The fetal liver (FL) is a prominent transient site for hematopoietic development in mammals. During hematopoietic ontogeny, immature HSCs migrate from primitive sites to the FL. The FL niche supports ...concomitant proliferation and maturation of nascent HSCs. The niche, composed of cells and regulatory factors, maintains the overall functionality of stem cells. Integrins, a class of adhesion receptors, located on HSC surface help transduce extrinsic signals from the niche, facilitating stem cell regulation. Itgav-b3, along with its ligand Postn, was shown to maintain HSC quiescence in the bone marrow (BM) (Khurana S. et al, 2016). RNA seq and flow cytometry data showed the presence of Itgav-b3 on FL HSCs as well. We questioned the role of Postn-Itgav axis in a site where HSC proliferation is the key feature. We found that disruption of Postn-Itgav axis in the FL led to further proliferation of FL HSCs. Interestingly, such proliferative events gave rise to functionally viable stem cells, unlike in the BM (Khurana S. et al, 2016). Further investigation showed that FL LSKs from induced proliferation culture as well as highly proliferative Postn-/- FL LSKs exhibited heightened DNA damage response (DDR), as opposed to wildtype. We propose that higher DDR might be the underlying reason for better tolerance of proliferative stress, thereby reflecting a developmental stage-dependent effect (Biswas A. et al, 2020). HSC proliferation in the FL gives rise to functionally potent stem cells, making the FL HSC niche a remarkable site for investigation. A composite understanding of the FL HSC microenvironment remains largely elusive. Following up on our studies on FL hematopoiesis, we made efforts to understand the composition of the HSC micro-niche within this tissue. Extensive 3D image analysis helped us draw a preliminary unbiased cellular architecture of the FL HSC niche.
Abstract
Epithelial, stromal, and immune cells in the skin cooperate to ensure appropriate response to pathogens and environmental damage. Recent single cell transcriptional analyses of healthy and ...fibrotic human skin revealed a wide range of phenotypes that arise in response to distinct cytokine milieu. Cutaneous T cells promote host defense and the subsequent resolution of inflammation and repair of damaged skin through the production of cytokines, but the precise mechanisms T cells use to impact the differentiation and function of skin cells involved in inflammatory and tissue-repair responses remain understudied. To assess the functional capacity of cutaneous lymphocytes we isolated skin-tropic and skin-resident T helper cells including a novel population of pro-fibrotic migratory tissue resident memory cells we recently discovered. We measured both quantitative T cell cytokine production following TCR stimulation, and the impact of T cell derived cytokines on human keratinocyte and fibroblast transcriptional profile and morphology. We find that phenotypically and functionally distinct circulating and skin-resident T cell subsets have the capacity to promote discrete cytokine-dependent transcriptional and cellular outcomes in the skin including the induction of metabolic, proliferative, and inflammatory gene profiles. Thus, cutaneous T cells support host-protective and tissue-repair responses through direct activity on keratinocytes and dermal fibroblasts.
Interaction of macrophages with apoptotic cells involves multiple steps including recognition, tethering, phagocytosis, and anti-inflammatory macrophage responses. Defective apoptotic cell clearance ...is associated with pathogenesis of autoimmune disease. CD14 is a surface receptor that functions in vitro in the removal of apoptotic cells by human and murine macrophages, but its mechanism of action has not been defined. Here, we demonstrate that CD14 functions as a macrophage tethering receptor for apoptotic cells. Significantly, CD14-/-macrophages in vivo are defective in clearing apoptotic cells in multiple tissues, suggesting a broad role for CD14 in the clearance process. However, the resultant persistence of apoptotic cells does not lead to inflammation or increased autoantibody production, most likely because, as we show, CD14-/-macrophages retain the ability to generate anti-inflammatory signals in response to apoptotic cells. We conclude that CD14 plays a broad tethering role in apoptotic cell clearance in vivo and that apoptotic cells can persist in the absence of proinflammatory consequences.
Abstract
Ultraviolet B (UVB) light is a common environmental trigger that can induce flares in several autoimmune diseases, but the mechanisms that mediate UVB-induced photosensitivity remain poorly ...understood. We used mice which express an autoimmune-driving isoform of Foxp3, called FoxP3 ΔE2mice, to develop a model autoimmune cutaneous photosensitivity. In the steady-state, FoxP3 ΔE2mice have high serum titers of IgE that target skin-associated autoantigens, and increased numbers of IL4-producing T follicular helper cells that target skin-associated proteins (Keratin 14) in the absence of overt immune challenge. After skin exposure to UVB light, FoxP3 ΔE2mice had further elevated IgE, worsened skin inflammation, and increased IgE complex deposition that localized to the challenge site. IgE production in UVB-challenged mice correlated with increased frequencies of germinal center (GC) B cells, elevated percentages of IL-4 +T follicular helper cells, and numbers of basophils with high surface expression of IgE in the draining lymph nodes of UVB-challenged skin. We also observed a significant increase in IgE accumulation, increased numbers of Tug8 +basophil extracellular traps in UVB-challenged skin and increased frequencies of activated plasmacytoid dendritic cells (CD80 +CD86 +) in the skin and skin-draining lymph nodes of FoxP3 ΔE2mice when compared to wild-type littermates. Collectively, we found that T follicular regulatory cells in FoxP3 ΔE2mice fail to maintain self-tolerance in the GC, resulting in increased production of skin reactive IgE and worsened skin inflammation driven by basophil extracellular trap accumulation in UVB-damaged skin.
