High throughput screening identifies repurposable drugs for modulation of innate and acquired immune responses.

A balanced immune system is essential to maintain adequate host defense and effective self-tolerance. While an immune system that fails to generate appropriate response will permit infections to develop, uncontrolled activation may lead to autoinflammatory or autoimmune diseases. To identify drug candidates capable of modulating immune cell functions, we screened 1200 small molecules from the Prestwick Chemical Library for their property to inhibit innate or adaptive immune responses. Our studies focused specifically on drug interactions with T cells, B cells, and polymorphonuclear leukocytes (PMNs). Candidate drugs that were validated in vitro were examined in preclinical models to determine their immunomodulatory impact in chronic inflammatory diseases, here investigated in chronic inflammatory skin diseases. Using this approach, we identified several candidate drugs that were highly effective in preclinical models of chronic inflammatory disease. For example, we found that administration of pyrvinium pamoate, an FDA-approved over-the-counter anthelmintic drug, suppressed B cell activation in vitro and halted the progression of B cell-dependent experimental pemphigoid by reducing numbers of autoantigen-specific B cell responses. In addition, in studies performed in gene-deleted mouse strains provided additional insight into the mechanisms underlying these effects, for example, the receptor-dependent actions of tamoxifen that inhibit immune-complex-mediated activation of PMNs. Collectively, our methods and findings provide a vast resource that can be used to identify drugs that may be repurposed and used to promote or inhibit cellular immune responses.

MHC haplotype and B cell autoimmunity: Correlation with pathogenic IgG autoantibody subclasses and Fc glycosylation patterns.

Genome-wide association studies (GWAS) have identified many genes that are associated with the development of certain autoimmune disorders, but the MHC haplotypes still represent the most prevalent genetic risk factor for many autoimmune diseases. The mechanisms by which MHC-associated genetic susceptibility translates into B cell autoimmunity and the development of autoimmune diseases are complex. There is increasing evidence that the MHC haplotype modulates autoreactive B cell responses in multiple ways. Instead of merely inhibiting the production of IgG autoantibodies and mediating complete immunological tolerance, the non-permitting MHC haplotypes seem to facilitate the production of IgG autoantibodies exhibiting Fc glycosylation patterns that are associated with reduced pathogenicity and a protective cytokine profile of T follicular helper (Tfh) cells. Here, we discuss mechanisms linking MHC haplotypes to the production of pathogenic IgG autoantibodies, which could be relevant for the development of improved diagnosis, particularly in the context of individual medicine.

IgG Fc sialylation is regulated during the germinal center reaction following immunization with different adjuvants.

BACKGROUND: Effector functions of IgG Abs are regulated by their Fc N-glycosylation pattern. IgG Fc glycans that lack galactose and terminal sialic acid residues correlate with the severity of inflammatory (auto)immune disorders and have also been linked to protection against viral infection and discussed in the context of vaccine-induced protection. In contrast, sialylated IgG Abs have shown immunosuppressive effects. OBJECTIVE: We sought to investigate IgG glycosylation programming during the germinal center (GC) reaction following immunization of mice with a foreign protein antigen and different adjuvants. METHODS: Mice were analyzed for GC T-cell, B-cell, and plasma cell responses, as well as for antigen-specific serum IgG subclass titers and Fc glycosylation patterns. RESULTS: Different adjuvants induce distinct IgG+ GC B-cell responses with specific transcriptomes and expression levels of the α2,6-sialyltransferase responsible for IgG sialylation that correspond to distinct serum IgG Fc glycosylation patterns. Low IgG Fc sialylation programming in GC B cells was overall highly dependent on the Foxp3- follicular helper T (TFH) cell-inducing cytokine IL-6, here in particular induced by water-in-oil adjuvants and Mycobacterium tuberculosis. Furthermore, low IgG Fc sialylation programming was dependent on adjuvants that induced IL-27 receptor-dependent IFN-γ+ TFH1 cells, IL-6/IL-23-dependent IL-17A+ TFH17 cells, and high ratios of TFH cells to Foxp3+ follicular regulatory T cells. Here, the 2 latter were dependent on M tuberculosis and its cord factor. CONCLUSION: This study's findings regarding adjuvant-dependent GC responses and IgG glycosylation programming may aid in the development of novel vaccination strategies to induce IgG Abs with both high affinity and defined Fc glycosylation patterns in the GC.

