B lymphocytes on the front line of autoimmunity

Immune dysregulation as a leading principle for lymphoma development in diverse immunological backgrounds

Lymphoma is a heterogeneous group of malignancies arising from lymphocytes, which poses a significant challenge in terms of diagnosis and treatment due to its diverse subtypes and underlying mechanisms. This review aims to explore the shared and distinct features of various forms of lymphoma predisposing conditions, with a focus on genetic, immunological and molecular aspects. While diseases such as autoimmune disorders, inborn errors of immunity and iatrogenic immunodeficiencies are biologically and immunologically distinct, each of these diseases results in profound immune dysregulation and a predisposition to lymphoma development. Interestingly, the increased risk is often skewed towards a particular subtype of lymphoma. Patients with inborn errors of immunity in particular present with extreme forms of lymphoma predisposition, providing a unique opportunity to study the underlying mechanisms. External factors such as chronic infections and environmental exposures further modulate the risk of lymphoma development. Common features of conditions predisposing to lymphoma include: persistent inflammation, recurrent DNA damage or malfunctioning DNA repair, impaired tumor surveillance and viral clearance, and dysregulation of fundamental cellular processes such as activation, proliferation and apoptosis. Our growing understanding of the underlying mechanisms of lymphomagenesis provides opportunities for early detection, prevention and tailored treatment of lymphoma development.

Inflammatory bowel disease and immune-mediated inflammatory diseases: looking at the less frequent associations

Patients with inflammatory bowel disease (IBD) often have other immune-mediated inflammatory diseases (IMIDs), and the prevalence of any IMID is higher in IBD patients than in the general population. IBD and other IMIDs involve alterations in innate and adaptive immune responses. Their co-occurrence depends on shared immune and inflammatory processes, pathogenic mechanisms, and genetic and environmental risk factors, including drugs, especially tumor necrosis factor inhibitors. The more common IMIDs associated with IBD have been widely described, so this review focuses on the less frequent associations. The IMIDs discussed here are skin disorders (psoriasis, atopic dermatitis, vitiligo, epidermolysis bullosa acquisita, cutaneous polyarteritis nodosa, and hidradenitis suppurativa), hepato-pancreatic diseases (autoimmune hepatitis, granulomatous hepatitis, and autoimmune pancreatitis), endocrine diseases (autoimmune thyroid diseases, and type 1 diabetes mellitus), multiple sclerosis, and respiratory diseases (asthma, bronchiectasis, and interstitial pneumonia). The early detection of IMIDs in IBD patients is important to prevent their deleterious clinical course and limit their psychological impact. Care for IBD patients with IMIDs should be multispecialist, with a single therapeutic strategy instead of treating each disease separately.

c-Abl controls BCR signaling and B cell differentiation by promoting B cell metabolism

As a non-receptor tyrosine kinase, c-Abl was first studied in chronic myelogenous leukemia, and its role in lymphocytes has been well characterized. c-Abl is involved in B cell development and CD19 associated B cell antigen receptor (BCR) signaling. Although c-Abl regulates different metabolic pathways, the role of c-Abl is still unknown in B cell metabolism. In this study, B cell specific c-Abl knockout (KO) mice (Mb1^Cre+/- c-Abl^fl/fl ) were used to investigate how c-Abl regulates B cell metabolism and BCR signaling. We found that the levels of activation positive BCR signaling proximal molecules, phosphorylated spleen tyrosine kinase (pSYK) and phosphorylated Bruton tyrosine kinase (pBTK), were decreased, while the level of key negative regulator, phosphorylated SH2-containing inositol phosphatase (pSHIP1), was increased in Mb1^Cre+/- c-Abl^fl/fl mice. Furthermore, we found c-Abl deficiency weakened the B cell spreading, formation of BCR signalosomes, and the polymerization of actin during BCR activation, and also impaired the differentiation of germinal center (GC) B cells both in quiescent condition and after immunization. Moreover, B cell mitochondrial respiration and the expression of B cell metabolism regulating molecules were downregulated in c-Abl deficiency mice. Overall, c-Abl, which involved in actin remodeling and B cell metabolism, positively regulates BCR signaling and promotes GC differentiation. This article is protected by copyright. All rights reserved.

AKT2 deficiency impairs formation of the BCR signalosome

BACKGROUND

AKT2 is one of the key molecules that involves in the insulin-induced signaling and the development of cancer. In B cells, the function of AKT2 is unclear.

METHODS

In this study, we used AKT2 knockout mice model to study the role of AKT2 in BCR signaling and B cell differentiation.

