Pathogen-associated molecular patterns (PAMPs) trigger host immune response by activating pattern recognition receptors like toll-like receptors (TLRs). However, the mechanism whereby several ...pathogens, including viruses, activate TLRs via a non-PAMP mechanism is unclear. Endogenous "inflammatory mediators" called damage-associated molecular patterns (DAMPs) have been implicated in regulating immune response and inflammation. However, the role of DAMPs in inflammation/immunity during virus infection has not been studied. We have identified a DAMP molecule, S100A9 (also known as Calgranulin B or MRP-14), as an endogenous non-PAMP activator of TLR signaling during influenza A virus (IAV) infection. S100A9 was released from undamaged IAV-infected cells and extracellular S100A9 acted as a critical host-derived molecular pattern to regulate inflammatory response outcome and disease during infection by exaggerating pro-inflammatory response, cell-death and virus pathogenesis. Genetic studies showed that the DDX21-TRIF signaling pathway is required for S100A9 gene expression/production during infection. Furthermore, the inflammatory activity of extracellular S100A9 was mediated by activation of the TLR4-MyD88 pathway. Our studies have thus, underscored the role of a DAMP molecule (i.e. extracellular S100A9) in regulating virus-associated inflammation and uncovered a previously unknown function of the DDX21-TRIF-S100A9-TLR4-MyD88 signaling network in regulating inflammation during infection.
The transition from acute to chronic pain is critically important but not well understood. Here, we investigated the pathophysiological mechanisms underlying the transition from acute to chronic low ...back pain (LBP) and performed transcriptome-wide analysis in peripheral immune cells of 98 participants with acute LBP, followed for 3 months. Transcriptomic changes were compared between patients whose LBP was resolved at 3 months with those whose LBP persisted. We found thousands of dynamic transcriptional changes over 3 months in LBP participants with resolved pain but none in those with persistent pain. Transient neutrophil-driven up-regulation of inflammatory responses was protective against the transition to chronic pain. In mouse pain assays, early treatment with a steroid or nonsteroidal anti-inflammatory drug (NSAID) also led to prolonged pain despite being analgesic in the short term; such a prolongation was not observed with other analgesics. Depletion of neutrophils delayed resolution of pain in mice, whereas peripheral injection of neutrophils themselves, or S100A8/A9 proteins normally released by neutrophils, prevented the development of long-lasting pain induced by an anti-inflammatory drug. Analysis of pain trajectories of human subjects reporting acute back pain in the UK Biobank identified elevated risk of pain persistence for subjects taking NSAIDs. Thus, despite analgesic efficacy at early time points, the management of acute inflammation may be counterproductive for long-term outcomes of LBP sufferers.
The S100A9 and S100A8 proteins are highly expressed by neutrophils and monocytes and are part of a group of damage-associated molecular pattern molecules that trigger inflammatory responses. Sera and ...synovial fluids of patients with rheumatoid arthritis (RA) contain high concentrations of S100A8/A9 that correlate with disease activity.
In this study, we investigated the importance of S100A9 in RA by using neutralizing antibodies in a murine lipopolysaccharide-synchronized collagen-induced arthritis model. We also used an in vitro model of stimulation of human immune cells to decipher the role played by S100A9 in leukocyte migration and pro-inflammatory cytokine secretion.
Treatment with anti-S100A9 antibodies improved the clinical score by 50%, diminished immune cell infiltration, reduced inflammatory cytokines, both in serum and in the joints, and preserved bone/collagen integrity. Stimulation of neutrophils with S100A9 protein led to the enhancement of neutrophil transendothelial migration. S100A9 protein also induced the secretion by monocytes of proinflammatory cytokines like TNFα, IL-1β and IL-6, and of chemokines like MIP-1α and MCP-1.
The effects of anti-S100A9 treatment are likely direct consequences of inhibiting the S100A9-mediated promotion of neutrophil transmigration and secretion of pro-inflammatory cytokines from monocytes. Collectively, our results show that treatment with anti-S100A9 may inhibit amplification of the immune response and help preserve tissue integrity. Therefore, S100A9 is a promising potential therapeutic target for inflammatory diseases like rheumatoid arthritis for which alternative therapeutic strategies are needed.
