Impaired LAIR-1-mediated immune control due to collagen degradation in fibrosis

Tissue repair is disturbed in fibrotic diseases like systemic sclerosis (SSc), where the deposition of large amounts of extracellular matrix components such as collagen interferes with organ function. LAIR-1 is an inhibitory collagen receptor highly expressed on tissue immune cells. We questioned whether in SSc, impaired LAIR-1-collagen interaction is contributing to the ongoing inflammation and fibrosis. We found that SSc patients do not have an intrinsic defect in LAIR-1 expression or function. Instead, fibroblasts from healthy controls and SSc patients stimulated by soluble factors that drive inflammation and fibrosis in SSc deposit disorganized collagen products in vitro, which are dysfunctional LAIR-1 ligands. This is dependent of matrix metalloproteinases and platelet-derived growth factor receptor signaling. In support of a non-redundant role of LAIR-1 in the control of fibrosis, we found that LAIR-1-deficient mice have increased skin fibrosis in response to repeated injury and in the bleomycin mouse model for SSc. Thus, LAIR-1 represents an essential control mechanism for tissue repair. In fibrotic disease, excessive collagen degradation may lead to a disturbed feedback loop. The presence of functional LAIR-1 in patients provides a therapeutic opportunity to reactivate this intrinsic negative feedback mechanism in fibrotic diseases.

Epicutaneous Staphylococcus aureus induces IL-36 to enhance IgE production and ensuing allergic disease

IgE induced by type 2 immune responses in atopic dermatitis is implicated in the progression of atopic dermatitis to other allergic diseases, including food allergies, allergic rhinitis, and asthma. However, the keratinocyte-derived signals that promote IgE and ensuing allergic diseases remain unclear. Herein, in a mouse model of atopic dermatitis-like skin inflammation induced by epicutaneous Staphylococcus aureus exposure, keratinocyte release of IL‑36α along with IL-4 triggered B cell IgE class-switching, plasma cell differentiation, and increased serum IgE levels-all of which were abrogated in IL-36R-deficient mice or anti-IL‑36R-blocking antibody-treated mice. Moreover, skin allergen sensitization during S. aureus epicutaneous exposure-induced IL-36 responses was required for the development of allergen-specific lung inflammation. In translating these findings, elevated IL‑36 cytokines in human atopic dermatitis skin and in IL‑36 receptor antagonist-deficiency patients coincided with increased serum IgE levels. Collectively, keratinocyte-initiated IL‑36 responses represent a key mechanism and potential therapeutic target against allergic diseases.

IL36 is a critical upstream amplifier of neutrophilic lung inflammation in mice

IL-36, which belongs to the IL-1 superfamily, is increasingly linked to neutrophilic inflammation. Here, we combined in vivo and in vitro approaches using primary mouse and human cells, as well as, acute and chronic mouse models of lung inflammation to provide mechanistic insight into the intercellular signaling pathways and mechanisms through which IL-36 promotes lung inflammation. IL-36 receptor deficient mice exposed to cigarette smoke or cigarette smoke and H1N1 influenza virus had attenuated lung inflammation compared with wild-type controls. We identified neutrophils as a source of IL-36 and show that IL-36 is a key upstream amplifier of lung inflammation by promoting activation of neutrophils, macrophages and fibroblasts through cooperation with GM-CSF and the viral mimic poly(I:C). Our data implicate IL-36, independent of other IL-1 family members, as a key upstream amplifier of neutrophilic lung inflammation, providing a rationale for targeting IL-36 to improve treatment of a variety of neutrophilic lung diseases.

BTK inhibition modulates multiple immune cell populations involved in the pathogenesis of immune mediated nephritis

Lupus nephritis (LN) is a serious end organ complication of systemic lupus erythematosus. Nephrotoxic serum nephritis (NTN) is an inducible model of LN, which utilizes passive transfer of pre-formed nephrotoxic antibodies to initiate disease. In previous studies, we demonstrated that the Bruton's tyrosine kinase inhibitor, BI-BTK-1, prevents the development of nephritis in NTN when treatment was started prior to nephrotoxic serum transfer, and reverses established proteinuria as well. We manipulated the initiation and duration of BI-BTK-1 therapy in NTN to study its delayed therapeutic effects when treatment is given later in the disease course, as well as to further understand what effect BI-BTK-1 is having to prevent initiation of nephritis with early treatment. Early treatment and remission induction each correlated with decreased inflammatory macrophages, CD4+ and CD8+ T cells, and decreased B220+ B cells. Additionally, an increased proportion of resident macrophages within the CD45+ population favored a delay of disease onset and remission induction. We also studied the cellular processes involved in reactivation of nephritis by withdrawing BI-BTK-1 treatment at different time points. Treatment cessation led to either early or later onset of renal flares inversely dependent on the initial duration of BTK inhibition, as assessed by increased proteinuria and BUN levels and worse renal pathology. These flares were associated with an increase in kidney CD45+ infiltrates, including myeloid cell populations. IL-6, CD14, and CCL2 were also increased in mice developing late flares. These analyses point to the role of macrophages as an important contributor to the pathogenesis of immune mediated nephritis, and further support the therapeutic potential of BTK inhibition in this disease and related conditions.

Transcriptional insights into pathogenesis of cutaneous systemic sclerosis using pathway driven meta-analysis assisted by machine learning methods

Pathophysiology of systemic sclerosis (SSc, Scleroderma), an autoimmune rheumatic disease, comprises of mechanisms that drive vasculopathy, inflammation and fibrosis. Understanding of the disease and associated clinical heterogeneity has advanced considerably in the past decade, highlighting the necessity of more specific targeted therapy. While many of the recent trials in SSc failed to meet the primary end points that predominantly relied on changes in modified Rodnan skin scores (MRSS), sub-group analysis, especially those focused on the basal skin transcriptomic data have provided insights into patient subsets that respond to therapies. These findings suggest that deeper understanding of the molecular changes in pathways is very important to define disease drivers in various patient subgroups. In view of these challenges, we performed meta-analysis on 9 public available SSc microarray studies using a novel pathway pivoted approach combining consensus clustering and machine learning assisted feature selection. Selected pathway modules were further explored through cluster specific topological network analysis in search of novel therapeutic concepts. In addition, we went beyond previously described SSc class divisions of 3 clusters (e.g. inflammation, fibro-proliferative, normal-like) and expanded into a much finer stratification in order to profile SSc patients more accurately. Our analysis unveiled an important 80 pathway signatures that differentiated SSc patients into 8 unique subtypes. The 5 pathway modules derived from such signature successfully defined the 8 SSc subsets and were validated by in-silico cellular deconvolution analysis. Myeloid cells and fibroblasts involvement in different clusters were confirmed and linked to corresponding pathway activities. Collectively, our findings revealed more complex disease subtypes in SSc; Key gene mediators such as IL6, FGFR1, TLR7, PLCG2, IRK2 identified by network analysis underscored the scientific rationale for exploring additional targets in treatment of SSc.