RESULTS

AKT2 promotes the early activation of B cells by enhancing the BCR signaling and actin remodeling. B cells from AKT2 KO mice exhibited defective spreading and BCR clustering upon stimulation in vitro. Disruption of Btk-mediated signaling caused the impaired differentiation of germinal center B cells, and the serum levels of both sepecific IgM and IgG were decreased in the immunized AKT2 KO mice. In addition, the actin remodeling was affected due to the decreased level of the activation of WASP, the actin polymerization regulator, in AKT2 KO mice as well. As a crucial regulator of both BCR signaling and actin remodeling during early activation of B cells, the phosphorylation of CD19 was decreased in the AKT2 absent B cells, while the transcription level was normal.

CONCLUSIONS

AKT2 involves in the humoral responses, and promotes the BCR signaling and actin remodeling to enhance the activation of B cells via regulating CD19 phosphorylation. Video Abstract.

Soluble antigen arrays disarm antigen-specific B cells to promote lasting immune tolerance in experimental autoimmune encephalomyelitis

Autoreactive lymphocytes that escape central immune tolerance may be silenced via an endogenous peripheral tolerance mechanism known as anergy. Antigen-specific therapies capable of inducing anergy may restore patients with autoimmune diseases to a healthy phenotype while avoiding deleterious side effects associated with global immunosuppression. Inducing anergy in B cells may be a particularly potent intervention, as B cells can contribute to autoimmune diseases through multiple mechanisms and offer the potential for direct antigen-specific targeting through the B cell receptor (BCR). Our previous results suggested autoreactive B cells may be silenced by multivalent 'soluble antigen arrays' (SAgAs), which are polymer conjugates displaying multiple copies of autoantigen with or without a secondary peptide that blocks intracellular cell-adhesion molecule-1 (ICAM-1). Here, key therapeutic molecular properties of SAgAs were identified and linked to the immunological mechanism through comprehensive cellular and in vivo analyses. We determined non-hydrolyzable 'cSAgAs' displaying multivalent 'click'-conjugated antigen more potently suppressed experimental autoimmune encephalomyelitis (EAE) compared to hydrolyzable SAgAs capable of releasing conjugated antigen. cSAgAs restored a healthy phenotype in disease-specific antigen presenting cells (APCs) by inducing an anergic response in B cells and a subset of B cells called autoimmune-associated B cells (ABCs) that act as potent APCs in autoimmune disease. Accompanied by a cytokine response skewed towards a Th2/regulatory phenotype, this generated an environment of autoantigenic tolerance. By identifying key therapeutic molecular properties and an immunological mechanism that drives SAgA efficacy, this work guides the design of antigen-specific immunotherapies capable of inducing anergy.

IDO2 Modulates T Cell-Dependent Autoimmune Responses through a B Cell-Intrinsic Mechanism

Mechanistic insight into how adaptive immune responses are modified along the self-nonself continuum may offer more effective opportunities to treat autoimmune disease, cancer, and other sterile inflammatory disorders. Recent genetic studies in the KRN mouse model of rheumatoid arthritis demonstrate that the immunomodulatory molecule IDO2 modifies responses to self-antigens; however, the mechanisms involved are obscure. In this study, we show that IDO2 exerts a critical function in B cells to support the generation of autoimmunity. In experiments with IDO2-deficient mice, adoptive transplant experiments demonstrated that IDO2 expression in B cells was both necessary and sufficient to support robust arthritis development. IDO2 function in B cells was contingent on a cognate, Ag-specific interaction to exert its immunomodulatory effects on arthritis development. We confirmed a similar requirement in an established model of contact hypersensitivity, in which IDO2-expressing B cells are required for a robust inflammatory response. Mechanistic investigations showed that IDO2-deficient B cells lacked the ability to upregulate the costimulatory marker CD40, suggesting IDO2 acts at the T-B cell interface to modulate the potency of T cell help needed to promote autoantibody production. Overall, our findings revealed that IDO2 expression by B cells modulates autoimmune responses by supporting the cross talk between autoreactive T and B cells.

