Structural Remodeling of the Human Colonic Mesenchyme in Inflammatory Bowel Disease.

Intestinal mesenchymal cells play essential roles in epithelial homeostasis, matrix remodeling, immunity, and inflammation. But the extent of heterogeneity within the colonic mesenchyme in these processes remains unknown. Using unbiased single-cell profiling of over 16,500 colonic mesenchymal cells, we reveal four subsets of fibroblasts expressing divergent transcriptional regulators and functional pathways, in addition to pericytes and myofibroblasts. We identified a niche population located in proximity to epithelial crypts expressing SOX6, F3 (CD142), and WNT genes essential for colonic epithelial stem cell function. In colitis, we observed dysregulation of this niche and emergence of an activated mesenchymal population. This subset expressed TNF superfamily member 14 (TNFSF14), fibroblastic reticular cell-associated genes, IL-33, and Lysyl oxidases. Further, it induced factors that impaired epithelial proliferation and maturation and contributed to oxidative stress and disease severity in vivo. Our work defines how the colonic mesenchyme remodels to fuel inflammation and barrier dysfunction in IBD.

Self-reactive IgE exacerbates interferon responses associated with autoimmunity.

Canonically, immunoglobulin E (IgE) mediates allergic immune responses by triggering mast cells and basophils to release histamine and type 2 helper cytokines. Here we found that in human systemic lupus erythematosus (SLE), IgE antibodies specific for double-stranded DNA (dsDNA) activated plasmacytoid dendritic cells (pDCs), a type of cell of the immune system linked to viral defense, which led to the secretion of substantial amounts of interferon-α (IFN-α). The concentration of dsDNA-specific IgE found in patient serum correlated with disease severity and greatly potentiated pDC function by triggering phagocytosis via the high-affinity FcɛRI receptor for IgE, followed by Toll-like receptor 9 (TLR9)-mediated sensing of DNA in phagosomes. Our findings expand the known pathogenic mechanisms of IgE-mediated inflammation beyond those found in allergy and demonstrate that IgE can trigger interferon responses capable of exacerbating self-destructive autoimmune responses.

Noncanonical autophagy is required for type I interferon secretion in response to DNA-immune complexes.

Toll-like receptor-9 (TLR9) is largely responsible for discriminating self from pathogenic DNA. However, association of host DNA with autoantibodies activates TLR9, inducing the pathogenic secretion of type I interferons (IFNs) from plasmacytoid dendritic cells (pDCs). Here, we found that in response to DNA-containing immune complexes (DNA-IC), but not to soluble ligands, IFN-α production depended upon the convergence of the phagocytic and autophagic pathways, a process called microtubule-associated protein 1A/1B-light chain 3 (LC3)-associated phagocytosis (LAP). LAP was required for TLR9 trafficking into a specialized interferon signaling compartment by a mechanism that involved autophagy-related proteins, but not the conventional autophagic preinitiation complex, or adaptor protein-3 (AP-3). Our findings unveil a new role for nonconventional autophagy in inflammation and provide one mechanism by which anti-DNA autoantibodies, such as those found in several autoimmune disorders, bypass the controls that normally restrict the apportionment of pathogenic DNA and TLR9 to the interferon signaling compartment.

Depleting plasmacytoid dendritic cells reduces local type I interferon responses and disease activity in patients with cutaneous lupus.

Plasmacytoid dendritic cells (pDCs) not only are specialized in their capacity to secrete large amounts of type I interferon (IFN) but also serve to enable both innate and adaptive immune responses through expression of additional proinflammatory cytokines, chemokines, and costimulatory molecules. Persistent activation of pDCs has been demonstrated in a number of autoimmune diseases. To evaluate the potential benefit of depleting pDCs in autoimmunity, a monoclonal antibody targeting the pDC-specific marker immunoglobulin-like transcript 7 was generated. This antibody, known as VIB7734, which was engineered for enhanced effector function, mediated rapid and potent depletion of pDCs through antibody-dependent cellular cytotoxicity. In cynomolgus monkeys, treatment with VIB7734 reduced pDCs in blood below the lower limit of normal by day 1 after the first dose. In two phase 1 studies in patients with autoimmune diseases, VIB7734 demonstrated an acceptable safety profile, comparable to that of placebo. In individuals with cutaneous lupus, VIB7734 profoundly reduced both circulating and tissue-resident pDCs, with a 97.6% median reduction in skin pDCs at study day 85 in VIB7734-treated participants. Reductions in pDCs in the skin correlated with a decrease in local type I IFN activity as well as improvements in clinical disease activity. Biomarker analysis suggests that responsiveness to pDC depletion therapy may be greater among individuals with high baseline type I IFN activity, supporting a central role for pDCs in type I IFN production in autoimmunity and further development of VIB7734 in IFN-associated diseases.

