Nobuko Ishiura

Regulatory B cells (B10 cells) have a suppressive role in murine lupus: CD19 and B10 cell deficiency exacerbates systemic autoimmunity.

B cells play critical roles in the pathogenesis of lupus. To examine the influence of B cells on disease pathogenesis in a murine lupus model, New Zealand Black and New Zealand White F1 hybrid (NZB/W) mice were generated that were deficient for CD19 (CD19−/− NZB/W mice), a B cell-specific cell surface molecule that is essential for optimal B cell signal transduction. The emergence of anti-nuclear Abs was significantly delayed in CD19−/− NZB/W mice compared with wild type NZB/W mice. However, the pathologic manifestations of nephritis appeared significantly earlier, and survival was significantly reduced in CD19−/− NZB/W mice compared with wild type mice. These results demonstrate both disease-promoting and protective roles for B cells in lupus pathogenesis. Recent studies have identified a potent regulatory B cell subset (B10 cells) within the rare CD1dhiCD5+ B cell subset of the spleen that regulates acute inflammation and autoimmunity through the production of IL-10. In wild type NZB/W mice, the CD1dhiCD5+B220+ B cell subset that includes B10 cells was increased by 2.5-fold during the disease course, whereas CD19−/− NZB/W mice lacked this CD1dhiCD5+ regulatory B cell subset. However, the transfer of splenic CD1dhiCD5+ B cells from wild type NZB/W mice into CD19−/− NZB/W recipients significantly prolonged their survival. Furthermore, regulatory T cells were significantly decreased in CD19−/− NZB/W mice, but the transfer of wild type CD1dhiCD5+ B cells induced T regulatory cell expansion in CD19−/− NZB/W mice. These results demonstrate an important protective role for regulatory B10 cells in this systemic autoimmune disease.

Protective and Pathogenic Roles for B Cells during Systemic Autoimmunity in NZB/W F1 Mice

Delineating the relative contributions of B lymphocytes during the course of autoimmune disease has been difficult. Therefore, the effects of depleting all mature B cells using a potent CD20 mAb, or of depleting circulating and marginal zone B cells using a ligand-blocking CD22 mAb, were compared in NZB/W F1 mice, a model for human systemic lupus erythematosus. Single low-dose mAb treatments depleted B cells efficiently in both NZB/W F1 and C57BL/6 mice. Prophylactic B cell depletion by repeated CD20 mAb treatments prolonged survival during pristane-accelerated lupus in NZB/W F1 mice, whereas CD22 mAb had little effect. Despite effective B cell depletion, neither mAb treatment prevented autoantibody generation. In addition, CD20, CD22, and control mAb-treated NZB/W F1 mice developed anti-mouse IgG autoantibodies in contrast to parental NZB and NZW strains, which may have reduced the effectiveness of B cell depletion. Despite this, low-dose CD20 mAb treatment initiated in 12–28-wk-old mice, and administered every 4 wk thereafter, significantly delayed spontaneous disease in NZB/W F1 mice. By contrast, B cell depletion initiated in 4-wk-old mice hastened disease onset, which paralleled depletion of the IL-10–producing regulatory B cell subset called B10 cells. B10 cells were phenotypically similar in NZB/W F1 and C57BL/6 mice, but were expanded significantly in young NZB/W F1 mice. Thus, B cell depletion had significant effects on NZB/W F1 mouse survival that were dependent on the timing of treatment initiation. Therefore, distinct B cell populations can have opposing protective and pathogenic roles during lupus progression.

CD22 Expression Mediates the Regulatory Functions of Peritoneal B-1a Cells during the Remission Phase of Contact Hypersensitivity Reactions