Actin-binding protein 1 links B-cell antigen receptors to negative signaling pathways

Prolonged or uncontrolled B-cell receptor (BCR) signaling is associated with autoimmunity. We previously demonstrated a role for actin in BCR signal attenuation. This study reveals that actin-binding protein 1 (Abp1/HIP-55/SH3P7) is a negative regulator of BCR signaling and links actin to negative regulatory pathways of the BCR. In both Abp1(-/-) and bone marrow chimeric mice, in which only B cells lack Abp1 expression, the number of spontaneous germinal center and marginal zone B cells and the level of autoantibody are significantly increased. Serum levels of T-independent antibody responses and total antibody are elevated, whereas T-dependent antibody responses are markedly reduced and fail to undergo affinity maturation. Upon activation, surface BCR clustering is enhanced and B-cell contraction delayed in Abp1(-/-) B cells, concurrent with slow but persistent increases in F-actin at BCR signalosomes. Furthermore, BCR signaling is enhanced in Abp1(-/-) B cells compared with wild-type B cells, including Ca(2+) flux and phosphorylation of B-cell linker protein, the mitogen-activated protein kinase kinase MEK1/2, and ERK, coinciding with reductions in recruitment of the inhibitory signaling molecules hematopoietic progenitor kinase 1 and SH2-containing inositol 5-phosphatase to BCR signalosomes. Our results indicate that Abp1 negatively regulates BCR signaling by coupling actin remodeling to B-cell contraction and activation of inhibitory signaling molecules, which contributes to the regulation of peripheral B-cell development and antibody responses.

Actin-mediated feedback loops in B-cell receptor signaling

Upon recognizing cognate antigen, B cells mobilize multiple cellular apparatuses to propagate an optimal response. Antigen binding is transduced into cytoplasmic signaling events through B-cell antigen receptor (BCR)-based signalosomes at the B-cell surface. BCR signalosomes are dynamic and transient and are subsequently endocytosed for antigen processing. The function of BCR signalosomes is one of the determining factors for the fate of B cells: clonal expansion, anergy, or apoptosis. Accumulating evidence underscores the importance of the actin cytoskeleton in B-cell activation. We have begun to appreciate the role of actin dynamics in regulating BCR-mediated tonic signaling and the formation of BCR signalosomes. Our recent studies reveal an additional function of the actin cytoskeleton in the downregulation of BCR signaling, consequently contributing to the generation and maintenance of B-cell self-tolerance. In this review, we discuss how actin remodels its organization and dynamics in close coordination with BCR signaling and how actin remodeling in turn amplifies the activation and subsequent downregulation process of BCR signaling, providing vital feedback for optimal BCR activation.

Rituximab in severe, treatment-refractory interstitial lung disease

BACKGROUND AND OBJECTIVE

In patients with severe interstitial lung disease (ILD) progressing despite conventional immunosuppression, rituximab, a B-lymphocyte depleting monoclonal antibody, may offer an effective rescue therapy.

METHODS

Retrospective assessment of 50 patients with severe, progressive ILD (of varying aetiologies, excluding idiopathic pulmonary fibrosis (IPF)) treated with rituximab between 2010 and 2012. Change in pulmonary function tests compared with pre-rituximab levels was assessed at 6-12 months post-treatment.

RESULTS

ILD was associated with connective tissue disease in 33 patients, hypersensitivity pneumonitis in 6 patients and miscellaneous conditions in 11 patients. At the time of rituximab administration, patients had severe physiologic impairment with a median forced vital capacity (FVC) of 44.0% (24.0-99.0%) and diffusing capacity of carbon monoxide (DLCO ) of 24.5% (11.4-67.0%). In contrast with a median decline in FVC of 14.3% and DLCO of 18.8% in the 6-12 months prior to rituximab, analysis of paired pulmonary function data revealed a median improvement in FVC of 6.7% (P < 0.01) and stability of DLCO (0% change; P < 0.01) in the 6-12 months following rituximab treatment. Two patients developed serious infections (pneumonia) requiring hospitalization following rituximab, and 10 patients died from progression of underlying ILD, a median of 5.1 (1.2-24.5) months after treatment.

CONCLUSIONS

In patients with severe, progressive non-IPF ILD unresponsive to conventional immunosuppression, rituximab may offer an effective therapeutic intervention. Future prospective, controlled trials are warranted to validate these findings, and to assess safety outcomes.