Safety, pharmacokinetics and pharmacodynamics of BI 705564, a highly selective, covalent inhibitor of Bruton's tyrosine kinase, in Phase I clinical trials in healthy volunteers

Aims

To evaluate the safety, pharmacokinetics and pharmacodynamics of single‐ and multiple‐rising doses (MRDs) of BI 705564 and establish proof of mechanism.

Methods

BI 705564 was studied in 2 placebo‐controlled, Phase I clinical trials testing single‐rising doses (1–160 mg) and MRDs (1–80 mg) of BI 705564 over 14 days in healthy male volunteers. Blood samples were analysed for BI 705564 plasma concentration, Bruton's tyrosine kinase (BTK) target occupancy (TO) and CD69 expression in B cells stimulated ex vivo. A substudy was conducted in allergic, otherwise healthy, MRD participants. Safety was assessed in both studies.

Results

All doses of BI 705564 were well tolerated. Geometric mean BI 705564 plasma terminal half‐life ranged from 10.1 to 16.9 hours across tested doses, with no relevant accumulation after multiple dosing. Doses ≥20 mg resulted in ≥85% average TO that was maintained for ≥48 hours after single‐dose administration. Functional effects of BTK signalling were demonstrated by dose‐dependent inhibition of CD69 expression. In allergic participants, BI 705564 treatment showed a trend in wheal size reduction in a skin prick test and complete inhibition of basophil activation. Mild bleeding‐related adverse events were observed with BI 705564; bleeding time increased in 1/12 participants (8.3%) who received placebo vs 26/48 (54.2%) treated with BI 705564.

Conclusion

BI 705564 showed efficient target engagement through durable TO and inhibition of ex vivo B‐cell activation, and proof of mechanism through effects on allergic skin responses. Mild bleeding‐related adverse events were probably related to inhibition of platelet aggregation by BTK inhibition.

Phoenix from the flames: Rediscovering the role of the CD40-CD40L pathway in systemic lupus erythematosus and lupus nephritis

Lupus nephritis (LN) is a significant complication of systemic lupus erythematosus (SLE), increasing its morbidity and mortality. Although the current standard of care helps suppress disease activity, it is associated with toxicity and ultimately does not cure SLE. At present, there are no therapies specifically indicated for the treatment of LN and there is an unmet need in this disease where treatment remains a challenge. The CD40-CD40L pathway is central to SLE pathogenesis and the generation of autoantibodies and their deposition in the kidneys, resulting in renal injury in patients with LN. CD40 is expressed on immune cells (including B cells, monocytes and dendritic cells) and also non-haematopoietic cells. Interactions between CD40L on T cells and CD40 on B cells in the renal interstitium are critical for the local expansion of naive B cells and autoantibody-producing B cells in LN. CD40L-mediated activation of myeloid cells and resident kidney cells, including endothelial cells, proximal tubular epithelial cells, podocytes and mesangial cells, further amplifies the inflammatory milieu in the interstitium and the glomeruli. Several studies have highlighted the upregulated expression of CD40 in LN kidney biopsies, and preclinical data have demonstrated the importance of the CD40-CD40L pathway in murine SLE and LN. Blocking this pathway is expected to ameliorate inflammation driven by infiltrating immune cells and resident kidney cells. Initial experimental therapeutic interventions targeting the CD40-CD40L pathway, based on CD40L antibodies, were associated with an increased incidence of thrombosis. However, this safety issue has not been observed with second-generation CD40/CD40L antibodies that have been engineered to prevent platelet activation. With these advancements, together with recent preclinical and clinical findings, it is anticipated that selective blockade of the CD40-CD40L pathway may address the unmet treatment needs in SLE, LN and other autoimmune diseases.

Gut T cell-independent IgA responses to commensal bacteria require engagement of the TACI receptor on B cells

The gut mounts secretory immunoglobulin A (SIgA) responses to commensal bacteria through nonredundant T cell-dependent (TD) and T cell-independent (TI) pathways that promote the establishment of mutualistic host-microbiota interactions. SIgAs from the TD pathway target penetrant bacteria, and their induction requires engagement of CD40 on B cells by CD40 ligand on T follicular helper cells. In contrast, SIgAs from the TI pathway bind a larger spectrum of bacteria, but the mechanism underpinning their production remains elusive. Here, we show that the intestinal TI pathway required CD40-independent B cell-activating signals from TACI, a receptor for the innate CD40 ligand-like factors BAFF and APRIL. TACI-induced SIgA responses targeted a fraction of the gut microbiota without shaping its overall composition. Of note, TACI was dispensable for TD induction of IgA in gut-associated lymphoid organs. Thus, BAFF/APRIL signals acting on TACI orchestrate commensal bacteria-specific SIgA responses through an intestinal TI program.

Effects of BI 655064, an antagonistic anti-CD40 antibody, on clinical and biomarker variables in patients with active rheumatoid arthritis: a randomised, double-blind, placebo-controlled, phase IIa study

OBJECTIVE

To evaluate the safety, efficacy and therapeutic mechanism of BI 655064, an antagonistic anti-CD40 monoclonal antibody, in patients with rheumatoid arthritis (RA) and an inadequate response to methotrexate (MTX-IR).

METHODS

In total, 67 patients were randomised to receive weekly subcutaneous doses of 120 mg BI 655064 (n=44) or placebo (n=23) for 12 weeks. The primary endpoint was the proportion of patients who achieved 20% improvement in American College of Rheumatology criteria (ACR20) at week 12. Safety was assessed in patients who received at least one dose of study drug.

RESULTS

At week 12, the primary endpoint was not met, with 68.2% of patients treated with BI 655064 achieving an ACR20 vs 45.5% with placebo (p=0.064); using Bayesian analysis, the posterior probability of seeing a difference greater than 35% was 42.9%. BI 655064 was associated with greater changes in CD40-CD40L pathway-related markers, including reductions in inflammatory and bone resorption markers (interleukin-6, matrix metalloproteinase-3, receptor activator of nuclear factor-κB ligand), concentration of autoantibodies (immunoglobulin [Ig]G rheumatoid factor [RF], IgM RF, IgA RF) and CD95+ activated B-cell subsets. No serious adverse events (AEs) related to BI 655064 treatment or thromboembolic events occurred; reported AEs were mainly of mild intensity.

CONCLUSION

Although blockade of the CD40-CD40L pathway with BI 655064 in MTX-IR patients with RA resulted in marked changes in clinical and biological parameters, including reductions in activated B-cells, autoantibody production and inflammatory and bone resorption markers, with a favourable safety profile, clinical efficacy was not demonstrated in this small phase IIa study.

TRIAL REGISTRATION NUMBER

NCT01751776.