Although contact hypersensitivity (CHS) has been considered a prototype of T cell-mediated immune reactions, recently a significant contribution of regulatory B cell subsets in the suppression of CHS has been demonstrated. CD22, one of the sialic acid-binding immunoglobulin-like lectins, is a B cell-specific molecule that negatively regulates BCR signaling. To clarify the roles of B cells in CHS, CHS in CD22−/− mice was investigated. CD22−/− mice showed delayed recovery from CHS reactions compared with that of wild-type mice. Transfer of wild-type peritoneal B-1a cells reversed the prolonged CHS reaction seen in CD22−/− mice, and this was blocked by the simultaneous injection with IL-10 receptor Ab. Although CD22−/− peritoneal B-1a cells were capable of producing IL-10 at wild-type levels, i.p. injection of differentially labeled wild-type/CD22−/− B cells demonstrated that a smaller number of CD22−/− B cells resided in lymphoid organs 5 d after CHS elicitation, suggesting a defect in survival or retention in activated CD22−/− peritoneal B-1 cells. Thus, our study reveals a regulatory role for peritoneal B-1a cells in CHS. Two distinct regulatory B cell subsets cooperatively inhibit CHS responses. Although splenic CD1dhiCD5+ B cells have a crucial role in suppressing the acute exacerbating phase of CHS, peritoneal B-1a cells are likely to suppress the late remission phase as “regulatory B cells.” CD22 deficiency results in disturbed CHS remission by impaired retention or survival of peritoneal B-1a cells that migrate into lymphoid organs.

B-cell linker protein expression contributes to controlling allergic and autoimmune diseases by mediating IL-10 production in regulatory B cells

BACKGROUND Regulatory B cells that exhibit the cell-surface CD1d(hi)CD5(+) phenotype and produce IL-10 are termed B10 cells. Although B10 cells exert potent suppressive functions in patients with various allergic and autoimmunity disorders, the precise signaling mechanisms required for B10 cell functions remain unknown. B-cell linker protein (BLNK) is an essential component of the B-cell antigen receptor signaling pathway and is required for optimal B-cell development. OBJECTIVE We sought to elucidate the signaling pathways that are responsible for IL-10 production in B10 cells and in vivo mechanisms of how impaired B10 cell functions influence allergic and autoimmune responses. METHOD For in vitro assays, splenic CD1d(hi)CD5(+) B cells from BLNK-deficient (BLNK(-/-)) mice were analyzed for intracellular signaling pathways and cytokine production. Contact hypersensitivity (CHS) and experimental autoimmune encephalomyelitis were examined by using BLNK(-/-) mice. RESULTS Although the CD1d(hi)CD5(+) B-cell population was present in BLNK(-/-) mice, IL-10 production was impaired both in vitro and in vivo. BLNK(-/-) mice had exaggerated CHS and experimental autoimmune encephalomyelitis responses, which were normalized by adoptive transfer of splenic CD1d(hi)CD5(+) B cells from wild-type mice. In mice with CHS, BLNK(-/-) mice exhibited decreased B-cell and regulatory T-cell percentages and increased CD8(+) T-cell percentages in the skin and lymph nodes. In vitro BLNK was required for LPS-induced signal transducer and activator of transcription 3 phosphorylation in CD1d(hi)CD5(+) B cells. Finally, secreted IL-10 leads to autocrine expansion of IL-10-producing B cells. CONCLUSION BLNK serves as a critical signaling component for B10 cell function by mediating IL-10 production.

Regulatory B cells suppress imiquimod-induced, psoriasis-like skin inflammation

Psoriasis is an inflammatory cutaneous disorder characterized by marked epidermal thickening and Th1 and Th17 cell infiltration. At present, the contribution of B cells to the pathogenesis of psoriasis is unclear. In mice, topical application of imiquimod induces inflamed skin lesions and serves as an experimental animal model for human psoriasis. In this study, we showed that imiquimod‐induced skin inflammation was more severe in CD19−/− than WT mice. These inflammatory responses were negatively regulated by a unique IL‐10‐producing CD1dhiCD5+ regulatory B cell subset (B10 cells) that was absent in CD19−/− mice and represented only 1–2% of splenic B220+ cells in WT mice. Splenic B10 cells entered the circulation and migrated to draining LNs during imiquimod‐induced skin inflammation, thereby suppressing IFN‐γ and IL‐17 production. Furthermore, adoptive transfer of these B10 cells from WT mice reduced inflammation in CD19−/− mice. The present findings provide direct evidence that B10 cells regulate imiquimod‐induced skin inflammation and offer insights into regulatory B cell‐based therapies for the treatment of psoriasis.