SLE Plasma Profiling Identifies Unique Signatures of Lupus Nephritis and Discoid Lupus.

Systemic lupus erythematosus (SLE) impacts multiple organ systems, although the causes of many individual SLE pathologies are poorly understood. This study was designed to elucidate organ-specific inflammation by identifying proteins that correlate with SLE organ involvement and to evaluate established biomarkers of disease activity across a diverse patient cohort. Plasma proteins and autoantibodies were measured across seven SLE manifestations. Comparative analyses between pathologies and correlation with the SLE Disease Activity Index (SLEDAI) were used to identify proteins associated with organ-specific and composite disease activity. Established biomarkers of composite disease activity, SLE-associated antibodies, type I interferon (IFN), and complement C3, correlated with composite SLEDAI, but did not significantly associate with many individual SLE pathologies. Two clusters of proteins were associated with renal disease in lupus nephritis samples. One cluster included markers of infiltrating leukocytes and the second cluster included markers of tissue remodelling. In patients with discoid lupus, a distinct signature consisting of elevated immunoglobulin A autoantibodies and interleukin-23 was observed. Our findings indicate that proteins from blood samples can be used to identify protein signatures that are distinct from established SLE biomarkers and SLEDAI and could be used to conveniently monitor multiple inflammatory pathways present in different organ systems.

Pathogenic mechanisms of IgE-mediated inflammation in self-destructive autoimmune responses.

Autoantibodies of the IgG subclass are pathogenic in a number of autoimmune disorders such as systemic lupus erythomatosus. The presence of circulating IgE autoantibodies in autoimmune patients has also been known for almost 40 years. Despite their role in allergies, IgE autoantibodies are not associated with a higher rate of atopy in these patients. However, recently they have been recognized as active drivers of autoimmunity through mechanisms involving the secretion of Type I interferons by plasmacytoid dendritic cells (pDC), the recruitment of basophils to lymph nodes, and the activation of adaptive immune responses through B and T cells. Here, we will review the formation, prevalence, affinity, and roles of the IgE autoantibodies that have been described in autoimmunity. We also present novel evidence supporting that triggering of IgE receptors in pDC induces LC3-associated phagocytosis, a cellular process also known as LAP that is associated with interferon responses. The activation of pDC with immune complexes formed by DNA-specific IgE antibodies also induce potent B-cell differentiation and plasma cell formation, which further define IgE's role in autoimmune humoral responses.

Role of SLC11A1 (formerly NRAMP1) in regulation of signal transduction induced by Toll-like receptor 7 ligands.

Modulation of immune responses using Toll-like receptor (TLR) ligands is fast becoming one of the main new approaches for the treatment of infectious and allergic diseases. Characterizing the role of genetic factors in modulating responses to these ligands will be crucial in determining the efficacy of a particular treatment. Our previous findings have shown that treatment of Mycobacterium bovis BCG infection with a synthetic TLR7 ligand resulted in a reduction of the splenic bacterial load only in mice carrying a wild-type allele of Nramp1. To understand further how natural resistance-associated macrophage protein 1 (NRAMP1) modulates responses to TLR7 ligands, we have analysed various important TLR7 signal transduction events in macrophage cell lines derived from B10.ANramp1r and B10.ANramp1-/- mice. The Nramp1 genotype did not affect TLR7 receptor expression, ligand uptake or intracellular processing. Following TLR7 ligand stimulation, p38 mitogen-activated protein kinase (MAPK) activation was significantly reduced in B10A.Nramp1-/- macrophages compared with B10A.Nramp1r cells. Interestingly, levels of protein kinase C zeta (PKCzeta) activation were also found to be lower in B10A.Nramp1-/- macrophages and inhibition of this kinase in B10A.Nramp1r cells led to a reduction in cytokine production. Taken together, the data demonstrate a role for NRAMP1 in modulating p38 MAPK and PKCzeta activity, which leads to reduced cytokine induction by TLR7 ligands.

Noncanonical autophagy: one small step for LC3, one giant leap for immunity.

Noncanonical autophagy is utilized by phagocytes to kill and digest extracellular pathogens. This process is initiated at the cell surface by receptors that recruit elements of the autophagy machinery, like LC3, to the phagosome. Also known as LC3-associated phagocytosis, the intersection of autophagy and phagocytosis was initially described as a pathway that limits the proliferation of engulfed pathogens by expediting phagosome maturation. Emerging evidences suggest that this pathway confers previously unsuspected versatility to the immune response as it regulates functions like the interferon pathway, dead cell clearance, and antigen presentation. Here we review recent advances in understanding the functional consequences of linking the autophagy machinery to phagocytosis in innate immunity.

The nuclear autoantigen CENP-B displays cytokine-like activities toward vascular smooth muscle cells.