N-wasp is essential for the negative regulation of B cell receptor signaling

Negative regulation of receptor signaling is essential for controlling cell activation and differentiation. In B-lymphocytes, the down-regulation of B-cell antigen receptor (BCR) signaling is critical for suppressing the activation of self-reactive B cells; however, the mechanism underlying the negative regulation of signaling remains elusive. Using genetically manipulated mouse models and total internal reflection fluorescence microscopy, we demonstrate that neuronal Wiskott-Aldrich syndrome protein (N-WASP), which is coexpressed with WASP in all immune cells, is a critical negative regulator of B-cell signaling. B-cell-specific N-WASP gene deletion causes enhanced and prolonged BCR signaling and elevated levels of autoantibodies in the mouse serum. The increased signaling in N-WASP knockout B cells is concurrent with increased accumulation of F-actin at the B-cell surface, enhanced B-cell spreading on the antigen-presenting membrane, delayed B-cell contraction, inhibition in the merger of signaling active BCR microclusters into signaling inactive central clusters, and a blockage of BCR internalization. Upon BCR activation, WASP is activated first, followed by N-WASP in mouse and human primary B cells. The activation of N-WASP is suppressed by Bruton's tyrosine kinase-induced WASP activation, and is restored by the activation of SH2 domain-containing inositol 5-phosphatase that inhibits WASP activation. Our results reveal a new mechanism for the negative regulation of BCR signaling and broadly suggest an actin-mediated mechanism for signaling down-regulation.

Ro52- and Ro60-specific B cell pattern in the salivary glands of patients with primary Sjögren's syndrome

Primary Sjögren's syndrome (pSS) is characterized by the presence of autoantibodies against the ribonucleoprotein (RNP) particles Ro/SSA and La/SSB, and mononuclear cell infiltration of exocrine tissues, especially salivary and lachrymal glands. Low numbers of autoantigen-specific memory B cells and elevated levels of plasma cells have been detected previously in the peripheral blood (PB) of pSS patients compared to controls. As both Ro52 and Ro60-specific cells have been detected in the salivary glands (SG) of pSS patients, we aimed to characterize the SSA-specific B cell pattern in SG biopsies. A series of double immunohistochemical stainings were performed on paraffin-embedded tissue from 10 well-characterized pSS patients for each Ro52 and Ro60 along with CD19, CD5, CD20 or CD27, respectively. Ro52 and Ro60-specific cells detected in SG tissue were found to be CD19(+) B cells located outside the CD19(+)/CD20(+) B cell zones (BCZ) and also interstitially. These SSA-specific cells were also quantified. No SSA-specific cells were CD5(+), indicating that they do not belong to the B-1 B cell subset. Furthermore, no SSA-specific cells were observed within the CD20(+) BCZ. Hence, no SSA-specific memory B cells were detected in these individuals. Contrary to this, SSA-specific cells were found to be CD19(+)/CD27(++), demonstrating that they are differentiating short or long-lived plasma cells. Taken together, our findings suggest that these lower levels of SSA-specific memory B cells in PB and absence of SSA-specific memory B cells in SG of pSS patients could result from activation of these cells into plasma cells at the site of inflammation.

Accelerated progression of chronic lymphocytic leukemia in Eμ-TCL1 mice expressing catalytically inactive RAG1

Chronic lymphocytic leukemia (CLL) is a prevalent B-cell neoplasia that is often preceded by a more benign monoclonal CD5(+) B-cell lymphocytosis. We previously generated transgenic mice expressing catalytically inactive RAG1 (dominant-negative recombination activating gene 1 [dnRAG1] mice) that develop an early-onset indolent CD5(+) B-cell lymphocytosis attributed to a defect in secondary V(D)J rearrangements initiated to edit autoreactive B-cell receptor (BCR) specificity. Hypothesizing that CD5(+) B cells in these animals represent potential CLL precursors, we crossed dnRAG1 mice with CLL-prone Eμ-TCL1 mice to determine whether dnRAG1 expression in Eμ-TCL1 mice accelerates CLL onset. Consistent with this hypothesis, CD5(+) B-cell expansion and CLL progression occurred more rapidly in double-transgenic mice compared with Eμ-TCL1 mice. Nevertheless, CD5(+) B cells in the 2 mouse strains exhibited close similarities in phenotype, immunoglobulin gene usage, and mutation status, and expression of genes associated with immune tolerance and BCR signaling. Gene expression profiling further revealed a potential role for prolactin signaling in regulating BCR editing. These results suggest a model in which benign accumulation of CD5(+) B cells can be initiated through a failure to successfully edit autoreactive BCR specificity and may, in turn, progress to CLL upon introduction of additional genetic mutations.

Siglecs as sensors of self in innate and adaptive immune responses

Siglecs are expressed on most white blood cells of the immune system and are known to modulate the activity of cell signaling receptors via regulatory motifs in their cytoplasmic domains. This immunoglobulin subfamily of coreceptors recognize sialic acid containing glycans as ligands, which are found on glycoproteins and glycolipids of all mammalian cells. By virtue of their ability to recognize this common structural element, siglecs are increasingly recognized for their ability to help immune cells distinguish between self and nonself, and dampen autoimmune responses.