BTK inhibition ameliorates kidney disease in spontaneous lupus nephritis

Lupus nephritis is a common disease manifestation of SLE, in which immune complex deposition and macrophage activation are important contributors to disease pathogenesis. Bruton's tyrosine kinase (BTK) plays an important role in both B cell and FcgammaR mediated myeloid cell activation. In the current study, we examined the efficacy of BI-BTK-1, a recently described irreversible BTK inhibitor, in the classical NZB × NZW F1 (NZB/W) and MRL/lpr spontaneous mouse models of SLE. NZB/W mice were randomly assigned to a treatment (0.3 mg/kg, 1 mg/kg, 3 mg/kg and 10 mg/kg) or control group and began treatment at 22 weeks of age. The experimental setup was similar in MRL/lpr mice, but with a single treated (10 mg/kg, beginning at 8-9 weeks of age) and control group. A separate experiment was performed in the MRL/lpr strain to assess the ability of BI-BTK-1 to reverse established kidney disease. Early treatment with BI-BTK-1 significantly protected NZB/W and MRL/lpr mice from the development of proteinuria, correlating with significant renal histological protection, decreased anti-DNA titers, and increased survival in both strains. BI-BTK-1 treated mice displayed a significant decrease in nephritis-associated inflammatory mediators (e.g. LCN2 and IL-6) in the kidney, combined with a significant inhibition of immune cell infiltration and accumulation. Importantly, BI-BTK-1 treatment resulted in the reversal of established kidney disease. BTK inhibition significantly reduced total B cell numbers and all B cell subsets (immature, transitional, follicular, marginal zone, and class switched) in the spleen of NZB/W mice. Overall, the significant efficacy of BI-BTK-1 in ameliorating multiple pathological endpoints associated with kidney disease in two distinct murine models of spontaneous lupus nephritis provides a strong rationale for BTK inhibition as a promising treatment approach for lupus nephritis.

BTK inhibition ameliorates renal, skin, and brain disease in a spontaneous murine model of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) can affect multiple different organ systems, including the kidneys (lupus nephritis, LN), brain (neuropsychiatric SLE, NPSLE), and skin (cutaneous lupus, CLE). B cells and macrophages are implicated in the pathogenesis of these disease manifestations. We have previously shown the importance of Bruton’s tyrosine kinase (BTK), an enzyme important in B cell and macrophage signaling, in reversing disease in a model of immune nephritis induced by the passive transfer of nephrotoxic antibodies.

To extend our findings to a more severe type of nephritis more similar to human disease and examine the effects of BTK inhibition on extra-renal lupus manifestations, we treated a spontaneous model of lupus, MRL/lpr mice, with the novel BTK inhibitor, BI-BTK-1. Early treatment with BI-BTK-1 normalized proteinuria (p<0.001) and BUN (p<0.001) levels, and significantly improved renal histopathology. Importantly, in separate studies BTK inhibition also significantly reversed established proteinuria. Finally, BI-BTK-1 treated MRL/lpr mice had significantly improved survival as compared to control treated age, sex, and background matched mice (p < 0.0001).

MRL/lpr mice develop brain and skin disease that model the pathology of NPSLE and CLE, respectively. Early BI-BTK-1 treatment significantly improved cognitive function and decreased inflammatory cell infiltration into the brain choroid plexus. Moreover, skin disease was also significantly improved as determined by attenuated macroscopic and histologic skin scores.

Our results further highlight the therapeutic potential of BI-BTK-1 in SLE, not only in treatment of LN, but potentially also for skin and brain disease as well.

Highly selective inhibition of Bruton's tyrosine kinase attenuates skin and brain disease in murine lupus

Background

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that affects different end organs, including skin and brain. We and others have previously shown the importance of macrophages in the pathogenesis of cutaneous and neuropsychiatric lupus. Additionally, autoantibodies produced by autoreactive B cells are thought to play a role in both the skin and central nervous system pathologies associated with SLE.

Methods

We used a novel inhibitor of Bruton’s tyrosine kinase (BTK), BI-BTK-1, to target both macrophage and B cell function in the MRL-lpr/lpr murine model of SLE, and examined the effect of treatment on skin and brain disease.

Results

We found that treatment with BI-BTK-1 significantly attenuated the lupus associated cutaneous and neuropsychiatric disease phenotypes in MRL/lpr mice. Specifically, BI-BTK-1 treated mice had fewer macroscopic and microscopic skin lesions, reduced cutaneous cellular infiltration, and diminished inflammatory cytokine expression compared to control mice. BTK inhibition also significantly improved cognitive function, and decreased accumulation of T cells, B cells, and macrophages within the central nervous system, specifically the choroid plexus.

Conclusions

Directed therapies may improve the response rate in lupus-driven target organ involvement, and decrease the dangerous side effects associated with global immunosuppression. Overall, our results suggest that inhibition of BTK may be a promising therapeutic option for cutaneous and neuropsychiatric disease associated with SLE.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1500-0) contains supplementary material, which is available to authorized users.

Human Secretory IgM Emerges from Plasma Cells Clonally Related to Gut Memory B Cells and Targets Highly Diverse Commensals

Secretory immunoglobulin A (SIgA) enhances host-microbiota symbiosis, whereas SIgM remains poorly understood. We found that gut IgM⁺ plasma cells (PCs) were more abundant in humans than mice and clonally related to a large repertoire of memory IgM⁺ B cells disseminated throughout the intestine but rare in systemic lymphoid organs. In addition to sharing a gut-specific gene signature with memory IgA⁺ B cells, memory IgM⁺ B cells were related to some IgA⁺ clonotypes and switched to IgA in response to T cell-independent or T cell-dependent signals. These signals induced abundant IgM which, together with SIgM from clonally affiliated PCs, recognized mucus-embedded commensals. Bacteria recognized by human SIgM were dually coated by SIgA and showed increased richness and diversity compared to IgA-only-coated or uncoated bacteria. Thus, SIgM may emerge from pre-existing memory rather than newly activated naive IgM⁺ B cells and could help SIgA to anchor highly diverse commensal communities to mucus.

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IgM⁺ PCs generating SIgM are relatively abundant in human but not mouse gut

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IgM⁺ PCs clonally relate to a large gut repertoire of memory IgM⁺ B cells

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Gut memory IgM⁺ B cells express a tissue-specific signature and can switch to IgA

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Human but not mouse SIgM binds a highly diverse microbiota dually coated by SIgA

Remission induction of established nephritis by therapeutic administration of a novel BTK inhibitor in an inducible model of lupus nephritis

Lupus nephritis (LN) patients currently lack highly effective and safe treatment options. Bruton’s tyrosine kinase (BTK) is a tyrosine kinase which is important for B cell and macrophage function. Based on preliminary studies in an inducible model of nephritis that highlighted the importance of BTK dependent macrophage effector function in the pathogenesis of disease, we extended our studies to explore the effect of BTK inhibition on remission induction of established, proliferative nephritis.