Dual Role of Interleukin-10 in Murine NZB/W F1 Lupus.

As a key anti-inflammatory cytokine, IL-10 is crucial in preventing inflammatory and autoimmune diseases. However, in human and murine lupus, its role remains controversial. Our aim was to understand regulation and immunologic effects of IL-10 on different immune functions in the setting of lupus. This was explored in lupus-prone NZB/W F1 mice in vitro and vivo to understand IL-10 effects on individual immune cells as well as in the complex in vivo setting. We found pleiotropic IL-10 expression that largely increased with progressing lupus, while IL-10 receptor (IL-10R) levels remained relatively stable. In vitro experiments revealed pro- and anti-inflammatory IL-10 effects. Particularly, IL-10 decreased pro-inflammatory cytokines and slowed B cell proliferation, thereby triggering plasma cell differentiation. The frequent co-expression of ICOS, IL-21 and cMAF suggests that IL-10-producing CD4 T cells are important B cell helpers in this context. In vitro and in vivo effects of IL-10 were not fully concordant. In vivo IL-10R blockade slightly accelerated clinical lupus manifestations and immune dysregulation. Altogether, our side-by-side in vitro and in vivo comparison of the influence of IL-10 on different aspects of immunity shows that IL-10 has dual effects. Our results further reveal that the overall outcome may depend on the interplay of different factors such as target cell, inflammatory and stimulatory microenvironment, disease model and state. A comprehensive understanding of such influences is important to exploit IL-10 as a therapeutic target.

In Vivo Expansion of Endogenous Regulatory T Cell Populations Induces Long-Term Suppression of Contact Hypersensitivity.

Contact hypersensitivity (CHS) of murine skin serves as a model of allergic contact dermatitis. Hapten-specific CD8 T cells and neutrophils represent the major effector cells driving this inflammatory reaction whereas Foxp3(+) regulatory T cells (Tregs) control the severity of inflammation. However, whether in vivo expansion of endogenous Tregs can downregulate CHS-mediated inflammation remains to be elucidated. In this study, we addressed this issue by using injection of an IL-2/anti-IL-2 mAb JES6-1 complex (IL-2/JES6-1) as a means of Treg induction in 2,4,6-trinitrochlorobenzene-induced CHS. IL-2/JES6-1 injection before or after hapten sensitization led to a considerable reduction of skin inflammation, even when rechallenged up to 3 wk after the last treatment. Conversely, Treg depletion re-established the CHS response in IL-2/JES6-1-treated mice. IL-2/JES6-1 injection resulted in increased frequencies of natural and peripheral Tregs in spleen and draining lymph nodes (LNs), elevated IL-10 and TGF-ß production by CD4 T cells, reduced CD86 expression by dendritic cells, and led to lower numbers of hapten-specific IFN-γ-producing CD8 T effector cells in LNs. Neutrophil and CD8 T cell infiltration was reduced in inflamed ear tissue, whereas CTLA-4(+)Foxp3(+) Treg frequencies were augmented. Adoptive transfer of LN cells of sensitized mice into recipients treated with IL-2/JES6-1 showed impaired CHS. Our results show that in vivo Treg expansion results in a prolonged CHS suppression, a sustained reduction of hapten-specific CD8 T cells, and a decrease in effector cell influx in inflamed tissue.

Artery Tertiary Lymphoid Organs Control Multilayered Territorialized Atherosclerosis B-Cell Responses in Aged ApoE-/- Mice.

