IL-6 blocks a discrete early step in lymphopoiesis

SARS-CoV-2-associated lymphopenia: possible mechanisms and the role of CD147

T lymphocytes play a primary role in the adaptive antiviral immunity. Both lymphocytosis and lymphopenia were found to be associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While lymphocytosis indicates an active anti-viral response, lymphopenia is a sign of poor prognosis. T-cells, in essence, rarely express ACE2 receptors, making the cause of cell depletion enigmatic. Moreover, emerging strains posed an immunological challenge, potentially alarming for the next pandemic. Herein, we review how possible indirect and direct key mechanisms could contribute to SARS-CoV-2-associated-lymphopenia. The fundamental mechanism is the inflammatory cytokine storm elicited by viral infection, which alters the host cell metabolism into a more acidic state. This "hyperlactic acidemia" together with the cytokine storm suppresses T-cell proliferation and triggers intrinsic/extrinsic apoptosis. SARS-CoV-2 infection also results in a shift from steady-state hematopoiesis to stress hematopoiesis. Even with low ACE2 expression, the presence of cholesterol-rich lipid rafts on activated T-cells may enhance viral entry and syncytia formation. Finally, direct viral infection of lymphocytes may indicate the participation of other receptors or auxiliary proteins on T-cells, that can work alone or in concert with other mechanisms. Therefore, we address the role of CD147-a novel route-for SARS-CoV-2 and its new variants. CD147 is not only expressed on T-cells, but it also interacts with other co-partners to orchestrate various biological processes. Given these features, CD147 is an appealing candidate for viral pathogenicity. Understanding the molecular and cellular mechanisms behind SARS-CoV-2-associated-lymphopenia will aid in the discovery of potential therapeutic targets to improve the resilience of our immune system against this rapidly evolving virus.

Anti-viral effect of usenamine a using SARS-CoV-2 pseudo-typed viruses

The escalating pandemic brought about by the novel SARS-CoV-2 virus is threatening global health, and thus, it is necessary to develop effective antiviral drugs. Usenamine A is a dibenzo-furan derivative separated from lichen Usnea diffracta showing broad-spectrum activity against different viruses. We evaluate that usenamine A has antiviral effects against novel SARS-CoV-2 Delta variant pseudotyped viruses (PVs) in A549 cells. In addition, usenamine A significantly suppresses SARS-CoV-2 PV-induced mitochondrial depolarization, elevated reactive oxygen species (ROS) levels, apoptosis, and inflammation. Usenamine A also causes the SARS-CoV-2 spike protein to become less stable. Thus, usenamine A shows potential as an antiviral drug that can provide protection against COVID-19.

Microbiota Influences on Hematopoiesis and Blood Cancers: New Horizons?

Hematopoiesis governs the generation of immune cells through the differentiation of hematopoietic stem cells (HSC) into various progenitor cells, a process controlled by intrinsic and extrinsic factors. Among extrinsic factors influencing hematopoiesis is the microbiota, or the collection of microorganisms present in various body sites. The microbiota has a profound impact on host homeostasis by virtue of its ability to release various molecules and structural components, which promote normal organ function. In this review, we will discuss the role of microbiota in influencing hematopoiesis and how disrupting the microbiota/host network could lead to hematologic malignancies, as well as highlight important knowledge gaps to move this field of research forward.

SIGNIFICANCE

Microbiota dysfunction is associated with many pathologic conditions, including hematologic malignancies. In this review, we discuss the role of microbiota in influencing hematopoiesis and how disrupting the microbiota/host network could lead to hematologic malignancies. Understanding how the microbiota influences hematologic malignancies could have an important therapeutic impact for patients.

Zymosan Particle-Induced Hemodynamic, Cytokine and Blood Cell Changes in Pigs: An Innate Immune Stimulation Model with Relevance to Cytokine Storm Syndrome and Severe COVID-19

Hemodynamic disturbance, a rise in neutrophil-to-lymphocyte ratio (NLR) and release of inflammatory cytokines into blood, is a bad prognostic indicator in severe COVID-19 and other diseases involving cytokine storm syndrome (CSS). The purpose of this study was to explore if zymosan, a known stimulator of the innate immune system, could reproduce these changes in pigs. Pigs were instrumented for hemodynamic analysis and, after i.v. administration of zymosan, serial blood samples were taken to measure blood cell changes, cytokine gene transcription in PBMC and blood levels of inflammatory cytokines, using qPCR and ELISA. Zymosan bolus (0.1 mg/kg) elicited transient hemodynamic disturbance within minutes without detectable cytokine or blood cell changes. In contrast, infusion of 1 mg/kg zymosan triggered maximal pulmonary hypertension with tachycardia, lasting for 30 min. This was followed by a transient granulopenia and then, up to 6 h, major granulocytosis, resulting in a 3-4-fold increase in NLR. These changes were paralleled by massive transcription and/or rise in IL-6, TNF-alpha, CCL-2, CXCL-10, and IL-1RA in blood. There was significant correlation between lymphopenia and IL-6 gene expression. We conclude that the presented model may enable mechanistic studies on late-stage COVID-19 and CSS, as well as streamlined drug testing against these conditions.

Biomarkers of sequela in adult patients convalescing from COVID-19

Different biomarkers for SARS-CoV-2 have been linked to detection, diagnosis, treatment, disease progression, and development of new drugs and vaccines. The objective of this research was to evaluate various hematological, biochemicals, immunological, radiological and spirometric parameters in 20 adult patients convalescing from COVID-19 and their possible relationship with the clinical course of the disease. The frequencies of categorical variables were compared using the chi-square and Fisher's exact test. The levels of statistical significance were denoted in each figure legend. Two-dimensional clustering analysis was performed using MeV software from TIGR. The tests with P value of ≤ 0.05 were considered statistically significant. Most of the patients studied presented alterations in dissimilar laboratory, radiological and spirometric parameters, which were related to the clinical evolution of the disease. The results obtained show that certain hematological, biochemical, immunological and radiological parameters can be considered as biomarkers of sequela in adult COVID-19 patients, which allows their stratification, according to the degree of involvement or sequela, into three groups: I (mild degree of involvement or sequela), without lung lesions on computerized axial tomography (CT scan) and high values of IgG, C3 and hemoglobin, II (moderate degree of involvement or sequel), without lung lesions on CT scan, characterized by high levels of CD3+/CD4+ T lymphocytes and the rest of the variables with low values and III (severe degree of involvement or sequela), with lung lesions on CT scan and high values of erythrocyte sedimentation rate, monocytes and neutrophils, associated with lymphopenia and decreased concentrations of IgG and C3.