Nephritis was induced in female 129 sv/J mice (10 weeks of age) via the passive transfer of nephrotoxic serum (NTS). Once a mouse developed severe nephritis (>300 mg/dl proteinuria for two consecutive days, or a single measurement of >2000 mg/dl), treatment begun via daily oral gavage with 3 mg/kg of BI-BTK-1, a novel, highly selective and potent BTK inhibitor. Each treated mouse was matched to a control mouse that received daily gavage of the vehicle alone.

Within two days of beginning treatment, mice treated with BI-BTK-1 had a significant reversal of the proteinuria compared to vehicle control treated mice (p<0.05). Terminal urine revealed a significantly reduced A:C ratios (p <0.001). Additionally, terminal serum revealed normalized BUN levels. Histological assessment revealed significant structural protection in the treated compared to control treated mice, including both glomerular (p<0.001) and tubular compartments (p < 0.001). Kidney RT-PCR and RNA-seq analysis are currently in progress.

Therapeutic treatment with BI-BTK-1 reversed severe, established nephritis induced by pathogenic antibodies. These exciting results indicate the novel therapeutic potential of BTK inhibition for treating LN patients with established disease.

Identification and characterization of an antagonistic anti-mouse CD40 antibody

Targeting CD40-CD40L interactions has been an interesting drug concept for the treatment of autoimmune diseases given this pathway’s role in the development of both humoral and cell mediated immune responses. While preclinical blockade of CD40L is well documented in various autoimmune animal models of disease, limited data exists for CD40 blockade due to lack of a truly antagonistic anti-mouse CD40 tool antibody (Ab). Here we describe the in vitro and in vivo characterization of a fully antagonistic anti-mouse CD40 monoclonal Ab (BI CD40-1); a chimeric rat Fv anti-mouse CD40 mAb engineered with a mouse IgG2a Fc containing mutations to abrogate Fcγ receptor binding. BI CD40-1 blocks molecular CD40-CD40L interactions (IC50 = 0.25 nM) and exhibits potent binding to CD40 expressed on mouse B cells (EC50 = 0.42 nM ± 0.08). In vitro profiling of BI CD40-1 using a mouse splenocyte proliferation assay confirmed potent antagonistic activity (IC50 = 0.27 nM ± 0.09) as well as absence of any agonistic properties (stimulation index < 2 @ 67 nM). Administration of BI CD40-1 to mice prior to ovalbumin (OVA) immunization resulted in dose-dependent blockade of OVA-specific IgG responses (100, 100, 74, 0% inhibition at 10, 3, 1, and 0.3 MPK; day 13) correlating with similar dose dependent receptor occupancy and inhibition of B cell activation as measured by ex vivo CD54 upregulation. Prophylactic dosing in cGVHD model of scleroderma showed dose dependent protection in disease development as seen by decreased dermal thickness, myofibroblast counts and collagen deposition. BI CD40-1 represents a novel fully antagonistic anti-mouse CD40 mAb, an important tool for mechanistic understanding of the therapeutic value of targeting of CD40 in inflammatory diseases.

A novel anti-CD40 antibody prevents activation of alloreactive T cells and prolongs skin allograft survival

Targeting the CD40-CD154 pathway to induce transplantation tolerance has been of interest to transplantation immunologists for over two decades. The efficacy of anti-CD154 antibody (Ab) observed in murine and non-human primate models for preventing allograft rejection and suppressing autoimmunity, generated great interest in the development of this antibody for clinical use. However, clinical trials with anti-CD154 Ab resulted in thromboembolic complications in patients as a result of CD154 expression by human platelets and limited the clinical application. To develop an alternative approach to anti-CD154 Ab, recent efforts have focused on targeting its receptor, CD40. In this study we evaluated the effects of a novel murine antagonistic antibody to CD40 (BI CD40-1) on alloreactive immune responses. Costimulation blockade consisting of donor splenocytes (DST) and BI CD40-1 reduced activation of alloreactive CD8 T cells as shown by inhibition of expansion, decreased cytokine production and decreased killing of allogeneic targets using an in vivo cytotoxicity assay. Moreover DST/BI CD40-1 treatment significantly prolonged skin graft survival in a BALB/c to B6 MHC mismatch model. The efficacy of BI CD40-1 in preventing alloreactive T cell responses was similar to anti-CD154 Ab. These results indicate that anti-CD40 Ab is an attractive candidate for translation to clinical application.

Therapeutic blockade of immune complex-mediated glomerulonephritis by highly selective inhibition of Bruton’s tyrosine kinase

Lupus nephritis (LN) is a potentially dangerous end organ pathology that affects upwards of 60% of SLE patients. Bruton’s tyrosine kinase (BTK) is important for B cell development, Fc receptor signaling, and macrophage polarization. In this study, we investigated the effects of a novel, highly selective and potent BTK inhibitor, BI-BTK-1, in an inducible model of LN in which mice receive nephrotoxic serum (NTS) containing anti-glomerular antibodies. Mice were treated once daily with vehicle alone or BI-BTK-1 (0.3–10 mg/kg, n=16/group), either prophylactically or therapeutically.

When compared with control treated mice, NTS-challenged mice treated prophylactically with BI-BTK-1 exhibited significantly attenuated disease which was dose dependent, as measured by proteinuria, serum creatinine, and serum BUN. Histological assessment confirmed marked renal protection in the BI-BTK-1 treatment groups. BI-BTK-1 treatment resulted in decreased recruitment of inflammatory monocytes from the splenic reservoir, and a decrease in infiltrating IBA-1+ cells, as well as C3 deposition, within the kidney. RT-PCR on whole kidney RNA and serum profiling indicated that BTK inhibition significantly decreased levels of LN-relevant inflammatory cytokines and chemokines. Renal RNA expression profiling by RNA-seq revealed that BI-BTK-1 dramatically modulated pathways related to inflammation and glomerular injury. Importantly, when administered therapeutically, BI-BTK-1 reversed established proteinuria and improved renal histopathology.

Our results highlight the important role for BTK in the pathogenesis of immune complex-mediated nephritis, and BTK inhibition as a promising therapeutic target for LN.

Therapeutic targeting of macrophages in lupus nephritis

Systemic lupus erythematosus (SLE) is an autoimmune disease which results in multiple different end organ pathologies, including the kidney. Lupus nephritis (LN) is one of the most serious complications of SLE, and a leading cause of morbidity and mortality. Current treatment options are suboptimal, involving non-specific immunosuppression which exposes patients to potentially serious side effects with no guarantee of remission. More targeted therapeutic approaches may improve treatment results. Many studies have implicated macrophages as actively contributing to LN pathogenesis in both human and murine disease. Indeed, various studies have shown that depletion of macrophage populations, inhibition of macrophage recruitment, and disruption of inflammatory macrophage activation and polarization have significantly ameliorated nephritis in several different murine LN models. The current literature explores targeting macrophages by several different means, including the CSF-1/CSF-1R signaling axis, the CX3CL1/CX3CR1 signaling axis, the CCL2/CCR2 signaling axis, and Bruton's Tyrosine Kinase (BTK), all of which hold promise as targets for future LN treatments. These studies highlight the potential benefit of targeting macrophages in LN, and emphasize the need for future investigations to discern the ideal mean(s) for targeting macrophages in LN.