OBJECTIVE: Explore aorta B-cell immunity in aged apolipoprotein E-deficient (ApoE(-/-)) mice. APPROACH AND RESULTS: Transcript maps, fluorescence-activated cell sorting, immunofluorescence analyses, cell transfers, and Ig-ELISPOT (enzyme-linked immunospot) assays showed multilayered atherosclerosis B-cell responses in artery tertiary lymphoid organs (ATLOs). Aging-associated aorta B-cell-related transcriptomes were identified, and transcript atlases revealed highly territorialized B-cell responses in ATLOs versus atherosclerotic lesions: ATLOs showed upregulation of bona fide B-cell genes, including Cd19, Ms4a1 (Cd20), Cd79a/b, and Ighm although intima plaques preferentially expressed molecules involved in non-B effector responses toward B-cell-derived mediators, that is, Fcgr3 (Cd16), Fcer1g (Cd23), and the C1q family. ATLOs promoted B-cell recruitment. ATLO B-2 B cells included naive, transitional, follicular, germinal center, switched IgG1(+), IgA(+), and IgE(+) memory cells, plasmablasts, and long-lived plasma cells. ATLOs recruited large numbers of B-1 cells whose subtypes were skewed toward interleukin-10(+) B-1b cells versus interleukin-10(-) B-1a cells. ATLO B-1 cells and plasma cells constitutively produced IgM and IgG and a fraction of plasma cells expressed interleukin-10. Moreover, ApoE(-/-) mice showed increased germinal center B cells in renal lymph nodes, IgM-producing plasma cells in the bone marrow, and higher IgM and anti-MDA-LDL (malondialdehyde-modified low-density lipoprotein) IgG serum titers. CONCLUSIONS: ATLOs orchestrate dichotomic, territorialized, and multilayered B-cell responses in the diseased aorta; germinal center reactions indicate generation of autoimmune B cells within the diseased arterial wall during aging.

IL-10 mediates plasmacytosis-associated immunodeficiency by inhibiting complement-mediated neutrophil migration.

BACKGROUND: Plasmacytosis (ie, an expansion of plasma cell populations to much greater than the homeostatic level) occurs in the context of various immune disorders and plasma cell neoplasia. This condition is often associated with immunodeficiency that causes increased susceptibility to severe infections. Yet a causative link between plasmacytosis and immunodeficiency has not been established. OBJECTIVE: Because recent studies have identified plasma cells as a relevant source of the immunosuppressive cytokine IL-10, we sought to investigate the role of IL-10 during conditions of polyclonal and neoplastic plasmacytosis for the regulation of immunity and its effect on inflammation and immunodeficiency. METHODS: We used flow cytometry, IL-10 reporter (Vert-X) and B cell-specific IL-10 knockout mice, migration assays, and antibody-mediated IL-10 receptor blockade to study plasmacytosis-associated IL-10 expression and its effect on inflammation and Streptococcus pneumoniae infection in mice. ELISA was used to quantify IL-10 levels in patients with myeloma. RESULTS: IL-10 production was a common feature of normal and neoplastic plasma cells in mice, and IL-10 levels increased with myeloma progression in patients. IL-10 directly inhibited neutrophil migration toward the anaphylatoxin C5a and suppressed neutrophil-dependent inflammation in a murine model of autoimmune disease. MOPC.315.BM murine myeloma leads to an increased incidence of bacterial infection in the airways, which was reversed after IL-10 receptor blockade. CONCLUSION: We provide evidence that plasmacytosis-associated overexpression of IL-10 inhibits neutrophil migration and neutrophil-mediated inflammation but also promotes immunodeficiency.

B cells, dendritic cells, and macrophages are required to induce an autoreactive CD4 helper T cell response in experimental epidermolysis bullosa acquisita.

In autoimmune bullous dermatoses (AIBD), autoantibodies induce blisters on skin or mucous membranes, or both. Mechanisms of continued autoantibody production and blistering have been well characterized using AIBD animal models. Mechanisms leading to the initial autoantibody production, however, have not been investigated in detail. Epidermolysis bullosa acquisita (EBA) is an AIBD associated with autoantibodies to type VII collagen (COL7). The majority of EBA patients' sera recognize the noncollagenous domain 1, including the von Willebrand factor A-like domain 2 (vWFA2). In experimental EBA induced by immunization with GST-COL7, disease manifestation depended on the genetic background, a Th1 polarization, and the GST-tag. In this model, nude mice neither produced autoantibodies nor blisters. It has remained uncertain which APC and T cell subsets are required for EBA induction. We established a novel EBA model by immunization with vWFA2 fused to intein (lacking the GST-tag). All tested mouse strains developed autoantibodies, but blisters were exclusively observed in mice carrying H2s. In immunized mice, CD4 T cells specific for vWFA2 were detected, and their induction required presence of B cells, dendritic cells, and macrophages. Anti-vWFA2 autoantibodies located at the lamina densa bound to the dermal side of salt-split skin and induced blisters when transferred into healthy mice. Absence of CD8 T cells at time of immunization had no effect, whereas depletion of CD4 T cells during the same time period delayed autoantibody production and blisters. Collectively, we demonstrate the pathogenic relevance of Abs targeting the vWFA2 domain of COL7 and show the requirement of APC-induced CD4 T cells to induce experimental EBA.