Chronic inflammation decreases HSC fitness by activating the druggable Jak/Stat3 signaling pathway

Chronic inflammation represents a major threat to human health since long-term systemic inflammation is known to affect distinct tissues and organs. Recently, solid evidence demonstrated that chronic inflammation affects hematopoiesis; however, how chronic inflammation affects hematopoietic stem cells (HSCs) on the mechanistic level is poorly understood. Here, we employ a mouse model of chronic multifocal osteomyelitis (CMO) to assess the effects of a spontaneously developed inflammatory condition on HSCs. We demonstrate that hematopoietic and nonhematopoietic compartments in CMO BM contribute to HSC expansion and impair their function. Remarkably, our results suggest that the typical features of murine multifocal osteomyelitis and the HSC phenotype are mechanistically decoupled. We show that the CMO environment imprints a myeloid gene signature and imposes a pro-inflammatory profile on HSCs. We identify IL-6 and the Jak/Stat3 signaling pathway as critical mediators. However, while IL-6 and Stat3 blockage reduce HSC numbers in CMO mice, only inhibition of Stat3 activity significantly rescues their fitness. Our data emphasize the detrimental effects of chronic inflammation on stem cell function, opening new venues for treatment.

Sarcoidosis and COVID-19: At the Cross-Road between Immunopathology and Clinical Manifestation

Coronavirus disease 2019 (COVID-19) has been associated with dysregulation of the immune system featuring inappropriate immune responses, exacerbation of inflammatory responses, and multiple organ dysfunction syndrome in patients with severe disease. Sarcoidosis, also known as Besnier-Boeck-Schaumann disease, is an idiopathic granulomatous multisystem disease characterized by dense epithelioid non-necrotizing lesions with varying degrees of lymphocytic inflammation. These two diseases have similar clinical manifestations and may influence each other at multiple levels, eventually affecting their clinical courses and prognosis. Notably, sarcoidosis patients are at high risk of severe COVID-19 pneumonia because of the underlying lung disease and chronic immunosuppressive treatment. In this narrative review, we will discuss interactions between sarcoidosis and COVID-19 in terms of clinical manifestations, treatment, and pathogenesis, including the role of the dysregulated renin-angiotensin system, altered immune responses involving increased cytokine levels and immune system hyperactivation, and cellular death pathways.

Inflammatory and blood gas markers of COVID-19 delirium compared to non-COVID-19 delirium: a cross-sectional study

OBJECTIVES

We aimed to find the association of inflammation and respiratory failure with delirium in COVID-19 patients. We compare the inflammatory and arterial blood gas markers between patients with COVID-19 delirium and delirium in other medical disorders.

METHODS

This cross-sectional study used the CHART-DEL, a validated research tool, to screen patients for delirium retrospectively from clinical notes. Inflammatory markers C-reactive protein (CRP) and white cell count (WBC), and the partial pressures of oxygen (PO₂) and carbon dioxide (PCO₂) were compared between patients with COVID-19 delirium and delirium in other medical disorders.

RESULTS

In bivariate analysis, CRP (mg/L) was significantly higher in the COVID-19 group, (81.7 ± 80.0 vs. 58.8 ± 87.7, p = 0.04), and WBC (10⁹/L) was significantly lower (7.44 ± 3.42 vs. 9.71 ± 5.45, p = 0.04). The geometric mean of CRP in the COVID-19 group was 140% higher in multiple linear regression (95% CI = 7-439%, p = 0.03) with age and sex as covariates. There were no significant differences in pO₂ or pCO₂ across groups.

CONCLUSION

The association between higher CRP and COVID-19 in patients with delirium may suggest an inflammatory basis for delirium in COVID-19. Our findings may assist clinicians in establishing whether delirium is due to COVID-19, which may improve management and outcomes of infected patients.

IL-6 drives T cell death to participate in lymphopenia in COVID-19

Lymphopenia is a common observation in patients with COVID-19. To explore the cause of T cell lymphopenia in the disease, laboratory results of 64 hospitalized COVID-19 patients were retrospectively analyzed and six patients were randomly selected to trace their changes of T lymphocytes and plasma concentration of IL-6 for the course of disease. Results confirmed that the T-cell lymphopenia, especially CD4⁺ T cell reduction in COVID-19 patients, was a reliable indicator of severity and hospitalization in infected patients. And CD4⁺ T cell count below 200 cells/μL predicts critical illness in COVID-19 patients. In vitro assay supported that exposure to key contributors (IL-1β, IL-6, TNF-α and IFN-γ) of COVID-19 cytokine storm caused substantial death of activated T cells. Among these contributors, IL-6 level was found to probably reversely correlate with T cell counts in patients. And IL-6 alone was potent to induce T cell reduction by gasderminE-mediated pyroptosis, inferring IL-6 took a part in affecting the function and status of T cells in COVID-19 patients. Intervention of IL-6 mediated T cell pryprotosis may effectively delay disease progression, maintain normal immune status at an early stage of infection.

The cytokine network in acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly heterogeneous malignancy of the blood and bone marrow, characterized by clonal expansion of myeloid stem and progenitor cells and rapid disease progression. Chemotherapy has been the first-line treatment for AML for more than 30 years. Application of recent high-throughput next-generation sequencing technologies has revealed significant molecular heterogeneity to AML, which in turn has motivated efforts to develop new, targeted therapies. However, due to the high complexity of this disease, including multiple driver mutations and the coexistence of multiple competing tumorigenic clones, the successful incorporation of these new agents into clinical practice remains challenging. These continuing difficulties call for the identification of innovative therapeutic approaches that are effective for a larger cohort of AML patients. Recent studies suggest that chronic immune stimulation and aberrant cytokine signaling act as triggers for AML initiation and progression, facets of the disease which might be exploited as promising targets in AML treatment. However, despite the greater appreciation of cytokine profiles in AML, the exact functions of cytokines in AML pathogenesis are not fully understood. Therefore, unravelling the molecular basis of the complex cytokine networks in AML is a prerequisite to develop new therapeutic alternatives based on targeting cytokines and their receptors.

COVID-19 and the potential of Janus family kinase (JAK) pathway inhibition: A novel treatment strategy

Recent evidence proposed that the severity of the coronavirus disease 2019 (COVID-19) in patients is a consequence of cytokine storm, characterized by increased IL-1β, IL-6, IL-18, TNF-α, and IFN-γ. Hence, managing the cytokine storm by drugs has been suggested for the treatment of patients with severe COVID-19. Several of the proinflammatory cytokines involved in the pathogenesis of COVID-19 infection recruit a distinct intracellular signaling pathway mediated by JAKs. Consequently, JAK inhibitors, including baricitinib, pacritinib, ruxolitinib, and tofacitinib, may represent an effective therapeutic strategy for controlling the JAK to treat COVID-19. This study indicates the mechanism of cytokine storm and JAK/STAT pathway in COVID-19 as well as the medications used for JAK/STAT inhibitors.