Suppression of glomerulonephritis in lupus-prone NZB × NZW mice by RN486, a selective inhibitor of Bruton's tyrosine kinase

OBJECTIVE

Bruton's tyrosine kinase (BTK) plays a critical role in B cell development and function. We recently described a selective BTK inhibitor, RN486, that blocks B cell receptor (BCR) and Fcγ receptor signaling and is efficacious in animal models of arthritis. The aim of this study was to examine the potential efficacy of BTK in systemic lupus erythematosus (SLE), using an NZB × NZW mouse model of spontaneous SLE.

METHODS

Mice received RN486 or its vehicle (administered in chow) at a final concentration of 30 mg/kg for 8 weeks, starting at 32 weeks of age.

RESULTS

The administration of RN486 completely stopped disease progression, as determined by histologic and functional analyses of glomerular nephritis. The efficacy was associated with striking inhibition of B cell activation, as demonstrated by a significant reduction in CD69 expression in response to BCR crosslinking. RN486 markedly reduced the secretion of IgG anti-double-stranded DNA (anti-dsDNA) secretion, as determined by enzyme-linked immunosorbent and enzyme-linked immunospot assays. Flow cytometric analysis demonstrated depletion of CD138(high) B220(low) plasma cells in the spleen. RN486 inhibited secretion of IgG anti-dsDNA but not IgM anti-dsDNA, suggesting that pharmacologic blockade of BTK resembles the reported transgenic expression of low levels of endogenous BTK in B cells. In addition, RN486 may also impact the effector function of autoantibodies, as evidenced by a significant reduction in immune complex-mediated activation of human monocytes in vitro and down-regulation of the expression of macrophage-related and interferon-inducible genes in both the kidneys and spleens of treated mice.

CONCLUSION

Collectively, our data suggest that BTK inhibitors may simultaneously target autoantibody-producing and effector cells in SLE, thus constituting a promising therapeutic alternative for this disease.

Anti-tumor necrosis factor α treatment of interferon-α-induced murine lupus nephritis reduces the renal macrophage response but does not alter glomerular immune complex formation

OBJECTIVE

To analyze the mechanism for the therapeutic effects of tumor necrosis factor α (TNFα) inhibition in a murine model of systemic lupus erythematosus.

METHODS

We used the (NZB × NZW)F(1) (NZB/NZW) mouse model of interferon-α-induced lupus nephritis and treated mice with TNF receptor type II (TNFRII) Ig after TNFα expression was detected in the kidneys. Autoantibodies were measured by enzyme-linked immunosorbent assay (ELISA), and autoantibody- forming cells were determined using an enzyme-linked immunospot assay. Activation of splenocytes was analyzed by flow cytometry. Kidneys were harvested and analyzed using flow cytometry, immunohistochemistry, ELISA, Western blotting, and real-time polymerase chain reaction.

RESULTS

TNFRII Ig treatment stabilized nephritis and markedly prolonged survival. Autoantibody production and systemic immune activation were not inhibited, but the renal response to glomerular immune complex deposition was attenuated. This was associated with decreases in renal production of chemokines, renal endothelial cell activation, interstitial F4/80(high) macrophage accumulation, tubular damage, and oxidative stress. In contrast, perivascular lymphoid aggregates containing B cells, T cells, and dendritic cells accumulated unabated.

CONCLUSION

Our data suggest that TNFα is a critical cytokine that amplifies the response of the nephron to immune complex deposition, but that it has less influence on the response of the systemic vasculature to inflammation.

Cross-species transcriptional network analysis defines shared inflammatory responses in murine and human lupus nephritis

Lupus nephritis (LN) is a serious manifestation of systemic lupus erythematosus. Therapeutic studies in mouse LN models do not always predict outcomes of human therapeutic trials, raising concerns about the human relevance of these preclinical models. In this study, we used an unbiased transcriptional network approach to define, in molecular terms, similarities and differences among three lupus models and human LN. Genome-wide gene-expression networks were generated using natural language processing and automated promoter analysis and compared across species via suboptimal graph matching. The three murine models and human LN share both common and unique features. The 20 commonly shared network nodes reflect the key pathologic processes of immune cell infiltration/activation, endothelial cell activation/injury, and tissue remodeling/fibrosis, with macrophage/dendritic cell activation as a dominant cross-species shared transcriptional pathway. The unique nodes reflect differences in numbers and types of infiltrating cells and degree of remodeling among the three mouse strains. To define mononuclear phagocyte-derived pathways in human LN, gene sets activated in isolated NZB/W renal mononuclear cells were compared with human LN kidney profiles. A tissue compartment-specific macrophage-activation pattern was seen, with NF-κB1 and PPARγ as major regulatory nodes in the tubulointerstitial and glomerular networks, respectively. Our study defines which pathologic processes in murine models of LN recapitulate the key transcriptional processes active in human LN and suggests that there are functional differences between mononuclear phagocytes infiltrating different renal microenvironments.

IFN-α confers resistance of systemic lupus erythematosus nephritis to therapy in NZB/W F1 mice

The critical role of IFN-α in the pathogenesis of human systemic lupus erythematosus has been highlighted in recent years. Exposure of young lupus-prone NZB/W F1 mice to IFN-α in vivo leads to an accelerated lupus phenotype that is dependent on T cells and is associated with elevated serum levels of BAFF, IL-6, and TNF-α, increased splenic expression of IL-6 and IL-21, formation of large germinal centers, and the generation of large numbers of short-lived plasma cells that produce IgG2a and IgG3 autoantibodies. In this study, we show that both IgG2a and IgG3 autoantibodies are pathogenic in IFN-α-accelerated lupus, and their production can be dissociated by using low-dose CTLA4-Ig. Only high-dose CTLA4-Ig attenuates both IgG2a and IgG3 autoantibody production and significantly delays death from lupus nephritis. In contrast, BAFF/APRIL blockade has no effect on germinal centers or the production of IgG anti-dsDNA Abs but, if given at the time of IFN-α challenge, delays the progression of lupus by attenuating systemic and renal inflammation. Temporary remission of nephritis induced by combination therapy with cyclophosphamide, anti-CD40L Ab, and CTLA4-Ig is associated with the abrogation of germinal centers and depletion of short-lived plasma cells, but relapse occurs more rapidly than in conventional NZB/W F1 mice. This study demonstrates that IFN-α renders NZB/W F1 relatively resistant to therapeutic intervention and suggests that the IFN signature should be considered when randomizing patients into groups and analyzing the results of human clinical trials in systemic lupus erythematosus.