Maturation and function of human dendritic cells are regulated by B lymphocytes

Mature dendritic cells (DCs) are stimulators of T-cell immune response, whereas immature DCs support T-cell tolerance. Murine B cells can inhibit the production of IL-12 by DCs and thereby hinder the inflammatory response. Notwithstanding the importance of this modulation, only a few studies are available in humans. Here, we have developed an in vitro model of cocultures to assess its significance. We establish that human activated B cells restrained the development of monocytes into immature DCs and their differentiation into mature DCs. In addition, they decreased the density of HLA-DR from mature DCs, the expression of CD80 and CD86 coactivation molecules, the production of IL-12p70 required for antigen presentation and Th1 differentiation, and inhibited the DC-induced T-cell proliferation. These modulations were mediated by CD19(+)IgD(low)CD38(+)CD24(low)CD27(-) B cells and needed direct cell-to-cell contacts that involved CD62L for the control of CD80 and CD86 expression and a soluble factor for the control of IL-12 production. Moreover, mature DCs from patients with systemic lupus erythematosus displayed insensitivity to the regulation of IL-12. Overall, it appears that human B cells can regulate DC maturation and function and that inefficient B-cell regulation may influence an improper balance between an effector inflammatory response and tolerance induction.

Comparison of transcriptional and blood cell-phenotypic markers between operationally tolerant liver and kidney recipients

A proportion of transplant recipients can spontaneously accept their grafts in the absence of immunosuppression (operational tolerance). Previous studies identified blood transcriptional and cell-phenotypic markers characteristic of either liver or kidney tolerant recipients. However, the small number of patients analyzed and the use of different transcriptional platforms hampered data interpretation. In this study we directly compared samples from kidney and liver tolerant recipients in order to identify potential similarities in immune-related parameters. Liver and kidney tolerant recipients differed in blood expression and B-cell immunophenotypic patterns and no significant overlaps were detectable between them. Whereas some recipients coincided in specific NK-related transcripts, this observation was not reproducible in all cohorts analyzed. Our results reveal that certain immune features, but not others, are consistently present across all cohorts of operationally tolerant recipients. This provides a set of reproducible biomarkers that should be explored in future large-scale immunomonitoring trials.

Patients with drug-free long-term graft function display increased numbers of peripheral B cells with a memory and inhibitory phenotype

Several transplant patients maintain stable kidney graft function in the absence of immunosuppression. Here we compared the characteristics of their peripheral B cells to that of others who had stable graft function but were under pharmacologic immunosuppression, to patients with chronic rejection and to healthy volunteers. In drug-free long-term graft function (DF) there was a significant increase in both absolute cell number and frequency of total B cells; particularly activated, memory and early memory B cells. These increased B-cell numbers were associated with a significantly enriched transcriptional B-cell profile. Costimulatory/migratory molecules (B7-2/CD80, CD40, and CD62L) were upregulated in B cells; particularly in memory CD19(+)IgD(-)CD38(+/-)CD27(+) B cells in these patients. Their purified B cells, however, responded normally to a polyclonal stimulation and did not have cytokine polarization. This phenotype was associated with the following specific characteristics which include an inhibitory signal (decreased FcgammaRIIA/FcgammaRIIB ratio); a preventive signal of hyperactive B-cell response (an increase in BANK1, which negatively modulates CD40-mediated AKT activation); an increased number of B cells expressing CD1d and CD5; an increased BAFF-R/BAFF ratio that could explain why these patients have more peripheral B cells; and a specific autoantibody profile. Thus, our findings show that patients with DF have a particular blood B-cell phenotype that may contribute to the maintenance of long-term graft function.

Aberrant reactive oxygen and nitrogen species generation in rheumatoid arthritis (RA): causes and consequences for immune function, cell survival, and therapeutic intervention

The infiltration and persistence of hematopoietic immune cells within the rheumatoid arthritis (RA) joint results in elevated levels of pro-inflammatory cytokines, increased reactive oxygen (ROS) and -nitrogen (RNS) species generation, that feeds a continuous self-perpetuating cycle of inflammation and destruction. Meanwhile, the controlled production of ROS is required for signaling within the normal physiological reaction to perceived "foreign matter" and for effective apoptosis. This review focuses on the signaling pathways responsible for the induction of the normal immune response and the contribution of ROS to this process. Evidence for defects in the ability of immune cells in RA to regulate the generation of ROS and the consequence for their immune function and for RA progression is considered. As the hypercellularity of the rheumatoid joint and the associated persistence of hematopoietic cells within the rheumatoid joint are symptomatic of unresponsiveness to apoptotic stimuli, the role of apoptotic signaling proteins (specifically Bcl-2 family members and the tumor suppressor p53) as regulators of ROS generation and apoptosis are considered, evaluating evidence for their aberrant expression and function in RA. We postulate that ROS generation is required for effective therapeutic intervention.