CD8 T cells induce T-bet-dependent migration toward CXCR3 ligands by differentiated B cells produced during responses to alum-protein vaccines.

Antibody-forming cells (AFCs) expressing the chemokine receptor CXCR3 are recruited to sites of inflammation where they help clear pathogens but may participate in autoimmune diseases. Here we identify a mechanism that induces CXCR3 expression by AFC and germinal center (GC) B cells. This happens when CD8 T cells are recruited into CD4 T cell-dependent B-cell responses. Ovalbumin-specific CD4 T cells (OTII) were transferred alone or with ovalbumin-specific CD8 T cells (OTI) and the response to subcutaneous alum-precipitated ovalbumin was followed in the draining lymph nodes. OTII cells alone induce T helper 2-associated class switching to IgG1, but few AFC or GC B cells express CXCR3. By contrast, OTI-derived IFN-γ induces most responding GC B cells and AFCs to express high levels of CXCR3, and diverse switching to IgG2a, IgG2b, with some IgG1. Up-regulation of CXCR3 by GC B cells and AFCs and their migration toward its ligand CXCL10 are shown to depend on B cells' intrinsic T-bet, a transcription factor downstream of the IFN-γR signaling. This model clarifies how precursors of long-lived AFCs and memory B cells acquire CXCR3 that causes their migration to inflammatory foci.

Immunomodulatory effects of heat shock protein 90 inhibition on humoral immune responses.

Heat shock protein 90 (Hsp90) inhibition blocks T-cell-linked inflammatory disease pathways and exhibits therapeutic activity in autoimmune disease mouse models, including the blistering disease epidermolysis bullosa acquisita. Although we previously showed that preformed autoreactive plasma cells do not seem to be directly affected by anti-Hsp90 treatment, immunomodulatory effects of Hsp90 inhibition on (auto-)antibody responses are not yet fully understood. In this study, the Hsp90 blocker 17-DMAG inhibited proliferation of activated total B cells and their IgG secretion in cultures of human peripheral B cells from healthy subjects, but IgG production was no longer affected when these activated B cells were allowed to differentiate prior to a deferred application of the inhibitor. 17-DMAG treatment was associated with induction of nuclear and cytoplasmic heat shock factor 1 and Hsp70 in stimulated human B cells, respectively. Type VII collagen (epidermolysis bullosa acquisita)-immunized mice early treated with 17-DMAG had reduced total B cells in spleens, a relative increase in splenic regulatory B cell fractions, higher serum IL-10 concentrations, and lower levels of circulating autoantibodies (paralleled by less pronounced disease induction) compared with vehicle-treated immunized mice. Autoantibody production was blunted in isolated and autoantigen-restimulated lymph node cells from immunized mice by either 17-DMAG or purified autologous splenic regulatory B cells. Thus, in addition to the previously described T cell inhibitory effects of Hsp90 blockade, this treatment potently modulates humoral immune responses at the B cell level, further supporting the introduction of Hsp90 inhibitors into the clinical setting for treatment of autoantibody-mediated disorders.

Heat-shock protein 90 inhibition in autoimmunity to type VII collagen: evidence that nonmalignant plasma cells are not therapeutic targets.