Serum chemokine profiles in patients with alopecia areata

Background  Although chemokines play an important role in various inflammatory diseases, there have been few studies about the role of chemokines in alopecia areata (AA).

A case of milia en plaque successfully treated with oral etretinate

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Differential phosphorylation of functional tyrosines in CD19 modulates B-lymphocyte activation.

CD19 is a B‐cell transmembrane molecule that is critical for B‐cell activation. CD19 serves as a scaffold protein for key signal transduction molecules including Lyn, PI3K, and Vav, by providing docking sites for these molecules via phosphorylation of CD19‐Y513, CD19‐Y482, and CD19‐Y391. We investigated the process of CD19 tyrosine phophorylation during B‐cell activation using Ab specific for each of these phosphorylated tyrosines. BCR engagement induced differential tyrosine phosphorylation, as CD19‐Y513 phophorylation occurred first, and CD19‐Y482 phosphorylation was delayed and transient. Different BCR isotypes exhibited distinct patterns of CD19 phosphorylation: IgG‐BCR ligation resulted in faster phosphorylation of CD19‐Y513 and more intense phosphorylation of CD19‐Y391 than IgM‐BCR ligation. This affected CD19‐mediated downstream pathways involving Vav, PI3K, and Akt. Additionally, the phosphorylation profile of CD19 differed distinctly according to its plasma membrane location. CD19 phosphorylated at Y513 was almost exclusively located within lipid rafts, whereas phosphorylated Y482 and Y391 were found both inside and outside of the rafts. Furthermore, the phosphorylation of all three tyrosines was remarkably enhanced and prolonged following the simultaneous stimulation of BCR and CD40. Thus, variations in phosphorylation patterns may contribute to the complexity of CD19‐regulated signal transduction.

Intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 cooperatively contribute to the cutaneous Arthus reaction

Immune complex (IC)‐induced inflammation is mediated by inflammatory cell infiltration, a process that is highly regulated by expression of multiple adhesion molecules. The roles and interactions of ICAM‐1 and VCAM‐1, the major regulators of leukocyte firm adhesion, were examined in the cutaneous reverse‐passive Arthus reaction using ICAM‐1‐deficient (ICAM‐1−/−) mice and blocking mAb against VCAM‐1. Within 8 h, IC challenge of wild‐type mice induced edema, hemorrhage, interstitial accumulation of neutrophils and mast cells, as well as production of TNF‐α and IL‐6. All of these inflammatory parameters were reduced significantly in ICAM‐1−/− mice. The blockade of VCAM‐1 in wild‐type mice did not affect any inflammatory parameters. In contrast, ICAM‐1−/− mice treated with anti‐VCAM‐1 mAb had significantly reduced edema, hemorrhage, and neutrophil infiltration. Furthermore, VCAM‐1 blockade in ICAM‐1−/− mice suppressed cutaneous TNF‐α and IL‐6 production. Thus, VCAM‐1 plays a complementary role to ICAM‐1 in the cutaneous Arthus reaction by regulating leukocyte accumulation and proinflammatory cytokine production.

Herpetiform pemphigus without anti-desmoglein 1/3 autoantibodies

We report a patient with herpetiform pemphigus who was negative for autoantibodies to desmoglein (Dsg)1 or 3. He had erythemas with vesicles lining the margins on the trunk and extremities. Histopathology revealed intraepidermal blister with prominent eosinophil infiltration. Direct and indirect immunofluorescence demonstrated the presence of depositing and circulating immunoglobulin (Ig)G autoantibodies, but no IgA antibodies, to keratinocyte cell surface. Nonetheless, neither anti‐Dsg1 nor Dsg3 antibodies were detected by enzyme‐linked immunosorbent assay. Immunoblotting using human epidermal extracts also showed no reactivity with known intraepidermal or epidermal–dermal junctional substances. Immunoelectronmicroscopy revealed the reactivity on the portion of keratinocyte cell surface but not on the desmosomes. This case suggests that non‐desmoglein antigen on keratinocyte cell surface can be targeted in some patients with this unusual variant of pemphigus.