Should rituximab be considered as the first-choice treatment for severe autoimmune rheumatic diseases?

The present study aimed to assess the tolerance and efficacy of rituximab (RTX), a chimeric IgG1 monoclonal antibody directed against the CD20 receptor present in B lymphocytes, in patients with autoimmune rheumatic diseases (AIRD). For this purpose, patients treated with RTX and their respective clinical charts were comprehensively examined. Indications for treatment were a refractory character of the disease, inefficacy or intolerance of other immunosuppressors. Activity indexes (SLEDAI, DAS28, and specific clinical manifestations) were used to evaluate efficacy. Serious side effects were also recorded. Seventy-four patients were included. Forty-three patients had systemic lupus erythematosus (SLE), 21 had rheumatoid arthritis (RA), 8 had Sjögren's syndrome (SS), and 2 had Takayasu's arteritis (TA). RTX was well-tolerated in 66 (89%) patients. In 8 patients (SLE=3, SS=3, RA=2), serious side effects lead to discontinuation. The mean follow-up period was 12+/-7.8 (2-35) months. The efficacy of RTX was registered in 58/66 (87%) patients, of whom 36 (83%) had SLE, 18/21 (85%) had RA, 3/8 (37%) had SS, and 1 had TA. The mean time of efficacy was 6.3+/-5.1 weeks. A significant steroid-sparing effect was noticed in half of the patients. These results add further evidence for the use of RTX in AIRD. Based on its risk-benefit ratio, RTX might be used as the first-choice treatment for patients with severe AIRD.

Th1/Th17 polarization and acquisition of an arthritogenic phenotype in arthritis-susceptible BALB/c, but not in MHC-matched, arthritis-resistant DBA/2 mice

Proteoglycan (PG) aggrecan-induced arthritis (PGIA) is a murine model of rheumatoid arthritis (RA). Although BALB/c and DBA/2 mice share the same MHC (H-2d) haplotype, the BALB/c strain is susceptible to PGIA, while DBA/2 mice are resistant. Therefore, these two inbred mouse strains provide an opportunity to study arthritis susceptibility factors excluding the effects of MHC-associated genetic components. The goal of this study was to monitor changes in the cellular composition and activation state following intra-peritoneal (i.p.) immunization to induce PGIA; additionally, we sought to identify new susceptibility factors by comparing PG-induced immune responses in BALB/c and DBA/2 mice. Upon i.p. PG injection, resident naive B1 cells are replaced by both T cells and conventional B cells in the peritoneum of BALB/c mice. These peritoneal T cells produce IFNγ and IL-17, cytokines shown to be important in RA and corresponding arthritis models. Moreover, peritoneal cells can adoptively transfer PGIA to SCID mice, demonstrating their arthritogenic properties. Our results indicate that repeatedly injected antigen leads to the recruitment and activation of immune cells in the peritoneum; these cells then trigger the effector phase of the disease. The migration and activation of T_h1/T_h17 cells in the peritoneal cavity in response to PG immunization, which did not occur in the arthritis-resistant DBA/2 strain, may be critical factors of arthritis susceptibility in BALB/c mice.

B cell characterization and reactivity analysis in multiple sclerosis

B cells are one of the key players in the pathogenesis of multiple sclerosis (MS). The peripheral B cell distributions are similar in healthy persons and MS patients. In healthy controls, B cells are rarely present in the cerebrospinal fluid (CSF) while in MS patients, a clonally expanded B cell population is detected. This consists of memory B cells, centroblasts and antibody-secreting plasma blasts and plasma cells that are responsible for intrathecal immunoglobulin G production and oligoclonal band formation in more than 90% of MS patients. Unfortunately, the targets of the autoreactive B cells and antibodies remain largely unknown. Various candidate antigens have been identified but often their involvement in the disease process is still unclear. Most studies characterizing these target antigens examined autoantibodies by analyzing sera or CSF of MS patients. An alternative approach is focusing on the clonally expanded B cells. In this way B cells directed against myelin, astroglia and axons have been denoted in MS patients. B cell immortalization, that is based on the antibody-producing potential of Epstein–Barr virus (EBV) transformed B cells, can be used to expand B cells from MS patients for the production of antibodies, that ultimately can be analysed for target identification.