The study of S100A9 in viral infections has seen increased interest since the COVID-19 pandemic. S100A8/A9 levels were found to be correlated with the severity of COVID-19 disease, cytokine storm, ...and changes in myeloid cell subsets. These data led to the hypothesis that S100A8/A9 proteins might play an active role in COVID-19 pathogenesis. This review explores the structures and functions of S100A8/9 and the current knowledge on the involvement of S100A8/A9 and its constituents in viral infections. The potential roles of S100A9 in SARS-CoV-2 infections are also discussed.
S100A9 induces degranulation in human neutrophils.
S100A9 is a proinflammatory protein, expressed abundantly in the cytosol of neutrophils and monocytes. High extracellular S100A9 concentrations have ...been correlated with chronic inflammatory diseases such as rheumatoid arthritis and Crohn's disease, as well as with phagocyte extravasation. This study tested the hypothesis that S100A9 induces degranulation in human neutrophils. S100A9 was found to up‐regulate the surface expression of CD35 and CD66b, proteins contained in secretory vesicles and specific/gelatinase granules, respectively. In addition, gelatinase and albumin, stored, respectively, in specific/gelatinase granules and secretory vesicles, were detected in the supernatants of neutrophils stimulated with S100A9. In contrast, stimulation with S100A9 had no effect on CD63 expression or MPO secretion, two proteins contained in azurophilic granules. S100A9 induced the phosphorylation of the MAPKs, ERK1/2, p38, and JNK. Inhibition of p38 and JNK but not ERK1/2, with specific inhibitors (SB203580, JNKII, and PD98059, respectively), blocked neutrophil degranulation induced by S100A9. Taken together, these results support the hypothesis and clearly indicate that S100A9 induces the degranulation of secretory and specific/gelatinase granules but not of azurophilic granules in a process involving p38 and JNK and further support its classification as a DAMP.
S100A8 and S100A9 are cytoplasmic proteins expressed by phagocytes. High concentrations of these proteins have been correlated with various inflammatory conditions, including autoimmune diseases such ...as rheumatoid arthritis and Crohn's disease, as well as autoinflammatory diseases. In the present study, we examined the effects of S100A8 and S100A9 on the secretion of cytokines and chemokines from PBMCs. S100A8 and S100A9 induced the secretion of cytokines such as IL-6, IL-8, and IL-1β. This secretion was associated with the activation and translocation of the transcription factor NF-κB. Inhibition studies using antisense RNA and the pharmacological agent BAY-117082 confirmed the involvement of NF-κB in IL-6, IL-8, and IL-1β secretion. S100A8- and S100A9-mediated activation of NF-κB, the NLR family, pyrin domain-containing 3 (NLRP3) protein, and pro-IL-1β expression was dependent on the generation of reactive oxygen species. This effect was synergistically enhanced by ATP, a known inflammasome activator. These results suggest that S100A8 and S100A9 enhance the inflammatory response by inducing cytokine secretion of PBMCs.
S100A8 and S100A9 are small calcium-binding proteins that are highly expressed in neutrophil and monocyte cytosol and are found at high levels in the extracellular milieu during inflammatory ...conditions. Although reports have proposed a proinflammatory role for these proteins, their extracellular activity remains controversial. In this study, we report that S100A8, S100A9, and S100A8/A9 caused neutrophil chemotaxis at concentrations of 10(-12)-10(-9) M. S100A8, S100A9, and S100A8/A9 stimulated shedding of L-selectin, up-regulated and activated Mac-1, and induced neutrophil adhesion to fibrinogen in vitro. Neutralization with Ab showed that this adhesion was mediated by Mac-1. Neutrophil adhesion was also associated with an increase in intracellular calcium levels. However, neutrophil activation by S100A8, S100A9, and S100A8/A9 did not induce actin polymerization. Finally, injection of S100A8, S100A9, or S100A8/A9 into a murine air pouch model led to rapid, transient accumulation of neutrophils confirming their activities in vivo. These studies 1) show that S100A8, S100A9, and S100A8/A9 are potent stimulators of neutrophils and 2) strongly suggest that these proteins are involved in neutrophil migration to inflammatory sites.