Analysis of hematological parameters in rheumatoid arthritis patients receiving biological therapy: contribution to prevention of avoidable hematological complications

Administration of biological therapy (BT) in rheumatoid arthritis (RA) patients is often associated with hematological complications, which result in switching among therapies. Thus, there is an instant need for suitable screening parameters that will help to individualize the therapy and minimize the onset of adverse effects. We analyzed the hematological profile of 99 RA patients receiving TNFα (Adalimumab - ADA, Golimumab - GOL, Etanercept - ETA) or IL-6 receptor (Tocilizumab - TCZ) inhibitors in order to find possible indicators to improve personalization of RA therapy. BTs significantly affect the levels of observed hematological parameters. In contrast to TNF-α inhibitors, TCZ normalized almost all monitored hematological parameters to values of healthy donors. Only GOL from the TNF-α inhibitors studied, was able to normalize neutrophil counts, as well as platelet indicators. Importantly, effects on the blood parameters (e.g. lymphocytes or platelet count) differ even within the same therapeutic group (anti-TNFα). Variable effects of individual biological agents in RA treatment point to importance to evaluate the patient's hematological profile to improve the selection of suitable BT. It will help to personalize the administration of BT and prevent unnecessary switching from an effective therapy just because of provocation of avoidable hematological complications.

T helper type (Th1/Th2) responses to SARS-CoV-2 and influenza A (H1N1) virus: From cytokines produced to immune responses

Cytokines produced by T helper cells (Th cells) have essential roles in the body's defense against viruses. Type 1 T helper (Th1) cells are essential for the host defense toward intracellular pathogens while T helper type 2 (Th2) cells are considered to be critical for the helminthic parasites' elimination swine-origin influenza A (H1N1) virus, a disease led to an epidemic in 2009 and rapidly spread globally via human-to-human transmission. Coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused a global pandemic in 2020 and is a serious threat to the public health. Pulmonary immunopathology is the leading cause of death during influenza and SARS-CoV-2 epidemics and pandemics. Influenza and SARS-CoV-2 cause high levels of cytokines in the lung. Both inadequate levels and high levels of specific cytokines can have side effects. In this literature review article, we want to compare the Th1 and Th2 cells responses in SARS-CoV-2 and H1N1.

Triple jeopardy in ageing: COVID-19, co-morbidities and inflamm-ageing

Covid-19 endangers lives, has disrupted normal life, changed the way medicine is practised and is likely to alter our world for the foreseeable future. Almost two years on since the presumptive first diagnosis of COVID-19 in China, more than two hundred and fifty million cases have been confirmed and more than five million people have died globally, with the figures rising daily. One of the most striking aspects of COVID-19 illness is the marked difference in individuals' experiences of the disease. Some, most often younger groups, are asymptomatic, whereas others become severely ill with acute respiratory distress syndrome (ARDS), pneumonia or proceed to fatal organ disease. The highest death rates are in the older and oldest age groups and in people with co-morbidities such as diabetes, heart disease and obesity. Three major questions seem important to consider. What do we understand about changes in the immune system that might contribute to the older person's risk of developing severe COVID-19? What factors contribute to the higher morbidity and mortality in older people with COVID-19? How could immunocompetence in the older and the frailest individuals and populations be supported and enhanced to give protection from serious COVID-19 illness?

Neutrophil Homeostasis and Emergency Granulopoiesis: The Example of Systemic Juvenile Idiopathic Arthritis

Neutrophils are key pathogen exterminators of the innate immune system endowed with oxidative and non-oxidative defense mechanisms. More recently, a more complex role for neutrophils as decision shaping cells that instruct other leukocytes to fine-tune innate and adaptive immune responses has come into view. Under homeostatic conditions, neutrophils are short-lived cells that are continuously released from the bone marrow. Their development starts with undifferentiated hematopoietic stem cells that pass through different immature subtypes to eventually become fully equipped, mature neutrophils capable of launching fast and robust immune responses. During severe (systemic) inflammation, there is an increased need for neutrophils. The hematopoietic system rapidly adapts to this increased demand by switching from steady-state blood cell production to emergency granulopoiesis. During emergency granulopoiesis, the de novo production of neutrophils by the bone marrow and at extramedullary sites is augmented, while additional mature neutrophils are rapidly released from the marginated pools. Although neutrophils are indispensable for host protection against microorganisms, excessive activation causes tissue damage in neutrophil-rich diseases. Therefore, tight regulation of neutrophil homeostasis is imperative. In this review, we discuss the kinetics of neutrophil ontogenesis in homeostatic conditions and during emergency myelopoiesis and provide an overview of the different molecular players involved in this regulation. We substantiate this review with the example of an autoinflammatory disease, i.e. systemic juvenile idiopathic arthritis.

COVID-19, what could sepsis, severe acute pancreatitis, gender differences, and aging teach us?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a potentially life-threatening disease, defined as Coronavirus Disease 19 (COVID-19). The most common signs and symptoms of this pathological condition include cough, fever, shortness of breath, and sudden onset of anosmia, ageusia, or dysgeusia. The course of COVID-19 is mild or moderate in more than 80% of cases, but it is severe or critical in about 14% and 5% of infected subjects respectively, with a significant risk of mortality. SARS-CoV-2 related infection is characterized by some pathogenetic events, resembling those detectable in other pathological conditions, such as sepsis and severe acute pancreatitis. All these syndromes are characterized by some similar features, including the coexistence of an exuberant inflammatory- as well as an anti-inflammatory-response with immune depression. Based on current knowledge concerning the onset and the development of acute pancreatitis and sepsis, we have considered these syndromes as a very interesting paradigm for improving our understanding of pathogenetic events detectable in patients with COVID-19. The aim of our review is: 1)to examine the pathogenetic mechanisms acting during the emergence of inflammatory and anti-inflammatory processes in human pathology; 2)to examine inflammatory and anti-inflammatory events in sepsis, acute pancreatitis, and SARS-CoV-2 infection and clinical manifestations detectable in patients suffering from these syndromes also according to the age and gender of these individuals; as well as to analyze the possible common and different features among these pathological conditions; 3)to obtain insights into our knowledge concerning COVID-19 pathogenesis. This approach may improve the management of patients suffering from this disease and it may suggest more effective diagnostic approaches and schedules of therapy, depending on the different phases and/or on the severity of SARS-CoV-2 infection.

