Inappropriate activation of type I interferon (IFN) plays a key role in the pathogenesis of autoimmune disease, including systemic lupus erythematosus (SLE). Here we report the presence of IFN activation in SLE bone marrow (BM), as measured by an IFN gene signature, increased IFN regulated chemokines, and direct production of IFN by BM resident cells, associated with profound changes in B cell development. The majority of SLE patients had an IFN signature in the BM that was more pronounced than the paired peripheral blood (PB) and correlated with both higher autoantibodies and disease activity. Pronounced alterations in B cell development were noted in SLE in the presence of an IFN signature with a reduction in the fraction of pro/pre B cells suggesting an inhibition in early B cell development and an expansion of B cells at the transitional (T2) stage. These B cell changes strongly correlated with an increase in BAFF and APRIL expression in the IFN high BM. Furthermore, we found that BM neutrophils in SLE were prime producers of IFN-α and B cell factors. In NZM lupus-prone mice similar changes in B cell development were observed and mediated by IFN, given abrogation in NZM mice lacking type I IFN receptor. BM neutrophils were abundant, responsive to and producers of IFN, in close proximity to B cells. These results indicate that the BM is an important but previously unrecognized target organ in SLE with neutrophil mediated IFN activation and alterations in B cell ontogeny and selection.

Appropriate macrophage response to an implanted biomaterial is crucial for successful tissue healing outcomes. In this work we investigated how intrinsic topological cues from electrospun biomaterials and extrinsic mechanical loads cooperate to guide macrophage activation and macrophage-tendon fibroblast cross-talk. We performed a series of in vitro and in vivo experiments using aligned or randomly oriented polycaprolactone nanofiber substrates in both mechanically loaded and unloaded conditions. Across all experiments a disorganized biomaterial fiber topography was alone sufficient to promote a pro-inflammatory signature in macrophages, tendon fibroblasts, and tendon tissue. Extrinsic mechanical loading was found to strongly regulate the character of this signature by reducing pro-inflammatory markers both in vitro and in vivo. We observed that macrophages generally displayed a stronger response to biophysical cues than tendon fibroblasts, with dominant effects of cross-talk between these cell types observed in mechanical co-culture models. Collectively our data suggest that macrophages play a potentially important role as mechanosensory cells in tendon repair, and provide insight into how biological response might be therapeutically modulated by rational biomaterial designs that address the biomechanical niche of recruited cells.

Objective BMSCs create a special microenvironment for hematopoiesis and immunity and also display robust immunomodulatory properties which are impaired in SLE. This study was undertaken to define the mechanisms of defects in human SLE BMSCs. Methods Patients fulfilling SLE classification criteria and healthy controls were recruited under an Institutional Review Board approved protocol (n=6 each). BMSCs were isolated with low density Ficoll/Hypaque. BMSCs were verified by flow cytometry and studied using immunocytochemistry, real-time PCR, western blotting, comet assay, beta-galactosidase assay, and RNA interference. Results SLE BMSCs have a senescent phenotype characterized by reduced proliferation rate, increased production of reactive oxygen species (ROS), increased DNA damage and repair, increased expression of p53 and p16 which block the cell cycle, and altered cytokine production (increased pro-inflammatory cytokine and decreased immunomodulatory cytokine production). Moreover, SLE BMSCs have a 5 fold increase in IFNβ (p<0.05) and increased IFNβ-induced mRNAs including mRNA for the intracellular nucleic acid sensing adaptor protein MAVS whose expression was highly correlated with IFNβ levels (r > 0.9, p < 0.01). Since MAVS is known to induce IFNβ production, we hypothesized a positive feedback loop between MAVS and IFNβ. Strikingly, silencing MAVS markedly decreased IFNβ, p53, and p16 protein levels and expression of mRNAs for pro-inflammatory cytokines. Conclusions This study demonstrates a novel pathway for elevated IFNβ signaling in SLE that is not dependent on stimulation by immune complexes but rather is cell-intrinsic and critically mediated by IFNβ and MAVS, implicating new pathways as potential therapeutic targets.

Neutrophils are well characterized as mediators of peripheral tissue damage in lupus, but it remains unclear whether they influence loss of self-tolerance in the adaptive immune compartment. Lupus neutrophils produce elevated levels of factors known to fuel autoantibody production, including interleukin-6 and B cell survival factors, but also reactive oxygen intermediates, which can suppress lymphocyte proliferation. In order to assess whether neutrophils directly influence the progression of auto-reactivity in secondary lymphoid organs (SLO), we characterized the localization and cell-cell contacts of splenic neutrophils at several stages in the progression of disease in the NZB/W murine model of lupus. Neutrophils accumulate in SLO over the course of lupus progression, preferentially localizing near T lymphocytes early in disease and B cells with advanced disease. RNA sequencing reveals that the splenic neutrophil transcriptional program changes significantly over the course of disease, with neutrophil expression of anti-inflammatory mediators peaking during early- and mid-stage disease, and evidence of neutrophil activation with advanced disease. To assess whether neutrophils exert predominantly protective or deleterious effects on loss of B cell self-tolerance in vivo, we depleted neutrophils at different stages of disease. Neutrophil depletion early in lupus resulted in a striking acceleration in the onset of renal disease, SLO germinal center formation, and auto-reactive plasma cell production. In contrast, neutrophil depletion with more advanced disease did not alter SLE progression. These results demonstrate a surprising temporal and context dependent role for neutrophils in restraining auto-reactive B cell activation in lupus.