Blocking heat-shock protein 90 (Hsp90) induces death of malignant plasma cells by activation of the unfolded protein response, a signaling pathway activated by accumulation of misfolded proteins within the endoplasmic reticulum. We hypothesized that nontransformed plasma cells are also hypersensitive to Hsp90 inhibition because of their high amount of protein biosynthesis. To investigate this hypothesis, 2 different Hsp90 inhibitors, the geldanamycin derivative 17-DMAG and the nontoxic peptide derivative TCBL-145, were applied to mice with experimental epidermolysis bullosa acquisita, an autoimmune bullous disease characterized by autoantibodies against type VII collagen of the dermal-epidermal junction. Both inhibitors ameliorated clinical disease of type VII collagen-immunized mice, suppressed auto-antibody production, and reduced dermal neutrophilic infiltrate. Interestingly, total plasma cell numbers, type VII collagen-specific plasma cells, and germinal center B cells were unaffected by anti-Hsp90 treatment in vivo. However, T-cell proliferation was potently inhibited, as evidenced by the reduced response of isolated lymph node cells from immunized mice to in vitro restimulation with anti-CD3/CD28 antibody or autoantigen in the presence of Hsp90 inhibitors. Our results suggest that Hsp90 blockade has no impact on normal or autoreactive plasma cells in vivo and indentify T cells as targets of anti-Hsp90 treatment in autoimmunity to type VII collagen.

CXCR3 promotes the production of IgG1 autoantibodies but is not essential for the development of lupus nephritis in NZB/NZW mice.

OBJECTIVE: Autoantibody immune complexes and cellular infiltrates drive nephritis in patients with systemic lupus erythematosus (SLE) and in murine lupus. The chemokine receptor CXCR3 is assumed to promote cellular infiltration of inflamed tissues. Moreover, CXCR3 deficiency ameliorates lupus nephritis in the MRL/MpJ-Fas(lpr) (MRL/lpr) mouse model of SLE. Hence, CXCR3 blockade has been suggested as a novel therapeutic strategy for the treatment of lupus nephritis. We undertook this study to test the effect of CXCR3 in the (NZB × NZW)F(1) (NZB/NZW) mouse model of SLE. METHODS: CXCR3(-/-) NZB/NZW mice were generated and monitored for survival, proteinuria, and kidney infiltration. Anti-double-stranded DNA (anti-dsDNA) and total IgG1, IgG2a, and IgG2b antibody levels were determined by enzyme-linked immunosorbent assay. T cell and plasma cell infiltrates in the kidneys and interferon-γ production were determined by flow cytometry. Plasma cell infiltrates were measured using enzyme-linked immunospot assay. Kidney tissue was evaluated for pathologic changes. RESULTS: CXCR3(-/-) NZB/NZW mice exhibited reduced production of total and anti-dsDNA antibodies of the IgG1 subclass, but had normal titers of IgG2a and IgG2b antibodies compared to CXCR3(+/+) NZB/NZW mice. Cellular infiltrates and glomerulonephritis were not reduced in CXCR3(-/-) mice. CONCLUSION: CXCR3 has an effect on (auto)antibody production but is not essential for lupus pathogenesis in NZB/NZW mice, indicating that the effect of CXCR3 on the development of kidney disease varies between MRL/lpr and NZB/NZW mice. These results suggest that CXCR3-dependent and -independent mechanisms can mediate lupus nephritis. Hence, therapeutic CXCR3 blockade could be beneficial for only a subgroup of patients with SLE.

Proteasome inhibition with bortezomib depletes plasma cells and autoantibodies in experimental autoimmune myasthenia gravis.

Bortezomib, an inhibitor of proteasomes, has been reported to reduce autoantibody titers and to improve clinical condition in mice suffering from lupus-like disease. Bortezomib depletes both short- and long-lived plasma cells; the latter normally survive the standard immunosuppressant treatments targeting T and B cells. These findings encouraged us to test whether bortezomib is effective for alleviating the symptoms in the experimental autoimmune myasthenia gravis (EAMG) model for myasthenia gravis, a disease that is characterized by autoantibodies against the acetylcholine receptor (AChR) of skeletal muscle. Lewis rats were immunized with saline (control, n = 36) or Torpedo AChR (EAMG, n = 54) in CFA in the first week of an experimental period of 8 wk. After immunization, rats received twice a week s.c. injections of bortezomib (0.2 mg/kg in saline) or saline injections. Bortezomib induced apoptosis in bone marrow cells and reduced the amount of plasma cells in the bone marrow by up to 81%. In the EAMG animals, bortezomib efficiently reduced the rise of anti-AChR autoantibody titers, prevented ultrastructural damage of the postsynaptic membrane, improved neuromuscular transmission, and decreased myasthenic symptoms. This study thus underscores the potential of the therapeutic use of proteasome inhibitors to target plasma cells in Ab-mediated autoimmune diseases.

