IL-10 Differentially Promotes Mast Cell Responsiveness to IL-33, Resulting in Enhancement of Type 2 Inflammation and Suppression of Neutrophilia

Mast cells (MCs) play critical roles in the establishment of allergic diseases. We recently demonstrated an unexpected, proinflammatory role for IL-10 in regulating MC responses. IL-10 enhanced MC activation and promoted IgE-dependent responses during food allergy. However, whether these effects extend to IgE-independent stimuli is not clear. In this article, we demonstrate that IL-10 plays a critical role in driving IL-33-mediated MC responses. IL-10 stimulation enhanced MC expansion and degranulation, ST2 expression, IL-13 production, and phospho-relA upregulation in IL-33-treated cells while suppressing TNF-α. These effects were partly dependent on endogenous IL-10 and further amplified in MCs coactivated with both IL-33 and IgE/Ag. IL-10's divergent effects also extended in vivo. In a MC-dependent model of IL-33-induced neutrophilia, IL-10 treatment enhanced MC responsiveness, leading to suppression of neutrophils and decreased TNF-α. In contrast, during IL-33-induced type 2 inflammation, IL-10 priming exacerbated MC activity, resulting in MC recruitment to various tissues, enhanced ST2 expression, induction of hypothermia, recruitment of eosinophils, and increased MCPT-1 and IL-13 levels. Our data elucidate an important role for IL-10 as an augmenter of IL-33-mediated MC responses, with implications during both allergic diseases and other MC-dependent disorders. IL-10 induction is routinely used as a prognostic marker of disease improvement. Our data suggest instead that IL-10 can enhance ST2 responsiveness in IL-33-activated MCs, with the potential to both aggravate or suppress disease severity depending on the inflammatory context.

The Implant-Induced Foreign Body Response Is Limited by CD13-Dependent Regulation of Ubiquitination of Fusogenic Proteins

Implanted medical devices, from artificial heart valves and arthroscopic joints to implantable sensors, often induce a foreign body response (FBR), a form of chronic inflammation resulting from the inflammatory reaction to a persistent foreign stimulus. The FBR is characterized by a subset of multinucleated giant cells (MGCs) formed by macrophage fusion, the foreign body giant cells (FBGCs), accompanied by inflammatory cytokines, matrix deposition, and eventually deleterious fibrotic implant encapsulation. Despite efforts to improve biocompatibility, implant-induced FBR persists, compromising the utility of devices and making efforts to control the FBR imperative for long-term function. Controlling macrophage fusion in FBGC formation presents a logical target to prevent implant failure, but the actual contribution of FBGCs to FBR-induced damage is controversial. CD13 is a molecular scaffold, and in vitro induction of CD13KO bone marrow progenitors generates many more MGCs than the wild type, suggesting that CD13 regulates macrophage fusion. In the mesh implant model of FBR, CD13KO mice produced significantly more peri-implant FBGCs with enhanced TGF-β expression and increased collagen deposition versus the wild type. Prior to fusion, increased protrusion and microprotrusion formation accompanies hyperfusion in the absence of CD13. Expression of fusogenic proteins driving cell-cell fusion was aberrantly sustained at high levels in CD13KO MGCs, which we show is due to a novel CD13 function, to our knowledge, regulating ubiquitin/proteasomal protein degradation. We propose CD13 as a physiologic brake limiting aberrant macrophage fusion and the FBR, and it may be a novel therapeutic target to improve the success of implanted medical devices. Furthermore, our data directly implicate FBGCs in the detrimental fibrosis that characterizes the FBR.

Astrocytic TIMP-1 regulates production of Anastellin, a novel inhibitor of oligodendrocyte differentiation and FTY720 responses