A unique hybrid renal mononuclear phagocyte activation phenotype in murine systemic lupus erythematosus nephritis

Renal infiltration with mononuclear cells is associated with poor prognosis in systemic lupus erythematosus. A renal macrophage/dendritic cell signature is associated with the onset of nephritis in NZB/W mice, and immune-modulating therapies can reverse this signature and the associated renal damage despite ongoing immune complex deposition. In nephritic NZB/W mice, renal F4/80(hi)/CD11c(int) macrophages are located throughout the interstitium, whereas F4/80(lo)/CD11c(hi) dendritic cells accumulate in perivascular lymphoid aggregates. We show here that F4/80(hi)/CD11c(int) renal macrophages have a Gr1(lo)/Ly6C(lo)/VLA4(lo)/MHCII(hi)/CD43(lo)/CD62L(lo) phenotype different from that described for inflammatory macrophages. At nephritis onset, F4/80(hi)/CD11c(int) cells upregulate cell surface CD11b, acquire cathepsin and matrix metalloproteinase activity, and accumulate large numbers of autophagocytic vacuoles; these changes reverse after the induction of remission. Latex bead labeling of peripheral blood Gr1(lo) monocytes indicates that these are the source of F4/80(hi)/CD11c(int) macrophages. CD11c(hi)/MHCII(lo) dendritic cells are found in the kidneys only after proteinuria onset, turnover rapidly, and disappear rapidly after remission induction. Gene expression profiling of the F4/80(hi)/CD11c(int) population displays increased expression of proinflammatory, regulatory, and tissue repair/degradation-associated genes at nephritis onset that reverses with remission induction. Our findings suggest that mononuclear phagocytes with an aberrant activation profile contribute to tissue damage in lupus nephritis by mediating both local inflammation and excessive tissue remodeling.

Selective blockade of BAFF for the prevention and treatment of systemic lupus erythematosus nephritis in NZM2410 mice

OBJECTIVE

To determine whether BAFF or combined BAFF/APRIL blockade is effective in a mouse model of systemic lupus erythematosus (SLE) nephritis characterized by rapidly progressive glomerulosclerosis.

METHODS

NZM2410 mice at early and late stages of SLE nephritis were treated with a short course of BAFF-R-Ig or TACI-Ig fusion protein. Proteinuria and serologic profile were evaluated every 2 weeks. Immunohistochemical, flow cytometric, and enzyme-linked immunospot analyses of the spleen, kidney, and bone marrow were performed after 8 weeks and after 33 weeks.

RESULTS

A short course of selective blockade of BAFF alone was sufficient to prevent and treat SLE nephritis in NZM2410 mice, despite the formation of pathogenic autoantibodies. Decreases in spleen size and B cell depletion persisted for more than 33 weeks after treatment and resulted in secondary decreases in CD4 memory T cell formation and activation of splenic and peripheral monocytes. Immune complex deposition in the kidneys was dissociated from renal damage and from activation of renal endothelial and resident dendritic cells.

CONCLUSION

Selective blockade of BAFF alone, which resulted in B cell depletion and splenic collapse, was sufficient to prevent and treat the disease in this model of noninflammatory SLE nephritis. This shows that the inflammatory microenvironment may be a determinant of the outcome of B cell modulation strategies.

Prevention of murine antiphospholipid syndrome by BAFF blockade

OBJECTIVE

This study was undertaken to determine whether BAFF blockade can be used to prevent or treat antiphospholipid syndrome in a mouse model.

METHODS

Eight- and 12-week-old (NZW x BXSB)F(1) mice were treated with BAFF-R-Ig or TACI-Ig alone or in addition to a short course of CTLA-4Ig. Mice were monitored for thrombocytopenia and proteinuria. Sera were tested for anticardiolipin antibodies (aCL), BAFF levels, and levels of soluble vascular cell adhesion molecule and E-selectin. Mice were killed at 17, 22, or 32 weeks of age, and kidneys and hearts were subjected to histologic examination. Spleen cells were phenotyped and enzyme-linked immunospot assays for autoantibody-producing B cells were performed.

RESULTS

Both BAFF-R-Ig and TACI-Ig prevented disease onset and significantly prolonged survival. Treated mice had significantly smaller spleens than controls, with fewer B cells and fewer activated and memory T cells. BAFF blockade did not prevent the development of aCL, and there was only a modest delay in the development of thrombocytopenia. However, treated mice had significantly less nephritis and myocardial infarcts than did controls.

CONCLUSION

Our findings suggest that aCL are generated in the germinal center, which is relatively independent of BAFF. Effector function of antiplatelet antibodies was only modestly affected by BAFF blockade. In contrast, myocardial infarctions were prevented, suggesting that triggering of thromboses requires both autoantibodies and mediators of inflammation. Similarly, renal damage requires both immune complexes and effector cells. The dissociation between autoantibody production and inflammation that may occur with B cell-depleting therapies underscores the role of B cells as effector cells in the autoimmune response.

Enhanced selection of high affinity DNA-reactive B cells following cyclophosphamide treatment in mice

A major goal for the treatment of patients with systemic lupus erythematosus with cytotoxic therapies is the induction of long-term remission. There is, however, a paucity of information concerning the effects of these therapies on the reconstituting B cell repertoire. Since there is recent evidence suggesting that B cell lymphopenia might attenuate negative selection of autoreactive B cells, we elected to investigate the effects of cyclophosphamide on the selection of the re-emerging B cell repertoire in wild type mice and transgenic mice that express the H chain of an anti-DNA antibody. The reconstituting B cell repertoire in wild type mice contained an increased frequency of DNA-reactive B cells; in heavy chain transgenic mice, the reconstituting repertoire was characterized by an increased frequency of mature, high affinity DNA-reactive B cells and the mice expressed increased levels of serum anti-DNA antibodies. This coincided with a significant increase in serum levels of BAFF. Treatment of transgene-expressing mice with a BAFF blocking agent or with DNase to reduce exposure to autoantigen limited the expansion of high affinity DNA-reactive B cells during B cell reconstitution. These studies suggest that during B cell reconstitution, not only is negative selection of high affinity DNA-reactive B cells impaired by increased BAFF, but also that B cells escaping negative selection are positively selected by autoantigen. There are significant implications for therapy.

Interferon-alpha treatment of female (NZW x BXSB)F(1) mice mimics some but not all features associated with the Yaa mutation

OBJECTIVE

Male (NZW x BXSB)F(1) mice develop antiphospholipid syndrome (APS) and proliferative glomerulonephritis that is markedly accelerated by the Yaa locus encoding an extra copy of Tlr7. Female (NZW x BXSB)F(1) mice with only 1 active copy of Tlr7 develop late-onset glomerulonephritis but not APS. Because a major function of Toll-like receptor 7 is to induce type I interferons (IFNs), our goal was to determine whether IFNalpha can induce or accelerate the manifestations of systemic lupus erythematosus (SLE) in female (NZW x BXSB)F(1) mice.