The B Cell Response and Formation of Allergenic and Anti-Allergenic Antibodies in Food Allergy.

Food allergies are a growing public health concern worldwide, especially in children and young adults. Allergen-specific IgE plays a central role in the pathogenesis of food allergies, but their titers poorly correlate with allergy development. Host immune systems yield allergen-specific immunoglobulin (Ig)A, IgE and IgG subclasses with low or high affinities and differential Fc N-glycosylation patterns that can affect the allergic reaction to food in multiple ways. High-affinity IgE is required to induce strong mast cell activation eventually leading to allergic anaphylaxis, while low-affinity IgE can even inhibit the development of clinically relevant allergic symptoms. IgA and IgG antibodies can inhibit IgE-mediated mast cell activation through various mechanisms, thereby protecting IgE-positive individuals from allergy development. The production of IgE and IgG with differential allergenic potential seems to be affected by the signaling strength of individual B cell receptors, and by cytokines from T cells. This review provides an overview of the diversity of the B cell response and the diverse roles of antibodies in food allergy.

Tissue-resident B cells orchestrate macrophage polarisation and function.

B cells play a central role in humoral immunity but also have antibody-independent functions. Studies to date have focused on B cells in blood and secondary lymphoid organs but whether B cells reside in non-lymphoid organs (NLO) in homeostasis is unknown. Here we identify, using intravenous labeling and parabiosis, a bona-fide tissue-resident B cell population in lung, liver, kidney and urinary bladder, a substantial proportion of which are B-1a cells. Tissue-resident B cells are present in neonatal tissues and also in germ-free mice NLOs, albeit in lower numbers than in specific pathogen-free mice and following co-housing with 'pet-store' mice. They spatially co-localise with macrophages and regulate their polarization and function, promoting an anti-inflammatory phenotype, in-part via interleukin-10 production, with effects on bacterial clearance during urinary tract infection. Thus, our data reveal a critical role for tissue-resident B cells in determining the homeostatic 'inflammatory set-point' of myeloid cells, with important consequences for tissue immunity.

Autoimmune pre-disease.

Approximately 5% of the world-wide population is affected by autoimmune diseases. Overall, autoimmune diseases are still difficult to treat, impose a high burden on patients, and have a significant economic impact. Like other complex diseases, e.g., cancer, autoimmune diseases develop over several years. Decisive steps in the development of autoimmune diseases are (i) the development of autoantigen-specific lymphocytes and (often) autoantibodies and (ii) potentially clinical disease manifestation at a later stage. However, not all healthy individuals with autoantibodies develop disease manifestations. Identifying autoantibody-positive healthy individuals and monitoring and inhibiting their switch to inflammatory autoimmune disease conditions are currently in their infancy. The switch from harmless to inflammatory autoantigen-specific T and B-cell and autoantibody responses seems to be the hallmark for the decisive factor in inflammatory autoimmune disease conditions. Accordingly, biomarkers allowing us to predict this progression would have a significant impact. Several factors, such as genetics and the environment, especially diet, smoking, exposure to pollutants, infections, stress, and shift work, might influence the progression from harmless to inflammatory autoimmune conditions. To inspire research directed at defining and ultimately targeting autoimmune predisease, here, we review published evidence underlying the progression from health to autoimmune predisease and ultimately to clinically manifest inflammatory autoimmune disease, addressing the following 3 questions: (i) what is the current status, (ii) what is missing, (iii) and what are the future perspectives for defining and modulating autoimmune predisease.

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.

Megakaryocytes constitute a functional component of a plasma cell niche in the bone marrow.

