Objective Kidney involvement affects 40–60% of patients with lupus and is responsible for significant morbidity and mortality. Using depletion approaches, several studies have suggested that macrophages may play a key role in the pathogenesis of lupus nephritis. However, “off target” effects of macrophage depletion, such as altered hematopoiesis or enhanced autoantibody production, impeded the determination of a conclusive relationship. Methods In this study, we investigated the role of macrophages in mice receiving rabbit anti-glomerular antibodies, or nephrotoxic serum (NTS), an experimental model which closely mimics the immune complex mediated disease seen in murine and human lupus nephritis. GW2580, a selective inhibitor of the colony stimulating factor-1 (CSF-1) receptor kinase, was used for macrophage depletion. Results We found that GW2580-treated, NTS challenged mice did not develop the increased levels of proteinuria, serum creatinine, or serum urea seen in control-treated, NTS challenged mice. NTS challenged mice exhibited significantly increased kidney expression of inflammatory cytokines including RANTES, IP-10, VCAM-1 and iNOS, whereas GW2580-treated mice were protected from the robust expression of these inflammatory cytokines that are associated with LN. Quantification of macrophage related gene expression, flow cytometry analysis of kidney single cell suspensions, and immunofluorescence staining confirmed the depletion of macrophages in GW2580-treated mice, specifically within renal glomeruli. Conclusions Our results strongly implicate a specific and necessary role for macrophages in the development of immune glomerulonephritis mediated by pathogenic antibodies, and support the development of macrophage targeting approaches for the treatment of lupus nephritis.

TNF-like weak inducer of apoptosis (TWEAK, TNFSF12) and its sole receptor Fn14, belonging to the TNF ligand and receptor superfamilies respectively, are involved in cell survival and cytokine production. The role of TWEAK/Fn14 interactions in the pathogenesis of cutaneous lupus has not been explored. TWEAK treatment of murine PAM212 keratinocytes stimulated the secretion of RANTES via Fn14, and promoted apoptosis. Parthenolide, but not wortmanin or the MAPK inhibitor PD98059, significantly decreased production of RANTES, indicating that this effect of TWEAK is mediated via NF-κB signaling. Ultraviolet-B irradiation significantly upregulated the expression of Fn14 on keratinocytes in vitro and in vivo, and increased RANTES production. MRL/lpr Fn14 knockout lupus mice were compared with MRL/lpr Fn14 wild-type mice to evaluate for any possible differences in the severity of cutaneous lesions and the presence of infiltrating immune cells. MRL/lpr Fn14 knockout mice had markedly attenuated cutaneous disease as compared to their Fn14 wild-type littermates, as evidenced by the well maintained architecture of the skin and significantly decreased skin infiltration of T cells and macrophages. Our data strongly implicate TWEAK/Fn14 signaling in the pathogenesis of the cutaneous manifestations in the MRL/lpr model of spontaneous lupus, and suggest a possible target for therapeutic intervention.

Systemic lupus erythematosus (SLE) is a multifactorial autoimmune disease that can affect multiple end organs. Kidney and brain are two of the organs most commonly involved in SLE. Past studies have suggested the importance of macrophages in the pathogenesis of lupus nephritis (LN). Furthermore, as the immune effectors of the brain, microglia have been implicated in pathways leading to neuropsychiatric SLE (NPSLE). We depleted macrophages and microglia using GW2580, a small colony stimulating factor-1 receptor (CSF-1R) kinase inhibitor, in MRL-lpr/lpr (MRL/lpr) mice, a classic murine lupus model that displays features of both LN and NPSLE. Treatment was initiated before the onset of disease, and mice were followed for the development of LN and neurobehavioral dysfunction throughout the study. Treatment with GW2580 significantly ameliorated kidney disease, as evidenced by decreased proteinuria, BUN, and improved renal histopathology, despite equivalent levels of IgG and C3 deposition in the kidneys of treated and control mice. We were able to confirm macrophage depletion within the kidney via IBA-1 staining. Furthermore, we observed specific improvement in the depression-like behavioral deficit of MRL/lpr mice with GW2580 treatment. Circulating antibody and autoantibody levels were, however, not affected. These results provide additional support for the role of macrophages as a potentially valuable therapeutic target in SLE. Inhibiting CSF-1 receptor signaling would be more targeted than current immunosuppressive therapies, and may hold promise for the treatment of renal and neuropsychiatric end organ disease manifestations.