METHODS

Eight-week-old female (NZW x BXSB)F(1) mice were injected with a single dose of adenovirus expressing IFNalpha. Mice were monitored for the development of thrombocytopenia and proteinuria. Sera were tested for anticardiolipin and anti-Sm/RNP antibodies. Mice were killed at 17 or 22 weeks of age, and their kidneys and hearts were examined histologically and by immunohistochemistry. Spleen cells were phenotyped, and enzyme-linked immunospot assays for autoantibody-producing B cells were performed.

RESULTS

IFNalpha markedly accelerated nephritis and death in female (NZW x BXSB)F(1) mice. A significant increase in spleen cell numbers associated with a striking increase in the number of activated B and T cells was observed. Marginal-zone B cells were retained. IFNalpha-induced increased titers of autoantibodies were observed, but thrombocytopenia was not observed. Cardiac damage was milder than that in male mice.

CONCLUSION

IFNalpha accelerates the development of renal inflammatory disease in female (NZW x BXSB)F(1) mice but induces only mild APS and does not induce thrombocytopenia. The effect of IFNalpha on SLE disease manifestations is strain dependent. These findings are relevant to our understanding of the physiologic significance of the IFN signature.

BAFF blockade for systemic lupus erythematosus: will the promise be fulfilled?

SUMMARY

Systemic lupus erythematosus (SLE) is a complex immune disorder in which loss of tolerance to nucleic acid antigens and other cross-reactive antigens is associated with the development of pathogenic autoantibodies that damage target organs including the skin, joints, brain, and kidney. B cells are essential to lupus pathogenesis, not only because they produce pathogenic autoantibodies but also because they have multiple effector functions in the immune system. There has been much recent interest therefore in targeting of B cells for the treatment of SLE and other autoimmune diseases. BAFF (B-cell activation factor belonging to the tumor necrosis factor family) is a crucial homeostatic cytokine for B cells that is upregulated during inflammation and links adaptive with innate immunity. Excessive levels of BAFF may alter selection of autoreactive B cells and contribute to perpetuation of SLE by a variety of mechanisms. BAFF antagonists have been effective in the prevention and treatment of SLE in several different murine models. Three classes of BAFF antagonists have been developed for clinical use, and initial clinical trials have begun. However, immune modulation in SLE is complicated by differences in the immune defects between patients and at different disease stages. Further work will be needed both in animal models and humans to determine the most appropriate clinical applications for BAFF blockade.

Enhanced selection of high affinity DNA-reactive B cells following cyclophosphamide treatment (99.40)

A major goal for the treatment of SLE patients with cytotoxic therapies is the induction of long term remission. There is, however, a paucity of information concerning the effects of these therapies on the reconstituting B cell repertoire. Since there is recent evidence suggesting that B cell lymphopenia might attenuate negative selection of autoreactive B cells, we elected to investigate the effects cyclophosphamide (CY) on the selection of the re-emerging B cell repertoire in transgenic mice that express the H chain of an anti-DNA antibody (R4A-Tg).

The reconstituting B cell repertoire contained an increased frequency of mature, high affinity DNA-reactive B cells as determined by single cell PCR analysis, and the mice expressed increased levels of serum anti-DNA antibodies. This coincided with a significant increase in levels of BAFF, a B cell survival factor. Treatment with BAFF-R-Ig, a BAFF blocking agent or with DNase, to reduce exposure to autoantigen, limited the expansion of high affinity DNA-reactive B cells during B cell reconstitution. These studies suggest that during B cell reconstitution, negative selection of high affinity DNA-reactive B cells is impaired by increased BAFF. B cells escaping negative selection are positively selected by autoantigen. BAFF blockade following treatment with B cell depleting agents may be useful for the successful long-term remission of SLE.

Activated renal macrophages are markers of disease onset and disease remission in lupus nephritis

Costimulatory blockade with CTLA4Ig and anti-CD40L along with a single dose of cyclophosphamide induces remission of systemic lupus erythematosus nephritis in NZB/W F(1) mice. To understand the mechanisms for remission and for impending relapse, we examined the expression profiles of 61 inflammatory molecules in the perfused kidneys of treated mice and untreated mice at different stages of disease. Further studies using flow cytometry and immunohistochemistry allowed us to determine the cellular origins of several key markers. We show that only a limited set of inflammatory mediators is expressed in the kidney following glomerular immune complex deposition but before the onset of proteinuria. Formation of a lymphoid aggregate in the renal pelvis precedes the invasion of the kidney by inflammatory cells. Regulatory molecules are expressed early in the disease process and during remission but do not prevent the inevitable progression of active inflammation. Onset of proliferative glomerulonephritis and proteinuria is associated with activation of the renal endothelium, expression of chemokines that mediate glomerular cell infiltration, and infiltration by activated dendritic cells and macrophages that migrate to different topographical areas of the kidney but express a similar profile of inflammatory cytokines. Increasing interstitial infiltration by macrophages and progressive tubular damage, manifested by production of lipocalin-2, occur later in the disease process. Studies of treated mice identify a type II (M2b)-activated macrophage as a marker of remission induction and impending relapse and suggest that therapy for systemic lupus erythematosus nephritis should include strategies that prevent both activation of monocytes and their migration to the kidney.

Similarities and differences between selective and nonselective BAFF blockade in murine SLE

B cells have multiple roles in immune activation and inflammation separate from their capacity to produce antibodies. B cell depletion is currently under intense investigation as a therapeutic strategy for autoimmune diseases. The TNF family members B cell-activating factor of the TNF family (BAFF) and its homolog A proliferation-inducing ligand (APRIL) are B cell survival and differentiation factors and are therefore rational therapeutic targets. We compared the effects of BAFF receptor-Ig, which blocks only BAFF, with those of transmembrane activator and calcium modulator ligand interactor-Ig, which blocks both BAFF and APRIL, in a murine SLE model. Both reagents prolonged the life of NZB/W F1 mice when given either before or after disease onset. Many immunologic effects of the 2 reagents were similar, including B cell and B cell subset depletion and prevention of the progressive T cell activation and dendritic cell accumulation that occurs with age in NZB/W mice without substantial effects on the emergence of the IgG anti-double-stranded DNA response. Furthermore, both reagents inhibited the T cell-independent marginal zone B cell response to particulate antigen delivered i.v., but not the B1 B cell response to the same antigen delivered i.p. In contrast, blockade of both BAFF and APRIL, but not blockade of BAFF alone, reduced the serum levels of IgM antibodies, decreased the frequency of plasma cells in the spleen, and inhibited the IgM response to a T cell-dependent antigen. The differences between selective and nonselective BAFF blockade are relevant to the choice of a BAFF blocking agent for the treatment of autoimmune and malignant diseases.