MicroRNAs and JAK/STAT3 signaling: A new promising therapeutic axis in blood cancers

Blood disorders include a wide spectrum of blood-associated malignancies resulting from inherited or acquired defects. The ineffectiveness of existing therapies against blood disorders arises from different reasons, one of which is drug resistance, so different types of leukemia may show different responses to treatment. Leukemia occurs for a variety of genetic and acquired reasons, leading to uncontrolled proliferation in one or more cell lines. Regarding the genetic defects, oncogene signal transducer and activator of transcription (STAT) family transcription factor, especially STAT3, play an essential role in hematological disorders onset and progress upon mutations, dysfunction, or hyperactivity. Besides, microRNAs, as biological molecules, has been shown to play a dual role in either tumorigenesis and tumor suppression in various cancers. Besides, a strong association between STAT3 and miRNA has been reported. For example, miRNAs can regulate STAT3 via targeting its upstream mediators such as IL6, IL9, and JAKs or directly binding to the STAT3 gene. On the other hand, STAT3 can regulate miRNAs. In this review study, we aimed to determine the role of either microRNAs and STAT3 along with their effect on one another's activity and function in hematological malignancies.

The snapshot of metabolic health in evaluating micronutrient status, the risk of infection and clinical outcome of COVID-19

COVID-19 has re-established the significance of analyzing the organism through a metabolic perspective to uncover the dynamic interconnections within the biological systems. The role of micronutrient status and metabolic health emerge as pivotal in COVID-19 pathogenesis and the immune system's response. Metabolic disruption, proceeding from modifiable factors, has been proposed as a significant risk factor accounting for infection susceptibility, disease severity and risk for post-COVID complications. Metabolomics, the comprehensive study and quantification of intermediates and products of metabolism, is a rapidly evolving field and a novel tool in biomarker discovery. In this article, we propose that leveraging insulin resistance biomarkers along with biomarkers of micronutrient deficiencies, will allow for a diagnostic window and provide functional therapeutic targets. Specifically, metabolomics can be applied as: a. At-home test to assess the risk of infection and propose nutritional support, b. A screening tool for high-risk COVID-19 patients to develop serious illness during hospital admission and prioritize medical support, c(i). A tool to match nutritional support with specific nutrient requirements for mildly ill patients to reduce the risk for hospitalization, and c(ii). for critically ill patients to reduce recovery time and risk of post-COVID complications, d. At-home test to monitor metabolic health and reduce post-COVID symptomatology. Metabolic rewiring offers potential virtues towards disease prevention, dissection of high-risk patients, taking actionable therapeutic measures, as well as shielding against post-COVID syndrome.

Clinical Significance of Micronutrient Supplementation in Critically Ill COVID-19 Patients with Severe ARDS

The interplay between inflammation and oxidative stress is a vicious circle, potentially resulting in organ damage. Essential micronutrients such as selenium (Se) and zinc (Zn) support anti-oxidative defense systems and are commonly depleted in severe disease. This single-center retrospective study investigated micronutrient levels under Se and Zn supplementation in critically ill patients with COVID-19 induced acute respiratory distress syndrome (ARDS) and explored potential relationships with immunological and clinical parameters. According to intensive care unit (ICU) standard operating procedures, patients received 1.0 mg of intravenous Se daily on top of artificial nutrition, which contained various amounts of Se and Zn. Micronutrients, inflammatory cytokines, lymphocyte subsets and clinical data were extracted from the patient data management system on admission and after 10 to 14 days of treatment. Forty-six patients were screened for eligibility and 22 patients were included in the study. Twenty-one patients (95%) suffered from severe ARDS and 14 patients (64%) survived to ICU discharge. On admission, the majority of patients had low Se status biomarkers and Zn levels, along with elevated inflammatory parameters. Se supplementation significantly elevated Se (p = 0.027) and selenoprotein P levels (SELENOP; p = 0.016) to normal range. Accordingly, glutathione peroxidase 3 (GPx3) activity increased over time (p = 0.021). Se biomarkers, most notably SELENOP, were inversely correlated with CRP (r_s = −0.495), PCT (r_s = −0.413), IL-6 (r_s = −0.429), IL-1β (r_s = −0.440) and IL-10 (r_s = −0.461). Positive associations were found for CD8⁺ T cells (r_s = 0.636), NK cells (r_s = 0.772), total IgG (r_s = 0.493) and PaO₂/FiO₂ ratios (r_s = 0.504). In addition, survivors tended to have higher Se levels after 10 to 14 days compared to non-survivors (p = 0.075). Sufficient Se and Zn levels may potentially be of clinical significance for an adequate immune response in critically ill patients with severe COVID-19 ARDS.

Attenuating the Effects of Novel COVID-19 (SARS-CoV-2) Infection-Induced Cytokine Storm and the Implications

The COVID-19 pandemic constitutes an arduous global health challenge, and the increasing number of fatalities calls for the speedy pursuit of a remedy. This review emphasizes the changing aspects of the COVID-19 disease, featuring the cytokine storm's pathological processes. Furthermore, we briefly reviewed potential therapeutic agents that may modulate and alleviate cytokine storms. The literature exploration was made using PubMed, Embase, MEDLINE, Google scholar, and China National Knowledge Infrastructure databases to retrieve the most recent literature on the etiology, diagnostic markers, and the possible prophylactic and therapeutic options for the management of cytokine storm in patients hospitalized with COVID-19 disease. The causative agent, severe acute respiratory coronavirus-2 (SARS-CoV-2), continually threatens the efficiency of the immune system of the infected individuals. As the first responder, the innate immune system provides primary protection against COVID-19, affecting the disease's progression, clinical outcome, and prognosis. Evidence suggests that the fatalities associated with COVID-19 are primarily due to hyper-inflammation and an aberrant immune function. Accordingly, the magnitude of the release of pro-inflammatory cytokines such as interleukin (IL)-1, (IL-6), and tumor necrosis alpha (TNF-α) significantly differentiate between mild and severe cases of COVID-19. The early prediction of a cytokine storm is made possible by several serum chemistry and hematological markers. The prompt use of these markers for diagnosis and the aggressive prevention and management of a cytokine release syndrome is critical in determining the level of morbidity and fatality associated with COVID-19. The prophylaxis and the rapid treatment of cytokine storm by clinicians will significantly enhance the fight against the dreaded COVID-19 disease.