Supported by grants from the NIH (F32 AI154787, R01 AI136475, R21 AI169418, and R21 AI152444)
Plasmacytoid dendritic cells (pDCs) are strongly implicated as a major source of IFN-I in systemic lupus erythematosus (SLE), triggered through TLR-mediated recognition of nucleic acids released from ...dying cells. However, relatively little is known about how TLR signaling and IFN-I production are regulated in pDCs. In this article, we describe a role for integrin αvβ3 in regulating TLR responses and IFN-I production by pDCs in mouse models. We show that αv and β3-knockout pDCs produce more IFN-I and inflammatory cytokines than controls when stimulated through TLR7 and TLR9 in vitro and in vivo. Increased cytokine production was associated with delayed acidification of endosomes containing TLR ligands, reduced LC3 conjugation, and increased TLR signaling. This dysregulated TLR signaling results in activation of B cells and promotes germinal center (GC) B cell and plasma cell expansion. Furthermore, in a mouse model of TLR7-driven lupus-like disease, deletion of αvβ3 from pDCs causes accelerated autoantibody production and pathology. We therefore identify a pDC-intrinsic role for αvβ3 in regulating TLR signaling and preventing activation of autoreactive B cells. Because αvβ3 serves as a receptor for apoptotic cells and cell debris, we hypothesize that this regulatory mechanism provides important contextual cues to pDCs and functions to limit responses to self-derived nucleic acids.
Severe acute pancreatitis (SAP) is associated with substantial morbidity and mortality. Several cytokines have been identified to have pathophysiological significance in SAP, but studies ...characterizing their early trajectories are lacking. Here we characterize the early trajectories of seven key cytokines associated with SAP and compare them with non-SAP subjects. Five proinflammatory cytokines (angiopoietin-2, interleukin-6, interleukin-8, monocyte chemoattractant protein-1, resistin) and two anti-inflammatory cytokines (hepatocyte growth factor, and soluble tumor necrosis factor-α receptor-1A) were measured in a prospective cohort of acute pancreatitis subjects (2012-2016) at the time of enrollment and then every 24 h for 5 days or until discharge. The cytokines' levels and trajectories were calibrated based on date of pain onset and were compared between healthy controls and three severity categories (mild, moderate, and severe). The cohort (
= 170) consisted of 27 healthy controls, 65 mild, 38 moderate, and 40 SAP. From
of symptom onset, SAP subjects exhibited significantly higher levels of both pro- and anti-inflammatory cytokines compared with non-SAP and healthy subjects. But in SAP subjects, all proinflammatory cytokines' levels trended downward after
(except for a flat slope for angiopoeitin-2) whereas for non-SAP subjects, the trajectory was upward: this trajectory difference between SAP versus non-SAP subjects resulted in narrowing of the differences initially seen on
for proinflammatory cytokines. For anti-inflammatory cytokines, the trajectories were uniformly upward for both SAP and non-SAP subjects. Proinflammatory cytokine response is an early and time-sensitive event in SAP that should be accounted for when designing future biomarker studies and/or therapeutic trials.
In this study, we showed that the proinflammatory cytokine response in SAP is an early event, with subsequent downregulation of proinflammatory cytokines beginning at
of symptom onset. Our findings underscore the importance of enrolling subjects very early in the disease course when conducting studies to investigate early immune events of SAP; this current study also serves as an important reference for the design of future biomarker studies and therapeutic trials in SAP.
Atherosclerotic plaque formation is fueled by the persistence of lipid-laden macrophages in the artery wall. The mechanisms by which these cells become trapped, thereby establishing chronic ...inflammation, remain unknown. Here we found that netrin-1, a neuroimmune guidance cue, was secreted by macrophages in human and mouse atheroma, where it inactivated the migration of macrophages toward chemokines linked to their egress from plaques. Acting via its receptor, UNC5b, netrin-1 inhibited the migration of macrophages directed by the chemokines CCL2 and CCL19, activation of the actin-remodeling GTPase Rac1 and actin polymerization. Targeted deletion of netrin-1 in macrophages resulted in much less atherosclerosis in mice deficient in the receptor for low-density lipoprotein and promoted the emigration of macrophages from plaques. Thus, netrin-1 promoted atherosclerosis by retaining macrophages in the artery wall. Our results establish a causative role for negative regulators of leukocyte migration in chronic inflammation.
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