Long-lived plasma cells are early and constantly generated in New Zealand Black/New Zealand White F1 mice and their therapeutic depletion requires a combined targeting of autoreactive plasma cells and their precursors.

INTRODUCTION: Autoantibodies contribute significantly to the pathogenesis of systemic lupus erythematosus (SLE). Unfortunately, the long-lived plasma cells (LLPCs) secreting such autoantibodies are refractory to conventional immunosuppressive treatments. Although generated long before the disease becomes clinically apparent, it remains rather unclear whether LLPC generation continues in the established disease. Here, we analyzed the generation of LLPCs, including autoreactive LLPCs, in SLE-prone New Zealand Black/New Zealand White F1 (NZB/W F1) mice over their lifetime, and their regeneration after depletion. METHODS: Bromodeoxyuridine pulse-chase experiments in mice of different ages were performed in order to analyze the generation of LLPCs during the development of SLE. LLPCs were enumerated by flow cytometry and autoreactive anti-double-stranded DNA (anti-dsDNA) plasma cells by enzyme-linked immunospot (ELISPOT). For analyzing the regeneration of LLPCs after depletion, mice were treated with bortezomib alone or in combination with cyclophosphamide and plasma cells were enumerated 12 hours, 3, 7, 11 and 15 days after the end of the bortezomib cycle. RESULTS: Autoreactive LLPCs are established in the spleen and bone marrow of SLE-prone mice very early in ontogeny, before week 4 and before the onset of symptoms. The generation of LLPCs then continues throughout life. LLPC counts in the spleen plateau by week 10, but continue to increase in the bone marrow and inflamed kidney. When LLPCs are depleted by the proteasome inhibitor bortezomib, their numbers regenerate within two weeks. Persistent depletion of LLPCs was achieved only by combining a cycle of bortezomib with maintenance therapy, for example cyclophosphamide, depleting the precursors of LLPCs or preventing their differentiation into LLPCs. CONCLUSIONS: In SLE-prone NZB/W F1 mice, autoreactive LLPCs are generated throughout life. Their sustained therapeutic elimination requires both the depletion of LLPCs and the inhibition of their regeneration.

Autoantibodies from long-lived 'memory' plasma cells of NZB/W mice drive immune complex nephritis.

OBJECTIVES: We have previously shown that both short- and long-lived plasma cells (PCs) significantly contribute to autoantibody production in NZB/W mice as a model of lupus nephritis. The aim of this study was to determine the role of autoreactive long-lived (memory) PCs refractory to immunosuppression and B cell depletion in the pathogenesis of systemic lupus erythematosus. METHODS: Splenic CD138+ antibody-secreting cells (ASCs) from >6-month-old NZB/W mice with high titres of anti-dsDNA autoantibodies or from Balb/c mice 5 days after secondary immunisation with ovalbumin (OVA) were adoptively transferred to immunodeficient Rag1(-/-) mice, in which the development of nephritis was investigated by measuring proteinuria. Total IgG and IgM as well as anti-dsDNA and anti-OVA antibody levels were followed up by ELISA. After 21 weeks the recipient mice were sacrificed so that PCs in spleen and bone marrow could be analysed using ELISPOT and flow cytometry and renal immunohistology performed. RESULTS: The adoptive transfer of NZB/W and anti-OVA ASCs resulted in the continuous generation of anti-dsDNA antibodies and anti-OVA antibodies, respectively, exclusively by long-lived PCs that had homed to the spleen and bone marrow of recipient Rag1(-/-) mice. Rag1(-/-) mice generating autoantibodies including anti-dsDNA had reduced survival, proteinuria and immune complex nephritis with C1q, C3, IgG and IgM deposits 21 weeks after transfer. CONCLUSIONS: These findings demonstrate that autoantibodies exclusively secreted by long-lived (memory) PCs contribute to autoimmune pathology and should be considered as candidate targets for future therapeutic strategies.

Bone marrow of NZB/W mice is the major site for plasma cells resistant to dexamethasone and cyclophosphamide: implications for the treatment of autoimmunity.

Antibodies contribute to the pathogenesis of many chronic inflammatory diseases, including autoimmune disorders and allergies. They are secreted by proliferating plasmablasts, short-lived plasma cells and non-proliferating, long-lived memory plasma cells. Memory plasma cells refractory to immunosuppression are critical for the maintenance of both protective and pathogenic antibody titers. Here, we studied the response of plasma cells in spleen, bone marrow and inflamed kidneys of lupus-prone NZB/W mice to high-dose dexamethasone and/or cyclophosphamide. BrdU+, dividing plasmablasts and short-lived plasma cells in the spleen were depleted while BrdU- memory plasma cells survived. In contrast, all bone marrow plasma cells including anti-DNA secreting cells were refractory to both drugs. Unlike bone marrow and spleen, which showed a predominance of IgM-secreting plasma cells, inflamed kidneys mainly accommodated IgG-secreting plasma cells, including anti-DNA secreting cells, some of which survived the treatments. These results indicate that the bone marrow is the major site of memory plasma cells resistant to treatment with glucocorticoids and anti-proliferative drugs, and that inflamed tissues and secondary lymphoid organs can contribute to the autoreactive plasma cell memory. Therefore, new strategies targeting autoreactive plasma cell memory should be considered. This could be the key to finding a curative approach to the treatment of chronic inflammatory autoantibody-mediated diseases.

Takayasu arteritis is characterised by disturbances of B cell homeostasis and responds to B cell depletion therapy with rituximab.

UNLABELLED: Introduction Takayasu arteritis (TA) is a large vessel vasculitis involving the aorta and its major branches. T cell-mediated autoimmunity is thought to play a major role in its pathogenesis, while the role of B cells is still unclear. METHODS: B cell subsets in the peripheral blood of 17 patients with TA were analysed and compared with nine patients with active systemic lupus erythematosus (SLE) and nine healthy controls by flow cytometry. Based on these findings, three patients with active refractory TA were treated with B cell depletion therapy (BCDT) using monoclonal anti-CD20 antibodies (rituximab). RESULTS: The absolute number and frequency of peripheral blood CD19(+)/CD20(-)/CD27(high) antibody-secreting cells in patients with active TA was significantly higher than in healthy donors. As in active SLE, the majority of these cells are newly generated plasmablasts which significantly correlated with TA activity. Three patients with active refractory TA and expansion of plasmablasts were successfully treated with BCDT, which resulted in remission. CONCLUSION: Disturbances of B cell homeostasis may be critical in TA. Circulating plasmablasts could be a useful biomarker of disease activity and a tool for selecting appropriate candidates for BCDT. B cells and plasmablasts/plasma cells may therefore represent novel targets for effective therapies for TA.