Astrocyte activation is associated with neuropathology and the production of tissue inhibitor of metalloproteinase-1 (TIMP1). TIMP1 is a pleiotropic extracellular protein that functions both as a protease inhibitor and as a growth factor. We have previously demonstrated that murine astrocytes that lack expression of Timp1 do not support rat oligodendrocyte progenitor cell (rOPC) differentiation, and adult global Timp1 knockout ( Timp1 KO ) mice do not efficiently remyelinate following a demyelinating injury. To better understand the basis of this, we performed unbiased proteomic analyses and identified a fibronectin-derived peptide called anastellin that is unique to the murine Timp1 KO astrocyte secretome. Anastellin was found to block rOPC differentiation in vitro and enhanced the inhibitory influence of fibronectin on rOPC differentiation. Anastellin is known to act upon the sphingosine-1-phosphate receptor 1 (S1PR1), and we determined that anastellin also blocked the pro-myelinating effect of FTY720 (or fingolimod) on rOPC differentiation in vitro . Further, administration of FTY720 to wild-type C57BL/6 mice during MOG 35-55 -EAE ameliorated clinical disability while FTY720 administered to mice lacking expression of Timp1 in astrocytes ( Timp1 cKO ) had no effect. Analysis of human TIMP1 and fibronectin ( FN1 ) transcripts from healthy and multiple sclerosis (MS) patient brain samples revealed an inverse relationship where lower TIMP1 expression was coincident with elevated FN1 in MS astrocytes. Lastly, we analyzed proteomic databases of MS samples and identified anastellin peptides to be more abundant in the cerebrospinal fluid (CSF) of human MS patients with high versus low disease activity. The prospective role for anastellin generation in association with myelin lesions as a consequence of a lack of astrocytic TIMP-1 production could influence both the efficacy of fingolimod responses and the innate remyelination potential of the the MS brain.

Significance Statement

Astrocytic production of TIMP-1 prevents the protein catabolism of fibronectin. In the absence of TIMP-1, fibronectin is further digested leading to a higher abundance of anastellin peptides that can bind to sphingosine-1-phosphate receptor 1. The binding of anastellin with the sphingosine-1-phosphate receptor 1 impairs the differentiation of oligodendrocytes progenitor cells into myelinating oligodendrocytes in vitro , and negates the astrocyte-mediated therapeutic effects of FTY720 in the EAE model of chronic CNS inflammation. These data indicate that TIMP-1 production by astrocytes is important in coordinating astrocytic functions during inflammation. In the absence of astrocyte produced TIMP-1, elevated expression of anastellin may represent a prospective biomarker for FTY720 therapeutic responsiveness.

Complementary anti-cancer pathways triggered by inhibition of sideroflexin 4 in ovarian cancer

DNA damaging agents are a mainstay of standard chemotherapy for ovarian cancer. Unfortunately, resistance to such DNA damaging agents frequently develops, often due to increased activity of DNA repair pathways. Sideroflexin 4 (SFXN4) is a little-studied inner mitochondrial membrane protein. Here we demonstrate that SFXN4 plays a role in synthesis of iron sulfur clusters (Fe-S) in ovarian cancer cells and ovarian cancer tumor-initiating cells, and that knockdown of SFXN4 inhibits Fe-S biogenesis in ovarian cancer cells. We demonstrate that this has two important consequences that may be useful in anti-cancer therapy. First, inhibition of Fe-S biogenesis triggers the accumulation of excess iron, leading to oxidative stress. Second, because enzymes critical to multiple DNA repair pathways require Fe-S clusters for their function, DNA repair enzymes and DNA repair itself are inhibited by reduction of SFXN4. Through this dual mechanism, SFXN4 inhibition heightens ovarian cancer cell sensitivity to DNA-damaging drugs and DNA repair inhibitors used in ovarian cancer therapy, such as cisplatin and PARP inhibitors. Sensitization is achieved even in drug resistant ovarian cancer cells. Further, knockout of SFXN4 decreases DNA repair and profoundly inhibits tumor growth in a mouse model of ovarian cancer metastasis. Collectively, these results suggest that SFXN4 may represent a new target in ovarian cancer therapy.

Appearance of claudin-5+ leukocyte subtypes in the blood and CNS during progression of EAE

Background

Tight junctions (TJs) are membrane specializations characteristic of barrier-forming membranes, which function to seal the aqueous pathway between endothelial cells or epithelial cells and, thereby, obstruct intercellular solute and cellular movement. However, previous work from our laboratory found that claudin-5 (CLN-5), a TJ protein prominent at the blood–brain barrier (BBB), was also detected, ectopically, on leukocytes (CLN-5⁺) in the blood and central nervous system (CNS) of mice with experimental autoimmune encephalomyelitis (EAE), a neuroinflammatory, demyelinating disease that is a model for multiple sclerosis. CLN-5 was further shown to be transferred from endothelial cells to circulating leukocytes during disease, prompting consideration this action is coupled to leukocyte transendothelial migration (TEM) into the CNS by fostering transient interactions between corresponding leukocyte and endothelial junctional proteins at the BBB.

