Background B-lymphocytes are involved in the pathogenesis of ANCA-associated vasculitides (AAVs), but the knowledge about alterations in peripheral blood B-lymphocytes of AAV patients and the changes in B-lymphocyte subsets after immunosuppressive therapy is sparse. Alterations in B-cell subpopulations can shed light on AAVs pathogenesis and may guide treatment protocols. Immunosuppressive drugs like cyclophosphamide, azathioprine, and methotrexate, which constitute the prerequisite of a successful AAV therapy, may exert their beneficial effects by their influence on peripheral B-cell homeostasis and function. Using surface staining for CD19, CD20, CD27, IgM, IgD, CD38, and CD21, transitional B-cells, marginal zone B-cells, naive B-cells, class-switched memory B-cells (smBs), and plasmablasts can be identified.
Objectives To assess the effect of immunosuppressive therapies on peripheral B cell homeostasis and to investigate B cell repopulation after therapy with rituximab in patients with AAV.
Methods Staining and flow cytometric analysisof B cells was performed using a FACS Canto II. 5000 to 10000 B-cells were analyzed.
Results The B-cell compartment was analysed in 61 AAV patients. After immunosuppressive treatment B-lymphocytes and marginal zone B-cells (MZB) were persistently lowered. Low transitional B-cells (TR) indicated an impaired early B-lymphocyte development. B-lymphocytes and MZB were even decreased in patients with stable disease without immunosuppressive therapy. In untreated AAV patients the functionally exhausted CD21low-B-cells was expanded indicating an ongoing immunostimulatory process. Different from other autoimmune diseases like SLE plasmablasts were only slightly increased, showed no correlation to disease activity, and were efficiently targeted by immunosuppression. B-lymphocytes, MZB, TR, and plasmablasts correlated with immunoglobulin concentrations.
Seven patients were analysed for B-cell repopulation after RTX treatment. B-cell repopulation was analysed by measuring total B-cell numbers and transitional B-cells. Time from RTX to B-cell analysis ranged from 7 to 42 months in these patients. In 3 patients B-cell numbers were below 0.2% impeding a further detection of CD19+CD38+IgMhigh transitional B-cells because of paucity of events in the CD19 gate. In two of these patients time from RTX application to B-cell analysis was less than 12 months, but in one patient the absence of B-cells was observed 42 months after RTX therapy indicating a long-lasting effect on the B-cell compartment. In a further patient 0.17% transitional B-cells were measured, indicating an insufficient B-cell regeneration. Only two patients had moderately increased percentages of transitional B-cells, indicating a beginning recovery of the B-cell compartment 18 and 19 months after RTX, but absolute numbers of transitional B-cells were still low in these patients.
Conclusions Immunosuppression (IS) disturbs the B-cell compartment in AAV. Marginal zone B-cells (MZB) and transitional B-cells (TR) are decreased. Low MZB correlate with IgM levels. TR are reduced in AAV after immunosuppressive therapy, indicating an impaired early B-cell development. The reoccurrence of TR in AAV patients after RTX treatment is delayed. CD21 low B cells are expanded in AAVs.
Disclosure of Interest None Declared