OBJECTIVE: A growing number of intracellular autoantigenic polypeptides have been found to play a second biologic role when they are present in the extracellular medium. We undertook this study to determine whether the CENP-B nuclear autoantigen could be added to this set of bifunctional molecules. METHODS: Purified CENP-B or CENP-B released from apoptotic cells was tested for surface binding to a number of human cell types by cell-based enzyme-linked immunosorbent assay, flow cytometry, and indirect immunofluorescence. The biologic effects of CENP-B on the migration, interleukin secretion, and signaling pathways of its specific target cells were evaluated. RESULTS: CENP-B was found to bind specifically to the surface of human pulmonary artery smooth muscle cells (SMCs) and not to fibroblasts or endothelial cells (ECs). Furthermore, CENP-B bound preferentially to SMCs of the contractile type rather than to SMCs of the synthetic type. Binding of CENP-B to SMCs stimulated their migration during in vitro wound healing assays, as well as their secretion of interleukins 6 and 8. The mechanism by which CENP-B mediated these effects involved the focal adhesion kinase, Src, ERK-1/2, and p38 MAPK pathways. Finally, CENP-B released from apoptotic ECs was found to bind to SMCs, thus indicating a plausible in vivo source of extracellular CENP-B. CONCLUSION: These novel biologic roles of the nuclear autoantigen CENP-B open up a new perspective for studying the pathogenic role of anti-CENP-B autoantibodies.

DNA topoisomerase I binding to fibroblasts induces monocyte adhesion and activation in the presence of anti-topoisomerase I autoantibodies from systemic sclerosis patients.

OBJECTIVE: Systemic sclerosis (SSc) is an autoimmune disease characterized by fibrosis due to excessive and dysregulated collagen production by fibroblasts. Previously, we reported that anti-DNA topoisomerase I (anti-topo I) antibodies bound specifically to fibroblast surfaces; however, we had not identified their antigenic target. We undertook this study to characterize the target of anti-topo I antibodies on fibroblasts and the effects of their binding. METHODS: Purified topo I or topo I released from apoptotic cells was tested for surface binding to a number of human cell types by cell-based enzyme-linked immunosorbent assay, flow cytometry, and indirect immunofluorescence. Antibodies purified from SSc patient and normal control sera were used to detect topo I binding. The consequences of topo I and anti-topo I binding to fibroblasts were assessed by coculture with THP-1 monocytes. RESULTS: The autoantigen topo I itself was found to bind specifically to fibroblasts in a dose-dependent and saturable manner, where it was recognized by anti-topo I from SSc patients. The binding of anti-topo I subsequently stimulated adhesion and activation of cocultured monocytes. Topo I released from apoptotic endothelial cells was also found to bind specifically to fibroblasts. CONCLUSION: The findings of this study thus confirm and extend the findings of our previous study by showing that topo I binding to fibroblast surfaces is both necessary and sufficient for anti-topo I binding. Second, topo I-anti-topo I complex binding can then trigger the adhesion and activation of monocytes, thus providing a plausible model for the amplification of the fibrogenic cascade in anti-topo I-positive SSc patients.

Direct binding of anti-DNA topoisomerase I autoantibodies to the cell surface of fibroblasts in patients with systemic sclerosis.

OBJECTIVE: Fibroblasts play a crucial role in the development of systemic sclerosis (SSc), and antifibroblast antibodies (AFAs) capable of inducing a proinflammatory phenotype in fibroblasts have been detected in the sera of SSc patients. This study examined the prevalence of AFAs in SSc and other diseases and the possible correlation between AFAs and known antinuclear antibody specificities in SSc patients. METHODS: Sera from 99 patients with SSc, 123 patients with other autoimmune and nonautoimmune diseases, and 30 age- and sex-matched healthy controls were examined. AFA prevalence was assessed by flow cytometry and further characterized by indirect immunofluorescence, enzyme-linked immunosorbent assay (ELISA), and immunoblotting. Anti-topoisomerase I (anti-topo I) from SSc sera were purified by affinity chromatography on topo I. RESULTS: AFAs were more common in SSc patients (26.3%) than in any other disease groups studied. The presence of AFA was significantly associated with pulmonary involvement and death. AFA-positive sera from SSc patients bound to all human and rodent fibroblasts tested, but not to human primary endothelial cells or smooth muscle cells. All SSc AFAs strongly reacted with topo I by ELISA and immunoblotting. The binding intensity of SSc AFAs correlated strongly with reactivity against topo I on immunoblots of fibroblast extracts and with the immunofluorescence pattern typical of anti-topo I on permeabilized cells. Total IgG and affinity-purified anti-topo I from AFA-positive SSc sera were found to react with the surface of unpermeabilized fibroblasts by flow cytometry as well as by immunofluorescence and confocal microscopy. CONCLUSION: This is the first report establishing that AFAs in SSc are strongly correlated with anti-topo I and, furthermore, that anti-topo I antibodies themselves display AFA activity by reacting with determinants at the fibroblast surface.