Contribution of STAT3 to the pathogenesis of COVID-19

Hyper-inflammatory responses, lymphopenia, unbalanced immune responses, cytokine storm, large viral replication and massive cell death play fundamental roles in the pathogenesis of COVID-19. Extreme production of many kinds of pro-inflammatory cytokines and chemokines occur in severe COVID-19 that called cytokine storm. Signal transducer and activator of transcription-3 (STAT-3) present in the cytoplasm in an inactive form and can be stimulated by a vast range of cytokines, chemokines and growth factors. Thus, STAT-3 can participate in the induction of inflammatory responses during coronavirus infections. STAT-3 can also suppress anti-virus interferon response and induce unbalanced anti-virus adaptive immune response, through influencing Th17-, Th1-, Treg-, and B cell-mediated functions. Furthermore, STAT-3 can contribute to the M2 macrophage polarization, lung fibrosis and thrombosis. Moreover, STAT-3 may be directly targeted by some virus-derived protein and operate as a pro-viral or anti-viral element in a virus-specific process. Here, the possible contribution of STAT-3 to the pathogenesis of COVID-19 was explained, while providing potential approaches to target this transcription factor in an attempt for COVID-19 treatment.

Severe Acute Respiratory Syndrome-Associated Coronavirus 2 Infection and Organ Dysfunction in the ICU: Opportunities for Translational Research

OBJECTIVES

Since the beginning of the coronavirus disease 2019 pandemic, hundreds of thousands of patients have been treated in ICUs across the globe. The severe acute respiratory syndrome-associated coronavirus 2 virus enters cells via the angiotensin-converting enzyme 2 receptor and activates several distinct inflammatory pathways, resulting in hematologic abnormalities and dysfunction in respiratory, cardiac, gastrointestinal renal, endocrine, dermatologic, and neurologic systems. This review summarizes the current state of research in coronavirus disease 2019 pathophysiology within the context of potential organ-based disease mechanisms and opportunities for translational research.

DATA SOURCES

Investigators from the Research Section of the Society of Critical Care Medicine were selected based on expertise in specific organ systems and research focus. Data were obtained from searches conducted in Medline via the PubMed portal, Directory of Open Access Journals, Excerpta Medica database, Latin American and Caribbean Health Sciences Literature, and Web of Science from an initial search from December 2019 to October 15, 2020, with a revised search to February 3, 2021. The medRxiv, Research Square, and clinical trial registries preprint servers also were searched to limit publication bias.

STUDY SELECTION

Content experts selected studies that included mechanism-based relevance to the severe acute respiratory syndrome-associated coronavirus 2 virus or coronavirus disease 2019 disease.

DATA EXTRACTION

Not applicable.

DATA SYNTHESIS

Not applicable.

CONCLUSIONS

Efforts to improve the care of critically ill coronavirus disease 2019 patients should be centered on understanding how severe acute respiratory syndrome-associated coronavirus 2 infection affects organ function. This review articulates specific targets for further research.

Circulating mitochondrial DNA is an early indicator of severe illness and mortality from COVID-19

BackgroundMitochondrial DNA (MT-DNA) are intrinsically inflammatory nucleic acids released by damaged solid organs. Whether circulating cell-free MT-DNA quantitation could be used to predict the risk of poor COVID-19 outcomes remains undetermined.MethodsWe measured circulating MT-DNA levels in prospectively collected, cell-free plasma samples from 97 subjects with COVID-19 at hospital presentation. Our primary outcome was mortality. Intensive care unit (ICU) admission, intubation, vasopressor, and renal replacement therapy requirements were secondary outcomes. Multivariate regression analysis determined whether MT-DNA levels were independent of other reported COVID-19 risk factors. Receiver operating characteristic and area under the curve assessments were used to compare MT-DNA levels with established and emerging inflammatory markers of COVID-19.ResultsCirculating MT-DNA levels were highly elevated in patients who eventually died or required ICU admission, intubation, vasopressor use, or renal replacement therapy. Multivariate regression revealed that high circulating MT-DNA was an independent risk factor for these outcomes after adjusting for age, sex, and comorbidities. We also found that circulating MT-DNA levels had a similar or superior area under the curve when compared against clinically established measures of inflammation and emerging markers currently of interest as investigational targets for COVID-19 therapy.ConclusionThese results show that high circulating MT-DNA levels are a potential early indicator for poor COVID-19 outcomes.FundingWashington University Institute of Clinical Translational Sciences COVID-19 Research Program and Washington University Institute of Clinical Translational Sciences (ICTS) NIH grant UL1TR002345.

Obesity-induced inflammation: The impact of the hematopoietic stem cell niche

Obesity and obesity-related diseases like type 2 diabetes (T2D) are prominent global health issues; therefore, there is a need to better understand the mechanisms underlying these conditions. The onset of obesity is characterized by accumulation of proinflammatory cells, including Ly6c^hi monocytes (which differentiate into proinflammatory macrophages) and neutrophils, in metabolic tissues. This shift toward chronic, low-grade inflammation is an obese-state hallmark and highly linked to metabolic disorders and other obesity comorbidities. The mechanisms that induce and maintain increased inflammatory myelopoiesis are of great interest, with a recent focus on how obesity affects more primitive hematopoietic cells. The hematopoietic system is constantly replenished by proper regulation of hematopoietic stem and progenitor (HSPC) pools in the BM. While early research suggests that chronic obesity promotes expansion of myeloid-skewed HSPCs, the involvement of the hematopoietic stem cell (HSC) niche in regulating obesity-induced myelopoiesis remains undefined. In this review, we explore the role of the multicellular HSC niche in hematopoiesis and inflammation, and the potential contribution of this niche to the hematopoietic response to obesity. This review further aims to summarize the potential HSC niche involvement as a target of obesity-induced inflammation and a driver of obesity-induced myelopoiesis.

T cell response to SARS-CoV-2 infection in humans: A systematic review

BACKGROUND

Understanding the T cell response to SARS-CoV-2 is critical to vaccine development, epidemiological surveillance and disease control strategies. This systematic review critically evaluates and synthesises the relevant peer-reviewed and pre-print literature published from 01/01/2020-26/06/2020.

METHODS

For this systematic review, keyword-structured literature searches were carried out in MEDLINE, Embase and COVID-19 Primer. Papers were independently screened by two researchers, with arbitration of disagreements by a third researcher. Data were independently extracted into a pre-designed Excel template and studies critically appraised using a modified version of the MetaQAT tool, with resolution of disagreements by consensus. Findings were narratively synthesised.

RESULTS

61 articles were included. 55 (90%) studies used observational designs, 50 (82%) involved hospitalised patients with higher acuity illness, and the majority had important limitations. Symptomatic adult COVID-19 cases consistently show peripheral T cell lymphopenia, which positively correlates with increased disease severity, duration of RNA positivity, and non-survival; while asymptomatic and paediatric cases display preserved counts. People with severe or critical disease generally develop more robust, virus-specific T cell responses. T cell memory and effector function has been demonstrated against multiple viral epitopes, and, cross-reactive T cell responses have been demonstrated in unexposed and uninfected adults, but the significance for protection and susceptibility, respectively, remains unclear.