Methods

To begin clarifying the significance of CLN-5⁺ leukocytes, flow cytometry was used to determine their appearance in the blood and CNS during EAE.

Results

Flow cytometric analysis revealed CLN-5⁺ populations among CD4 and CD8 T cells, B cells, monocytes and neutrophils, and these appeared with varying kinetics and to different extents in both blood and CNS. CLN-5 levels on circulating T cells further correlated highly with activation state. And, the percentage of CLN-5⁺ cells among each of the subtypes analyzed was considerably higher in CNS tissue than in blood, consistent with the interpretation that CLN-5⁺ leukocytes gain preferred access to the CNS.

Conclusion

Several leukocyte subtypes variably acquire CLN-5 in blood before they enter the CNS, an event that may represent a novel mechanism to guide leukocytes to sites for paracellular diapedesis across the BBB.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02328-3.

The Hajdu Cheney Mutation Is a Determinant of B-Cell Allocation of the Splenic Marginal Zone

The neurogenic locus notch homolog protein (Notch)-2 receptor is a determinant of B-cell allocation, and gain-of-NOTCH2-function mutations are associated with Hajdu-Cheney syndrome (HCS), a disease presenting with osteoporosis and acro-osteolysis. We generated a mouse model reproducing the HCS mutation (Notch2HCS), and heterozygous global mutant mice displayed gain-of-Notch2 function. In the mutant spleen, the characteristic perifollicular rim marking the marginal zone (MZ), which is the interface between the nonlymphoid red pulp and the lymphoid white pulp, merged with components of the white pulp. As a consequence, the MZ of Notch2HCS mice occupied most of the splenic structure. To explore the mechanisms involved, lymphocyte populations from the bone marrow and spleen were harvested from heterozygous Notch2HCS mice and sex-matched control littermates and analyzed by flow cytometry. Notch2HCS mice had an increase in CD21/35^highCD23^- splenic MZ B cells of approximately fivefold and a proportional decrease in splenic follicular B cells (CD21/35^intCD23⁺) at 1, 2, and 12 months of age. Western blot analysis revealed that Notch2HCS mutant splenocytes had increased phospho-Akt and phospho-Jun N-terminal kinase, and gene expression analysis of splenic CD19⁺ B cells demonstrated induction of Hes1 and Hes5 in Notch2HCS mutants. Anti-Notch2 antibodies decreased MZ B cells in control and Notch2HCS mice. In conclusion, Notch2HCS mutant mice have increased mature B cells in the MZ of the spleen.

Age- and location-related changes in microglial function

Inflammation in the central nervous system (CNS) is primarily regulated by microglia. No longer considered a homogenous population, microglia display a high degree of heterogeneity, immunological diversity and regional variability in function. Given their low rate of self-renewal, the microenvironment in which microglia reside may play an important role in microglial senescence. This study examines age-related changes in microglia in the brain and spinal cord. Using ex-vivo flow cytometry analyses, functional assays were performed to assess changes in microglial morphology, oxidative stress, cytokine production, and phagocytic activity with age in both the brain and spinal cord. The regional CNS environment had a significant effect on microglial activity with age. Blood-CNS barrier permeability was greater in the aging spinal cord compared with aging brain; this was associated with increased tissue cytokine levels. Aged microglia had deficits in phagocytosis at baseline and after stimulus-induced activation. The identification of age-specific, high scatter microglia together with the use of ex-vivo functional analyses provides the first functional characterization of senescent microglia. Age and regional-specificity of CNS disease should be taken into consideration when developing immune-modulatory treatments.