Signaling pathways regulating RAG expression in B lymphocytes

Development of B-cell lymphopoiesis is dependent on the presence of recombination activating genes RAG1 and RAG2 enzymes. They control the rearrangements of immunoglobulin variable, diversity and joining region segments, and allow progression of the cellular maturation. RAG1 and RAG2 are successively up- and down-regulated at each B-cell stage to progressively generate a B-cell receptor for which unforeseeable antigenic specificity results from a stochastic process. Therefore, in autoreactive immature B cells, new round of RAG re-expression can be observed to eliminate self-reactivity. In some circumstances, RAG up-regulation can also be found in peripheral mature B lymphocytes, specifically in autoimmune diseases. It is therefore of utmost importance to unravel signaling pathways that trigger RAG induction in normal and pathological conditions. Therapeutic modulation of cytokines or intracellular contacts involved in RAG expression might restrict the development of inappropriate autoimmune repertoire.

Pulmonary eosinophilia

Eosinophils may infiltrate the lung tissue, thus impairing gas exchange and causing several symptoms as dyspnea, fever, and cough. This process may be secondary to several factors, including drugs or parasite migration, or primary (idiopathic). Acute eosinophilic pneumonia is life-threatening and presents frequently in young smokers as an acute hypoxemic respiratory failure of generally less than a week with bilateral lung infiltrates, frequently misdiagnosed as severe community-acquired pneumonia. This patients present without peripheral eosinophilia but usually have more than 25% eosinophils on bronchoalveolar fluid. Chronic eosinophilic pneumonia is a protracted disease of usually more than a month before presentation, with a predilection for middle aged asthmatic patients. Hypoxemia is mild-moderate, and there are usually more than 1,000 eosinophils/mm3 of peripheral blood. Bronchoalveolar fluid has high eosinophil levels (usually more than 25%). Migratory peripheral infiltrates are seen in the chest x-ray film. Both acute and chronic eosinophilic pneumonia are treated by glucocorticoids and respiratory support as well as avoidance of any recognized trigger.

Towards understanding the pathology of erythema nodosum leprosum

Erythema nodosum leprosum (ENL) is an immune-mediated complication of leprosy presenting with inflammatory skin nodules and involvement of multiple organ systems, often running a protracted course. Immune complex production and deposition as well as complement activation have long been regarded as the principal aetiology of ENL. However, new data show that cell-mediated immunity is also important. We have performed a critical analysis of studies on the pathology of ENL. Our main findings are as follows. ENL is characterised by an inflammatory infiltrate of neutrophils with vasculitis and/or panniculitis. There is deposition of immune complexes and complement together with Mycobacterium leprae antigens in the skin. Changes in serum levels of Igs indicate a transient, localised immune response. The major T-cell subtype in ENL is the CD4 cell, in contrast to lepromatous leprosy where CD8 cells predominate. The cytokines TNFalpha and IL-6 are consistently found whilst IL-4 is low or absent in ENL lesions, indicating a T(H)1 type response. Keratinocyte 1a and intercellular adhesion molecule-1 (ICAM-1) have been shown to be present in the epidermis in ENL, which is evidence of a cell-mediated immune response. Co-stimulatory molecules such as B7-1 have also been studied but further work is needed to draw strong conclusions. We also highlight potential areas for future research.

Act1 modulates autoimmunity through its dual functions in CD40L/BAFF and IL-17 signaling

Coordinated regulation of T and B cell-mediated immune responses plays a critical role in the control and modulation of autoimmune diseases. This review is focused on the adapter molecule Act1 and its regulation of autoimmunity through its impact on both T and B cell-mediated immune responses. Whereas Act1 molecule is an important negative regulator for B cell-mediated humoral immune responses through its function in CD40L and BAFF signaling, recent studies have shown that Act1 is also a key positive signaling component for IL-17 signaling pathway, critical for T(H)17-mediated autoimmune and inflammatory responses. The dual functions of Act1 are evident in Act1-deficient mice that displayed B cell-mediated autoimmune phenotypes (including dramatic increase in peripheral B cells, lymphadenopathy and splenomegaly, hypergammaglobulinemia and Sjogren's disease in association with Lupus Nephritis), but showed resistance to T(H)17-dependent EAE and colitis. Such seemingly opposite functions of Act1 in CD40-BAFFR and IL-17R signaling are orchestrated by different domains in Act1. Whereas Act1 interacts with the IL-17R through the C-terminal SEFIR domain, Act1 is recruited to CD40 and BAFFR indirectly, which is mediated by TRAF3 through the TRAF binding site in Act1. Such delicate regulatory mechanisms may provide a common vehicle to promote balance between host defense to pathogens and tolerance to self.