CONCLUSION

A complex pattern of T cell response to SARS-CoV-2 infection has been demonstrated, but inferences regarding population level immunity are hampered by significant methodological limitations and heterogeneity between studies, as well as a striking lack of research in asymptomatic or pauci-symptomatic individuals. In contrast to antibody responses, population-level surveillance of the T cell response is unlikely to be feasible in the near term. Focused evaluation in specific sub-groups, including vaccine recipients, should be prioritised.

Dynamic changes in lymphocyte subsets and parallel cytokine levels in patients with severe and critical COVID-19

Background

The lack of knowledge regarding the pathogenesis and host immune response during SARS-CoV-2 infection has limited the development of effective treatments. Thus, we longitudinally investigated the dynamic changes in peripheral blood lymphocyte subsets and parallel changes in cytokine levels in COVID-19 patients with different disease severities to further address disease pathogenesis.

Methods

A total of 67 patients (10 moderate, 38 severe and 19 critical cases) with COVID-19 admitted to a tertiary care hospital in Wuhan from February 8th to April 6th, 2020 were retrospectively studied. Dynamic data of lymphocyte subsets and inflammatory cytokines were collected.

Results

On admission, compared with moderate cases, severe and critical cases showed significantly decreased levels of total lymphocytes, T lymphocytes, CD4⁺ T cells, CD8⁺ T cells, B cells and NK cells. IL-6 and IL-10 were significantly higher in the critical group. During the following hospitalization period, most of the lymphocyte subsets in the critical group began to recover to levels comparable to those in the severe group from the fourth week after illness onset, except for NK cells, which recovered after the sixth week. A sustained decrease in the lymphocyte subsets and an increase in IL-6 and IL-10 were observed in the nonsurvivors until death. There was a strong negative correlation between IL-6 and IL-10 and total lymphocytes, T lymphocytes, CD4⁺ T cells, CD8⁺ T cells and NK cells.

Conclusions

A sustained decrease in lymphocyte subsets, especially CD4⁺ T cells and NK cells, interacting with proinflammatory cytokine storms was associated with severe disease and poor prognosis in COVID-19.

Multisystem Inflammatory Syndrome in Children (MIS-C), a Post-viral Myocarditis and Systemic Vasculitis-A Critical Review of Its Pathogenesis and Treatment

MIS-C is a newly defined post-viral myocarditis and inflammatory vasculopathy of children following COVID-19 infection. This review summarizes the literature on diagnosis, parameters of disease severity, and current treatment regimens. The clinical perspective was analyzed in light of potential immunopathogenesis and compared to other post-infectious and inflammatory illnesses of children affecting the heart. In this paradigm, the evidence supports the importance of endothelial injury and activation of the IL-1 pathway as a common determinant among MIS-C, Kawasaki disease, and Acute Rheumatic fever.

Protective Potentials of Type III Interferons in COVID-19 Patients: Lessons from Differential Properties of Type I- and III Interferons

While an appropriately regulated production of interferons (IFNs) performs a fundamental role in the defense against coronaviruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), dysregulated overproduction of inflammatory mediators can play an important role in the development of SARS-CoV-2 infection-related complications, such as acute respiratory distress syndrome. As the principal constituents of innate immunity, both type I and III IFNs share antiviral features. However, important properties, including preferential expression at mucosal barriers (such as respiratory tract), local influences, lower receptor distribution, smaller target cell types, noninflammatory effects, and immunomodulatory impacts, were attributed only to type III IFNs. Accordingly, type III IFNs can establish an optimal effective antiviral response, without triggering exaggerated systemic inflammation that is generally attributed to the type I IFNs. However, some harmful effects were attributed to the III IFNs and there are also major differences between human and mouse concerning the immunomodulatory effects of III IFNs. Here, we describe the differential properties of type I and type III IFNs and present a model of IFN response during SARS-COV-2 infection, while highlighting the superior potential of type III IFNs in COVID-19.

Autoinflammatory and autoimmune conditions at the crossroad of COVID-19

Coronavirus disease 2019 (COVID-19) has been categorized as evolving in overlapping phases. First, there is a viral phase that may well be asymptomatic or mild in the majority, perhaps 80% of patients. The pathophysiological mechanisms resulting in minimal disease in this initial phase are not well known. In the remaining 20% of cases, the disease may become severe and/or critical. In most patients of this latter group, there is a phase characterized by the hyperresponsiveness of the immune system. A third phase corresponds to a state of hypercoagulability. Finally, in the fourth stage organ injury and failure occur. Appearance of autoinflammatory/autoimmune phenomena in patients with COVID-19 calls attention for the development of new strategies for the management of life-threatening conditions in critically ill patients. Antiphospholipid syndrome, autoimmune cytopenia, Guillain-Barré syndrome and Kawasaki disease have each been reported in patients with COVID-19. Here we present a scoping review of the relevant immunological findings in COVID-19 as well as the current reports about autoinflammatory/autoimmune conditions associated with the disease. These observations have crucial therapeutic implications since immunomodulatory drugs are at present the most likely best candidates for COVID-19 therapy. Clinicians should be aware of these conditions in patients with COVID-19, and these observations should be considered in the current development of vaccines.

Microbial sensing by haematopoietic stem and progenitor cells: Vigilance against infections and immune education of myeloid cells

Bone marrow haematopoietic stem and progenitor cells (HSPCs) express pattern recognition receptors such as Toll-like receptors (TLRs) to sense microbial products and activation of these innate immune receptors induces cytokine expression and redirects bone marrow haematopoiesis towards the increased production of myeloid cells. Secreted cytokines by HSPCs in response to TLR ligands can act in an autocrine or paracrine manner to regulate haematopoiesis. Moreover, tonic activation of HSPCs by microbiota-derived compounds might educate HSPCs to produce superior myeloid cells equipped with innate memory responses to combat pathogens. While haematopoietic stem cell activation through TLRs meets the increased demand for blood leucocytes to protect the host against infection, persistent exposure to inflammatory cytokines or microbial products might impair their function and even induce malignant transformation. This review highlights the potential outcomes of HSPCs in response to TLR ligands.

Pro- and Anti-Inflammatory Responses in Severe COVID-19-Induced Acute Respiratory Distress Syndrome-An Observational Pilot Study

Objectives

The severity of Coronavirus Disease 2019 (COVID-19) is largely determined by the immune response. First studies indicate altered lymphocyte counts and function. However, interactions of pro- and anti-inflammatory mechanisms remain elusive. In the current study we characterized the immune responses in patients suffering from severe COVID-19-induced acute respiratory distress syndrome (ARDS).

Methods

This was a single-center retrospective study in patients admitted to the intensive care unit (ICU) with confirmed COVID-19 between March 14th and May 28th 2020 (n = 39). Longitudinal data were collected within routine clinical care, including flow-cytometry of lymphocyte subsets, cytokine analysis and growth differentiation factor 15 (GDF-15). Antibody responses against the receptor binding domain (RBD) of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Spike protein were analyzed.