Disrupted T cell central memory following vaccination in patients with sickle cell disease (P4536)

Increasing evidence suggests that a systemic state of disrupted immunity and inflammation accompanies sickle cell disease (SCD) despite the erythrocytic nature of the SCD mutation. Frequent infection plagues patients, who require aggressive vaccination from an early age. However, recent experimental and clinical evidence suggest diminished vaccine efficacy in SCD. We hypothesize that patients with SCD exhibit disrupted T cell memory in response to vaccination. We collected blood from nine healthy adult controls and eleven SCD patients before and 4-6 weeks after routine vaccination against influenza virus (IRB #11-026-1). Peripheral blood mononuclear cells were isolated and analyzed by flow cytometry. As previously reported, relative percentages of CD8+ central memory (CM) T cells significantly contracted following vaccination in control subjects (from 48.2 to 39.3, p < 0.01). Conversely, relative percentages of CD8+ CM T cells did not change in SCD patients (44.3 to 44.4, p > 0.05). Further, CD4+ CM T cells were significantly higher in patients with SCD versus controls before vaccination (58.7 vs. 44.7, p < 0.02) and trended higher following vaccination (56.8 vs. 40.7, p = 0.08). These data indicate that patients with SCD exhibit both disrupted CD8+ CM kinetics and altered CD4+ CM levels in the context of vaccination. Our findings suggest that at least a portion of the poor clinical response to vaccination in SCD may arise from disrupted T cell memory.

B cell exhaustion in sickle cell disease patients is associated with inhibited memory generation after influenza vaccination (P3009)

Dysregulated immunity is a hallmark of Sickle Cell Disease (SCD), and clinical evidence indicates that SCD patients mount adequate initial antigen-specific antibody responses only to have significant drops in titer levels 1-2 years post-vaccination. We thus hypothesized that SCD patients do not generate sufficient B-cell memory after vaccination. We conducted a translational study (IRB #11-026-1) using flow cytometric analysis of memory B-cells from frozen PBMCs taken from 11 SCD patients and 9 healthy controls before and 4-6 weeks after receiving the influenza vaccine. Percentages of CD19+ B-cells were similar between groups before vaccination, but only SCD patients showed a significant increase in B-cells after vaccination (P=0.04). However, control subjects generated approximately 2-fold more CD27+ memory B-cells after vaccination (P=0.03) while almost no change was observed in the SCD patients. This indicates that SCD patients generate naïve, but little to no memory B-cells after vaccination, thereby explaining the diminishing antibody titers observed by clinicians. Further analysis demonstrated that SCD patients have a significantly higher proportion of FcRL4+ exhausted B-cells at baseline when compared to controls (33% more; P=0.02). Given that FcRL4 down-regulates BCR signaling and is associated with reduced memory B-cell generation in people with chronic infections, we propose that chronic inflammation in SCD leads to B-cell exhaustion through BCR signal dampening.

Splenic morphological changes are accompanied by altered baseline immunity in a mouse model of sickle-cell disease

Although functional asplenia from infarctions may be a major contributor to increased infectious mortality in sickle-cell disease (SCD), this relationship has not been fully defined. We used the transgenic Berkeley SCD mouse to define blood and splenic immunophenotypic differences in this model compared with C57BL/6 and hemizygous controls. In the serum of SCD mice, we found increased IgG2a and suppressed IgM, IgG2b, and IgA levels. Serum IL-6 levels in SCD mice were elevated, whereas IL-1α, CXCL10, and CCL5 levels were decreased. The blood of SCD mice had higher white blood cell counts, with an increased percentage of lymphocytes and decreases in other leukocytes. Immunophenotyping of lymphocytes revealed higher percentages of CD8(+) and T-regulatory cells and lower percentages of B cells. SCD mouse spleens exhibited histological disorganization, with reduction of defined lymphoid follicles and expansion of red pulp, a greater than fourfold increase in splenic mononuclear cells, marked expansion of the nucleated red blood cell fraction, and B-cell and CD8(+) T-cell lymphopenia. Within the splenic B-cell population, there was a significant decrease in B-1a B cells, with a corresponding decrease in IgA secreting plasma cells in the gut. Confocal microscopy of spleens demonstrated complete disruption of the normal lymphofollicular structure in the white pulp of SCD mice without distinct B, T, and marginal zones. Our findings suggest that altered SCD splenic morphological characteristics result in an impaired systemic immune response.