Lupus nephritis (LN) is a potentially dangerous end organ pathology that affects upwards of 60% of lupus 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, either prophylactically or therapeutically. When compared with control treated mice, NTS-challenged mice treated prophylactically with BI-BTK-1 exhibited significantly attenuated kidney disease, which was dose dependent. BI-BTK-1 treatment resulted in decreased 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.

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 BIBTK-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.

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

A growing body of evidence demonstrates that asymptomatic and pre-symptomatic transmission of SARS-CoV-2 is a major contributor to the COVID-19 pandemic. Frontline healthcare workers in COVID-19 hotspots have faced numerous challenges, including shortages of personal protective equipment (PPE) and difficulties acquiring clinical testing. The magnitude of the exposure of healthcare workers and the potential for asymptomatic transmission makes it critical to understand the incidence of infection in this population. To determine the prevalence of asymptomatic SARS-CoV-2 infection amongst healthcare workers, we studied frontline staff working in the Montefiore Health System in New York City. All participants were asymptomatic at the time of testing and were tested by RT-qPCR and for anti-SARS-CoV-2 antibodies. The medical, occupational, and COVID-19 exposure histories of participants were recorded via questionnaires. Of the 98 asymptomatic healthcare workers tested, 19 (19.4%) tested positive by RT-qPCR and/or ELISA. Within this group, four (4.1%) were RT-qPCR positive, and four (4.1%) were PCR and IgG positive. Notably, an additional 11 (11.2%) individuals were IgG positive without a positive PCR. Two PCR positive individuals subsequently developed COVID-19 symptoms, while all others remained asymptomatic at 2-week follow-up. These results indicate that there is considerable asymptomatic infection with SARS-CoV-2 within the healthcare workforce, despite current mitigation policies. Furthermore, presuming that asymptomatic staff are not carrying SARS-CoV-2 is inconsistent with our results, and this could result in amplified transmission within healthcare settings. Consequently, aggressive testing regiments, such as testing frontline healthcare workers on a regular, multi-modal basis, may be required to prevent further spread within the workforce and to patients.

The cytokine TWEAK and its receptor Fn14 are involved in cell survival and cytokine production. The TWEAK/Fn14 pathway plays a role in the pathogenesis of spontaneous cutaneous lesions in the MRL/lpr lupus strain; however, the role of TWEAK/Fn14 in disease induced by ultraviolet B (UVB) irradiation has not been explored. MRL/lpr Fn14 knockout (KO) were compared to MRL/lpr Fn14 wild-type (WT) mice following exposure to UVB. We found that irradiated MRL/lpr KO mice had significantly attenuated cutaneous disease when compared to their WT counterparts. There were also fewer infiltrating immune cells (CD3+, IBA-1+, and NGAL+) in the UVB-exposed skin of MRL/lpr Fn14KO mice, as compared to Fn14WT. Furthermore, we identified several macrophage-derived proinflammatory chemokines with elevated expression in MRL/lpr mice after UV exposure. Depletion of macrophages, using a CSF-1R inhibitor, was found to be protective against the development of skin lesions after UVB exposure. In combination with the phenotype of the MRL/lpr Fn14KO mice, these findings indicate a critical role for Fn14 and recruited macrophages in UVB-triggered cutaneous lupus. Our data strongly suggest that TWEAK/Fn14 signaling is important in the pathogenesis of UVB-induced cutaneous disease manifestations in the MRL/lpr model of lupus, and further support this pathway as a possible target for therapeutic intervention.