Results

All patients suffered from severe ARDS, 30.8% died. Interleukin (IL)-6 was massively elevated at every time-point. The anti-inflammatory cytokine IL-10 was concomitantly upregulated with IL-6. The cellular response was characterized by lymphocytopenia with low counts of CD8+ T cells, natural killer (NK) and naïve T helper cells. CD8+ T and NK cells recovered after 8 to 14 days. The B cell system was largely unimpeded. This coincided with a slight increase in anti-SARS-CoV-2-Spike-RBD immunoglobulin (Ig) G and a decrease in anti-SARS-CoV-2-Spike-RBD IgM. GDF-15 levels were elevated throughout ICU treatment.

Conclusions

Massively elevated levels of IL-6 and a delayed cytotoxic immune defense characterized severe COVID-19-induced ARDS. The B cell response and antibody production were largely unimpeded. No obvious imbalance of pro- and anti-inflammatory mechanisms was observed, with elevated GDF-15 levels suggesting increased tissue resilience.

Lymphopenia an important immunological abnormality in patients with COVID-19: Possible mechanisms

The lymphopenia as a major immunological abnormality occurs in the majority of severe COVID-19 patients, which is strongly associated with mortality rate. A low proportion of lymphocytes may express the main receptor for SARS-CoV-2, called angiotensin-converting enzyme 2 (ACE2). Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can also use ACE2-independent pathways to enter lymphocytes. Both SARS-CoV-2- and immune-mediated mechanisms may contribute to the occurrence of lymphopenia through influencing the lymphocyte production, survival or tissue re-distribution. The metabolic and biochemical changes can also affect the production and survival of lymphocytes in COVID-19 patients. Lymphopenia can cause general immunosuppression and promote cytokine storm, both of them play an important role in the viral persistence, viral replication, multi-organ failure and eventually death. Here, a comprehensive view concerning the possible mechanisms that may lead to the lymphocyte reduction in COVID-19 patients is provided, while highlighting the potential intervention approaches to prevent lymphopenia.

Circulating Mitochondrial DNA is an Early Indicator of Severe Illness and Mortality from COVID-19

Mitochondrial DNA (MT-DNA) are intrinsically inflammatory nucleic acids released by damaged solid organs. Whether the appearance of cell-free MT-DNA is linked to poor COVID-19 outcomes remains undetermined. Here, we quantified circulating MT-DNA in prospectively collected, cell-free plasma samples from 97 subjects with COVID-19 at the time of hospital presentation. Circulating MT-DNA were sharply elevated in patients who eventually died, required ICU admission or intubation. Multivariate regression analysis revealed that high circulating MT-DNA levels is an independent risk factor for all of these outcomes after adjusting for age, sex and comorbidities. Additionally, we found that circulating MT-DNA has a similar or superior area-under-the curve when compared to clinically established measures of systemic inflammation, as well as emerging markers currently of interest as investigational targets for COVID-19 therapy. These results show that high circulating MT-DNA levels is a potential indicator for poor COVID-19 outcomes.

Reactive Myelopoiesis Triggered by Lymphodepleting Chemotherapy Limits the Efficacy of Adoptive T Cell Therapy

Adoptive T cell therapy (ACT) in combination with lymphodepleting chemotherapy is an effective strategy to induce the eradication of tumors, providing long-term regression in cancer patients. Despite that lymphodepleting regimens condition the host for optimal engraftment and expansion of adoptively transferred T cells, lymphodepletion concomitantly promotes immunosuppression during the course of endogenous immune recovery. In this study, we have identified that lymphodepleting chemotherapy initiates the mobilization of hematopoietic progenitor cells that differentiate to immunosuppressive myeloid cells, leading to a dramatic increase of peripheral myeloid-derived suppressor cells (MDSCs). In melanoma and lung cancer patients, MDSCs rapidly expanded in the periphery within 1 week after completion of a lymphodepleting regimen and infusion of autologous tumor-infiltrating lymphocytes (TILs). This expansion was associated with disease progression, poor survival, and reduced TIL persistence in melanoma patients. We demonstrated that the interleukin 6 (IL-6)-driven differentiation of mobilized hematopoietic progenitor cells promoted the survival and immunosuppressive capacity of post-lymphodepletion MDSCs. Furthermore, the genetic abrogation or therapeutic inhibition of IL-6 in mouse models enhanced host survival and reduced tumor growth in mice that received ACT. Thus, the expansion of MDSCs in response to lymphodepleting chemotherapy may contribute to ACT failure, and targeting myeloid-mediated immunosuppression may support anti-tumor immune responses.

Do haematopoietic stem cells age?

Genetic defects that accumulate in haematopoietic stem cells (HSCs) are thought to be responsible for age-related changes in haematopoiesis that include a decline in lymphopoiesis and skewing towards the myeloid lineage. This HSC-centric view is based largely on studies showing that HSCs from aged mice exhibit these lineage biases following transplantation into irradiated young recipient mice. In this Opinion article, we make the case that the reliance on this approach has led to inaccurate conclusions regarding the effects of ageing on blood-forming stem cells; we suggest instead that changes in the environment contribute to haematopoietic system ageing. We propose that a complete understanding of how ageing affects haematopoiesis depends on the analysis of blood cell production in unperturbed mice. We describe how this can be achieved using in situ fate mapping. This approach indicates that changes in downstream progenitors, in addition to any HSC defects, may explain the reduced lymphopoiesis and sustained myelopoiesis that occur during ageing.

mTORC1 activity is essential for erythropoiesis and B cell lineage commitment

Mechanistic target of rapamycin (mTOR) is a serine/threonine protein kinase that mediates phosphoinositide-3-kinase (PI3K)/AKT signalling. This pathway is involved in a plethora of cellular functions including protein and lipid synthesis, cell migration, cell proliferation and apoptosis. In this study, we proposed to delineate the role of mTORC1 in haemopoietic lineage commitment using knock out (KO) mouse and cell line models. Mx1-cre and Vav-cre expression systems were used to specifically target Raptorfl/fl (mTORC1), either in all tissues upon poly(I:C) inoculation, or specifically in haemopoietic stem cells, respectively. Assessment of the role of mTORC1 during the early stages of development in Vav-cre+Raptorfl/fl mice, revealed that these mice do not survive post birth due to aberrations in erythropoiesis resulting from an arrest in development at the megakaryocyte-erythrocyte progenitor stage. Furthermore, Raptor-deficient mice exhibited a block in B cell lineage commitment. The essential role of Raptor (mTORC1) in erythrocyte and B lineage commitment was confirmed in adult Mx1-cre+Raptorfl/fl mice upon cre-recombinase induction. These studies were supported by results showing that the expression of key lineage commitment regulators, GATA1, GATA2 and PAX5 were dysregulated in the absence of mTORC1-mediated signals. The regulatory role of mTOR during erythropoiesis was confirmed in vitro by demonstrating a reduction of K562 cell differentiation towards RBCs in the presence of established mTOR inhibitors. While mTORC1 plays a fundamental role in promoting RBC development, we showed that mTORC2 has an opposing role, as Rictor-deficient progenitor cells exhibited an elevation in RBC colony formation ex vivo. Collectively, our data demonstrate a critical role played by mTORC1 in regulating the haemopoietic cell lineage commitment.