S100A8 and S100A9 are calcium-binding proteins predominantly expressed by neutrophils and monocytes and play key roles in both normal and pathological inflammation. Recently, both proteins were found ...to promote tumor progression through the establishment of premetastatic niches and inhibit antitumor immune responses. Although S100A8 and S100A9 have been studied in solid cancers, their functions in hematological malignancies remain poorly understood. However, S100A8 and S100A9 are highly expressed in acute myeloid leukemia (AML), and S100A8 expression has been linked to poor prognosis in AML. We identified a small subpopulation of cells expressing S100A8 and S100A9 in AML mouse models and primary human AML samples. In vitro and in vivo analyses revealed that S100A9 induces AML cell differentiation, whereas S100A8 prevents differentiation induced by S100A9 activity and maintains AML immature phenotype. Treatment with recombinant S100A9 proteins increased AML cell maturation, induced growth arrest, and prolonged survival in an AML mouse model. Interestingly, anti-S100A8 antibody treatment had effects similar to those of S100A9 therapy in vivo, suggesting that high ratios of S100A9 over S100A8 are required to induce differentiation. Our in vitro studies on the mechanisms/pathways involved in leukemic cell differentiation revealed that binding of S100A9 to Toll-like receptor 4 (TLR4) promotes activation of p38 mitogen-activated protein kinase, extracellular signal-regulated kinases 1 and 2, and Jun N-terminal kinase signaling pathways, leading to myelomonocytic and monocytic AML cell differentiation. These findings indicate that S100A8 and S100A9 are regulators of myeloid differentiation in leukemia and have therapeutic potential in myelomonocytic and monocytic AMLs.
•S100A9 induces differentiation and growth arrest of AML cells via TLR4.•S100A8 regulates S100A9 activity and sustains AML immature phenotype.
High concentrations of the damage-associated molecular patterns S100A8 and S100A9 are found in skin and serum from patients suffering from psoriasis, an IL-17-related disease. Notably, although the ...expression of these proteins correlates with psoriatic disease severity, the exact function of S100A8 and S100A9 in psoriasis pathogenesis remains unclear. In this study, we investigated the role of S100A8 and S100A9 in psoriasis-associated skin hyperplasia and immune responses using
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mice in an imiquimod-induced model of psoriasis. We found that
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psoriatic mice exhibit worsened clinical symptoms relative to wild-type mice and increased expression of S100A9 and S100A8 proteins in keratinocytes, respectively. In addition, the loss of S100A8 enhances proliferation of keratinocytes and disrupts keratinocyte differentiation. We further detected elevated production of IL-17A and -F from CD4
T cells in the absence of S100A8 and S100A9, as well as increased infiltration of neutrophils in the skin. In addition, treatment with anti-IL-17A and -F was found to reduce psoriasis symptoms and skin hyperplasia in
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mice. These data suggest that S100A8 and S100A9 regulate psoriasis by inhibiting production of IL-17A and -F, thereby, to our knowledge, providing new insights into their biological functions.
Neutrophils are the most abundant leukocytes in humans and play a role in the innate immune response by being the first cells attracted to the site of infection. While early studies presented ...neutrophils as almost exclusively glycolytic cells, recent advances show that these cells use several metabolic pathways other than glycolysis, such as the pentose phosphate pathway, oxidative phosphorylation, fatty acid oxidation, and glutaminolysis, which they modulate to perform their functions. Metabolism shifts from fatty acid oxidation-mediated mitochondrial respiration in immature neutrophils to glycolysis in mature neutrophils. Tissue environments largely influence neutrophil metabolism according to nutrient sources, inflammatory mediators, and oxygen availability. Inhibition of metabolic pathways in neutrophils results in impairment of certain effector functions, such as NETosis, chemotaxis, degranulation, and reactive oxygen species generation. Alteration of these neutrophil functions is implicated in certain human diseases, such as antiphospholipid syndrome, coronavirus disease 2019, and bronchiectasis. Metabolic regulators such as AMPK, HIF-1α, mTOR, and Arf6 are linked to neutrophil metabolism and function and could potentially be targeted for the treatment of diseases associated with neutrophil dysfunction. This review details the effects of alterations in neutrophil metabolism on the effector functions of these cells.
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