitis (23%; p = 0.006). The proportion of CD86+ B cells was also increased (31%) compared to active vasculitis (8%; p = 0.001), and to controls (6%; p = 0.0003). In multivariate analysis, Bm2' cells and CD25+27- B cells were independently influencing the patient group.
Conclusion: In active vasculitis, a lower proportion of Bm1 cells may indicate activated B cells. Patients in remission had higher proportions of CD25+ (α-chain of interleukin 2 receptor) and CD86+ (costimulatory molecule) B cells. We suggest that these B cells may have a regulatory role, or alternatively may result from previous treatment.