Mechanism of Action of Transmembrane Activator and Calcium Modulator Ligand Interactor-Ig in Murine Systemic Lupus Erythematosus

B cell-activating factor belonging to the TNF family (BAFF) blockade prevents the onset of disease in systemic lupus erythematosus (SLE)-prone NZB/NZW F(1) mice. To determine the mechanism of this effect, we administered a short course of TACI-Ig with and without six doses of CTLA4-Ig to 18- to 20-wk-old NZB/NZW F(1) mice and evaluated the effect on B and T cell subsets and on anti-dsDNA Ab-producing B cells. Even a brief exposure to TACI-Ig had a beneficial effect on murine SLE; CTLA4-Ig potentiated this effect. The combination of TACI-Ig and CTLA4-Ig resulted in a temporary decrease in serum IgG levels. However, after cessation of treatment, high titers of IgG anti-dsDNA Abs appeared in the serum and IgG Abs deposited in the kidneys. Despite the appearance of pathogenic autoantibodies, the onset of proteinuria was markedly delayed; this was associated with prolonged depletion of B cells past the T1 stage, a decrease in the size of the spleen and lymph nodes, and a decrease in the absolute number of activated and memory CD4(+) T cells. TACI-Ig treatment normalized serum levels of IgM that are markedly elevated in NZB/W F(1) mice; this appeared to be due to a prolonged effect on the ability of the splenic microenvironment to support short-lived IgM plasma cells. Finally, a short course of combination TACI-Ig and CTLA4-Ig prolonged life and even reversed proteinuria in aged NZB/W F(1) mice, suggesting that BAFF blockade may be an effective therapeutic strategy for active SLE.

The current status of targeting BAFF/BLyS for autoimmune diseases

It is increasingly recognized that B cells have multiple functions that contribute to the pathogenesis of autoimmunity. Specific targeting of B cells might therefore be an appropriate therapeutic intervention. The tumor necrosis factor-like molecule BAFF (BLyS) is a key B cell survival factor and its receptors are expressed on most peripheral B cells. Several different BAFF antagonists are under development and in early clinical trials. We review here the rationale for BAFF blockade, and its predicted mechanism of action in autoimmune diseases.

Lowering anti-dsDNA antibodies--what's new?

Antibodies to dsDNA are specific to SLE and are pathogenic, both due to their ability to deposit in tissues through a variety of mechanisms, and to their ability, when present in immune complexes, to activate inflammatory cells. The relationship of serum anti-dsDNA antibody levels to disease activity is a complex one and the factors that determine whether or not such antibodies will be pathogenic in an individual SLE patient are incompletely understood. Although anti-dsDNA antibodies can be made by naïve B cells and B cells belonging to the B1 and marginal zone subsets, pathogenic anti-dsDNA antibodies have the hallmarks of germinal center development and exposure to T cell help, including accumulation of somatic mutations and class switching to the IgG isotype. Epitope spreading may result in aquisition of cross-reactivities with multiple target organ antigens and aquisition of a memory phenotype will allow these B cells to acquire antigen presentation functions that amplify the autoreactive response. In the early stages of disease, or after remission induction protocols, autoreactive B cells may be susceptible to treatments that target T cell costimulation or that deplete or tolerize naïve and mature B cells. Therapeutic approaches targeting innate immune responses or regulatory T cells are starting to be tested in pre-clinical models. In later disease stages, memory and plasma cell accumulation may render patients more resistant to this type of therapeutic approach. Deposition of anti-dsDNA antibodies in target tissues can stimulate an inflammatory cascade that leads to tissue damage. A number of murine models have now been developed that show that interruption of this cascade can prevent or reverse such damage. This type of approach may be beneficial for individuals with established disease. As we learn more about the specific defects that cause SLE, it may become possible to individualize therapy based on patient specific biologic markers.

Co-stimulatory blockade in the treatment of murine systemic lupus erythematosus (SLE)

Although the life span of patients with systemic lupus erythematosus (SLE) has improved considerably over the last several decades, the toxicities of chronic immunosuppressive therapy are major causes of morbidity and mortality. Safer and more effective therapies for SLE are clearly needed. SLE is characterized by excessive activation of both B and T lymphocytes. Activation of these cells requires both antigen engagement and co-stimulatory signals from interacting lymphocytes (Carreno, B.M. M. Collins, 2002, Annu. Rev. Immunol. 20: 29-53; Grewal, I.S. R.A. Flavell, 1998, Annu. Rev. Immunol. 16: 111-135). Thus, blockade of co-stimulatory signals offers a new therapeutic approach to SLE. Our short-term goal has been to understand the effect of co-stimulatory blocking reagents on the development, selection, and activation of pathogenic anti-dsDNA antibody producing B cells in mice genetically pre-determined to develop SLE and showing signs of either early or advanced disease activity. Our long-term goal is to use the knowledge we gain to design therapeutic regimens for humans that avoid the complications of long-term immunosuppression. As new co-stimulatory molecules are discovered, studying their mechanism of action in animal models and their clinical utility in human autoimmune disease should lead both to a new understanding of disease pathogenesis and also to safer and more effective therapies.

Effect of site-directed asparagine to isoleucine substitutions at the N-linked E1 glycosylation sites on rubella virus viability

The role of three N-linked glycosylation sites in rubella virus (RV) E1 protein on virion release was analyzed by transfecting Vero 76 cells with infectious RV RNA (Robo302WT) containing isoleucine substitutions at N76, N177, and N209 (individually and in combinations). RV RNAs were detected and found to retain substitutions in the transfected cells, but RV capsid indicative of infection was undetectable, except for in Robo302WT and Robo302-N177I transfected cells. Only culture supernatants of Robo302WT and Robo302-N177I RNA transfected cells were positive for RV, suggestive of the virion release into the culture medium. Further, detection of intracellular RV E1 and newly released virion-associated E1 was possible only from cells previously incubated with Robo302-N177I and Robo302WT culture supernatants, suggesting that N177I substituted virus retained infectivity. These results suggest that while glycosylation at N177 is not critical, N76I and N209I mutations are lethal to RV viability.

Rubella virus glycoprotein interaction with the endoplasmic reticulum calreticulin and calnexin

Very little is known about the cellular factors that are required for the maturation of rubella virus glycoproteins (E2 and E1) in the endoplasmic reticulum of the infected cell. In the present study, we established the interaction of the ER chaperone proteins, calreticulin and calnexin, with the RV E1 and E2 proteins in cells stably expressing the viral proteins. The interaction between E2 and calnexin was significantly higher than with calreticulin. In pulse-chase experiments, the half-life of the E2-calnexin was >45 min, whereas the half-life of the calreticulin-E2 interaction was approximately 10 min. Tunicamycin and castanospermine treatments altered the mobilities of intracellular E1 and E2, due to either lack of oligosaccharide ligand addition or trimming of terminal glucose residues, respectively. Further, the drug treatments resulted in a loss of E1 and E2 interaction with calreticulin or calnexin, thereby demonstrating that the interaction is through monoglucosylated forms of RV proteins. These studies suggest that the interaction of RV glycoproteins with the ER chaperone proteins is essential for their maturation in the endoplasmic reticulum.