Long-lived plasma cells in the bone marrow produce memory antibodies that provide immune protection persisting for decades after infection or vaccination but can also contribute to autoimmune and allergic diseases. However, the composition of the microenvironmental niches that are important for the generation and maintenance of these cells is only poorly understood. Here, we demonstrate that, within the bone marrow, plasma cells interact with the platelet precursors (megakaryocytes), which produce the prominent plasma cell survival factors APRIL (a proliferation-inducing ligand) and IL-6 (interleukin-6). Accordingly, reduced numbers of immature and mature plasma cells are found in the bone marrow of mice deficient for the thrombopoietin receptor (c-mpl) that show impaired megakaryopoiesis. After immunization, accumulation of antigen-specific plasma cells in the bone marrow is disturbed in these mice. Vice versa, injection of thrombopoietin allows the accumulation and persistence of a larger number of plasma cells generated in the course of a specific immune response in wild-type mice. These results demonstrate that megakaryocytes constitute an important component of the niche for long-lived plasma cells in the bone marrow.

Long-term bortezomib treatment reduces allergen-specific IgE but fails to ameliorate chronic asthma in mice.

BACKGROUND: Allergen-specific immunoglobulin (Ig) E initiates the effector cascade of allergic asthma and has been identified as a valuable target for therapeutic treatment of this disease. The proteasome inhibitor bortezomib was previously shown to deplete Ig-secreting plasma cells and to efficiently suppress Ig serum titers. The present study aimed at evaluating the therapeutic potential of the proteasome inhibitor bortezomib in allergic bronchial asthma. METHODS: To address this question, a chronic experimental asthma mouse model was used in a therapeutic setting. Mice were sensitized to ovalbumin (OVA) and challenged with OVA aerosol for 12 weeks. After 6 weeks of challenge, bortezomib treatment was started and continued for 1 week (short-term) or 6 weeks (long-term) with a dosage of 0.75 mg/kg body weight twice a week. Lung function, lung histology, Ig serum titers and plasma cell numbers were assessed. RESULTS: Whereas short-term treatment lowered bronchoalveolar lavage eosinophils, long-term treatment considerably reduced serum titers of anti-OVA IgE in mice with chronic experimental asthma. However, neither short-term nor long-term treatment significantly reduced plasma cell numbers, anti-OVA IgG1 serum titers or allergic airway inflammation or ablated airway hyperresponsiveness. CONCLUSION: Our results suggest that bortezomib treatment has only limited value as plasma cell-depleting therapy against allergic bronchial asthma.

Myeloperoxidase-specific plasma cell depletion by bortezomib protects from anti-neutrophil cytoplasmic autoantibodies-induced glomerulonephritis.

Anti-neutrophil cytoplasmic autoantibodies (ANCA) cause vasculitis and necrotizing crescentic glomerulonephritis (NCGN). Steroids and cytotoxic drugs reduce mortality but can cause significant adverse events. The proteasome inhibitor bortezomib (BTZ) prevents glomerulonephritis in mouse models of lupus but its efficacy in ANCA-associated glomerulonephritis is unknown. We induced anti-MPO IgG-mediated NCGN by transplanting wild-type bone marrow (BM) into irradiated MPO-deficient mice immunized with MPO. Four weeks after BM transplantation, we treated mice with steroid/cyclophosphamide (S/CYC) or BTZ. Compared with untreated control mice, both S/CYC and BTZ significantly reduced urine abnormalities, NCGN, and infiltration of neutrophils and macrophages. Response to BTZ depended on timing of administration: BTZ abrogated NCGN if begun 3 weeks, but not 5 weeks, after BM transplantation. BTZ treatment significantly reduced total and MPO-specific plasma cells in both the spleen and bone marrow, resulting in significantly reduced anti-MPO titers. Furthermore, BTZ affected neither B cells nor total CD4 and CD8 T cells, including their naive and effector subsets. In contrast, S/CYC reduced the total number of cells in the spleen, including total and MPO-specific plasma cells and B cells. In contrast to BTZ, S/CYC did not affect total and MPO-specific plasma cells in the bone marrow. Three of 23 BTZ-treated mice died within 36 hours after BTZ administration. In summary, BTZ depletes MPO-specific plasma cells, reduces anti-MPO titers, and prevents NCGN in mice.