B-cell lymphoproliferation in chronic inflammatory rheumatic diseases

Patients with chronic inflammatory rheumatic diseases, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and especially primary Sjögren's syndrome (SS), are at higher risk than the general population of developing B-cell non-Hodgkin lymphoma (NHL). Analyses of the association between various lymphoma subtypes and specific disease entities suggest that this association might be mediated by disease-specific mechanisms, as well as by mechanisms unique to lymphoma subtype. These specific associations can provide important information about abnormal B-cell stimulation in these conditions. Patients with primary SS, SLE and RA are at high risk of developing diffuse large B-cell lymphomas, a group of high-grade NHLs with remarkable heterogeneity. Patients with primary SS are at particularly high risk of developing marginal-zone B-cell lymphomas. The risk factors of lymphoma development in primary SS seem to be closely related to the underlying mechanisms of abnormal stimulation and/or impaired censoring mechanisms of B cells. In patients with RA and SLE, more intense disease activity and/or long-lasting disease might be indications of a higher risk of lymphoma development. This Review will focus on the risk of lymphoma, common and disease-specific mechanisms of B-cell lymphoma development, and on the clinical consequences of lymphoma in patients with inflammatory rheumatic diseases.

Abrogation of nephrotic proteinuria by rituximab treatment in a renal transplant patient with relapsed focal segmental glomerulosclerosis

Relapse of focal segmental glomerulosclerosis (FSGS) after renal transplantation is 20-40%. Recurrence after a first relapse is 80%. The only current treatment is plasmapheresis and/or cyclophosphamide. We report successful treatment of a second relapse in a 48-year-old patient. At age 33, FSGS was diagnosed. The patient began hemodialysis 1 year later. In her first renal transplant, she developed recurrent FSGS and reached terminal transplant failure 3 years later. Eight years later, a second transplant was performed. Immunosuppressive regimen: steroids, mycophenolate mofetil (MMF), tacrolimus (TAC), and rabbit anti-thymocyte globulin. Proteinuria of 2-6 g/day was detected and a biopsy showed recurrent FSGS. Plasmapheresis was started without success. Another biopsy still showed FSGS. The patient received two doses of rituximab (375 mg/m2 each) i.v. Three weeks later, proteinuria was 350 mg/day (serum-creatinine 1.6 mg/dl). Twelve months later, proteinuria was at 90 mg/day. Rituximab might be an option for recurrent FSGS after renal transplantation.

Possible therapeutic applications of single-chain antibodies in systemic autoimmune diseases

B cells participate in the induction and maintenance of systemic autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus, via production of pathogenic autoantibodies, contributing to the formation of immune complexes. Immune complex deposition in the kidney and joints causes inflammation and organ destruction, and chemokine production enhances T cell activation and tissue damage. The development of the disorder depends on several factors, for example, genetic susceptibility, environmental factors or immune dysregulation. Traditional therapies, which aimed at the alleviation of symptoms, are giving way to biological therapies with the potential of disrupting disease progression. This article focuses on antibody therapies, especially on the applications of single-chain antibodies, as new biological agents for the treatment of systemic autoimmune disorders.

Immune-mediated inflammatory diseases (IMIDs) and biologic therapy: a medical revolution

Targeted biologic therapies have revolutionised treatment of immune-mediated inflammatory diseases (IMIDs) due to their efficacy, speed of onset and tolerability. The discovery that clinically unrelated conditions, such as rheumatoid arthritis and Crohn's disease, share similar immune dysregulation has led to a shift in the management of IMIDs from one of organ-based symptom relief to mechanism-based treatment. The fact that anticytokine therapy has been effective in treating multiple orphan inflammatory conditions confirms the IMID paradigm. In this review we examine the biologic agents currently licensed for use in the US and Europe: infliximab, etanercept, adalimumab, rituximab, abatacept, anakinra, alefacept and efalizumab. We also discuss the rationale behind the management of IMIDs using rheumatoid arthritis, Crohn's disease, psoriasis and psoriatic arthritis as examples. For the medical profession, IMID represents a breakthrough in the way pathology is classified. In this burgeoning era of biologic therapy the prospect of complete disease remission is conceivable.