Memory phenotype CD8 T cells generated in response to inducible self antigen (101.42)

Chronic antigenic stimulation of CD8 T cells by self antigen or chronic infection results in an altered CD8 T cell response and may lead to antigenic tolerance. To study these processes we generated transgenic mice in which antigen (Ag) expression is tightly controlled in DCs by doxycycline (dox). Our system provides the unique ability to examine endogenous CD8 T cell responses to neo-self Ag in the absence of overt inflammation. Dox can be given both chronically and acutely, and Ag expression ceases upon dox withdrawal. Importantly, the transgenic mice are ignorant of Ag prior to induction. Chronic antigen induction (dox on) in these mice resulted in a massive expansion of endogenous Ag-specific CD8 T cells. They upregulated CD44 and LFA-1, and expressed CD69 and PD1, but predominantly did not express KLRG1 or CD127, nor did they generate effector cytokines. Upon Ag removal (dox on, then dox off), the Ag-specific CD8 T cell population waned but the surviving population was enriched for CD127+ memory phenotype cells. The remaining CD8 T cells recalled to subsequent pathogen challenge but did not recall to self Ag challenge (dox back on). These studies indicate that chronic self Ag exposure generates a CD8 T cell population that is non functional, but persists through an addiction to Ag. However, when self Ag is removed, a functional memory phenotype CD8 T cell population emerges, which is regulated depending on the context of subsequent Ag presentation.

Generation of intestinal effector and memory CD8 T cells following oral Listeria monocytogenes infection (46.1)

The intestinal mucosa contains unique inductive and effector sites designed for antigen presentation and promotion of primary and memory CD8 T cell responses. Thus, generation of adaptive immunity within these tissues likely results in T cell responses with distinct cellular outcomes. Here, we utilized an oral Listeria monocytogenes (LM) infection model in which internalin A is modified to promote invasion of murine intestinal epithelial cells. Oral infection induced a robust CD8 T cell response. In peripheral nonmucosal tissues, the majority of LM-specific CD8 T cells resemble short-lived effector cells (SLEC; CD127- KLRG1+). Surprisingly, the majority of effector CD8 T cells in the intestinal mucosa resembled memory precursor effector cells (MPEC; CD127+ KLRG1-) following oral infection. Splenectomy failed to impact the mucosal or systemic T cell response suggesting an intestinal tissue as the major site of T cell priming. Of the inductive sites examined, only Peyer’s patch (PP) LM-specific CD8 T cells expressed CD69 and CD103. Moreover, expression of these receptors was maintained on memory CD8 T cells from the PP where they reside along the border of the T cell and B cell zones. Contrary to systemic recall via i.v. infection, oral recall resulted in preferential expansion of CD8 T cells expressing both CD127 and KLRG1. The maintenance of a stable memory population uniquely tailored to respond to intestinal pathogens may be a hallmark of oral challenge.

An inducible antigen system to study endogenous CD8 T cell tolerance (93.11)

Peripheral tolerance induction is critical for deterrence of autoimmunity. Most self-reactive T cells are developmentally deleted in the thymus. This deletion process is not absolute and self-reactive T cells can escape. These T cells must either be deleted or regulated in the periphery to prevent autoimmunity. To study these processes, we generated mice in which SIINFEKL expression can be tightly controlled in small intestinal epithelial cells or dendritic cells by administration of doxycycline. Our system provides the unique ability to examine endogenous T cell responses to tissue-specific and developmentally regulated self antigen. Importantly, the transgenic mice are ignorant of antigen prior to induction. Antigen induction in either the small intestine or dendritic cells caused tissue-specific activation of transferred TCR transgenic OT-I T cells. Antigen induction also resulted in activation and expansion of endogenous SIINFEKL-specific CD8 T cells that expressed PD1, but did not express KLRG1 or CD127. Antigen induction impaired a SIINFEKL-specific CD8 response to concomitant VSV OVA infection. However, in the absence of antigen induction, SIINFEKL-specific effector and memory CD8 T cell responses were generated, but the resultant memory CD8 T cells did not respond to subsequent self antigen induction. Characterization of immune responses in these antigen-inducible mice will provide key insights into mechanisms controlling tolerance versus autoimmunity.