Plasma Cells Are Obligate Effectors of Enhanced Myelopoiesis in Aging Bone Marrow

Aging results in increased myelopoiesis, which is linked to the increased incidence of myeloid leukemias and production of myeloid-derived suppressor cells. Here, we examined the contribution of plasma cells (PCs) to age-related increases in myelopoiesis, as PCs exhibit immune regulatory function and sequester in bone marrow (BM). PC number was increased in old BM, and they exhibited high expression of genes encoding inflammatory cytokines and pathogen sensors. Antibody-mediated depletion of PCs from old mice reduced the number of myeloid-biased hematopoietic stem cells and mature myeloid cells to levels in young animals, but lymphopoiesis was not rejuvenated, indicating that redundant mechanisms inhibit that process. PCs also regulated the production of inflammatory factors from BM stromal cells, and disruption of the PC-stromal cell circuitry with inhibitors of the cytokines IL-1 and TNF-α attenuated myelopoiesis in old mice. Thus, the age-related increase in myelopoiesis is driven by an inflammatory network orchestrated by PCs.

Systemic immune-inflammation index could estimate the cross-sectional high activity and the poor outcomes in immunosuppressive drug-naïve patients with antineutrophil cytoplasmic antibody-associated vasculitis

OBJECTIVES

We investigated whether systemic immune-inflammation index (SII) at diagnosis can estimate the cross-sectional high activity and predict the poor outcomes in immunosuppressive drug-naïve patients with antineutrophil cytoplasmic antibody-associated vasculitis (AAV).

METHODS

We retrospectively reviewed the medical records of 163 patients with AAV and obtained clinical and laboratory data. We calculated Birmingham vasculitis activity score (BVAS) as well as five-factor score (FFS) (2009) at diagnosis. SII at diagnosis was calculated by the equation of (SII at diagnosis = platelet count × neutrophil count/lymphocyte count at diagnosis). Severe AAV was defined as BVAS at diagnosis ≥16. The odds ratio was assessed using the multivariable logistic regression analysis and cumulative survival rates were compared by the Kaplan-Meier survival analysis.

RESULTS

The median age at diagnosis was 58.0 years old and 51 patients were men. The median BVAS was 12.0. Fifty-seven patients had severe AAV. The median SII at diagnosis was 1349.6. In the multivariable analysis, only SII exhibited a significant odds ratio for the cross-sectional severe AAV (P = 0.043). We obtained the cut-off of SII at diagnosis for severe AAV as 1573.56. Patients with SII at diagnosis ≥1573.56 exhibited a significantly high relative risk of the cross-sectional severe AAV compared to those without (relative risk 4.625). Furthermore, patients with SII at diagnosis ≥1573.56 exhibited significantly the lower cumulative relapse free and renal survivals than those without.

CONCLUSION

Systemic immune-inflammation index at diagnosis could estimate the cross-section severe AAV and predict the poor outcomes in AAV patients.

Lymphoid-Biased Hematopoietic Stem Cells Are Maintained with Age and Efficiently Generate Lymphoid Progeny

Current models propose that reductions in the number of lymphoid-biased hematopoietic stem cells (Ly-HSCs) underlie age-related declines in lymphopoiesis. We show that Ly-HSCs do not decline in number with age. Old Ly-HSCs exhibit changes in gene expression and a myeloid-biased genetic profile, but we demonstrate that they retain normal lymphoid potential when removed from the old in vivo environment. Additional studies showing that interleukin-1 inhibits Ly-HSC lymphoid potential provide support for the hypothesis that increased production of inflammatory cytokines during aging underlies declines in lymphocyte production. These results indicate that current models proposing that lymphopoiesis declines with age due to loss of Ly-HSCs require revision and provide an additional perspective on why lymphocyte development in the elderly is attenuated.

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Ly-HSCs do not decline in number with age

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Transcriptome changes in old Ly-HSCs result in the acquisition of a myeloid signature

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Ly-HSCs efficiently generate lymphocytes when removed from the old environment

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IL-1 blocks lymphoid potential from Ly-HSCs and My-HSCs

Regulation of hematopoietic cell signaling by SHIP-1 inositol phosphatase: growth factors and beyond

SHIP-1 is a hematopoietic-specific inositol phosphatase activated downstream of a multitude of receptors including those for growth factors, cytokines, antigen, immunoglobulin and toll-like receptor agonists where it exerts inhibitory control. While it is constitutively expressed in all immune cells, SHIP-1 expression is negatively regulated by the inflammatory and oncogenic micro-RNA miR-155. Knockout mouse studies have shown the importance of SHIP-1 in various immune cell subsets and have revealed a range of immune-mediated pathologies that are engendered due to loss of SHIP-1's regulatory activity, impelling investigations into the role of SHIP-1 in human disease. In this review, we provide an overview of the literature relating to the role of SHIP-1 in hematopoietic cell signaling and function, we summarize recent reports that highlight the dysregulation of the SHIP-1 pathway in cancers, autoimmune disorders and inflammatory diseases, and lastly we discuss the importance of SHIP-1 in restraining myeloid growth factor signaling.

Overexpression of miR-574-3p suppresses proliferation and induces apoptosis of chronic myeloid leukemia cells via targeting IL6/JAK/STAT3 pathway

The present study aimed to elucidate the potential roles and regulatory mechanism of microRNA (miR)-574-3p in the development of chronic myeloid leukemia (CML). The expression of miR-574-3p in peripheral blood obtained from patients with CML was examined. Subsequently, miR-574-3p was overexpressed and suppressed in CML K562 cells to further investigate the effects of miR-574-3p on cell proliferation, and apoptosis. Furthermore, a luciferase reporter assay was performed to investigate whether interleukin-6 (IL-6) was a target of miR-574-3p. In addition, the regulatory association between miR-574-3p and the IL-6/Janus kinase (JNK)/signal transducer and activator of transcription-3 (STAT3) signaling pathway was explored. The expression of miR-574-3p in the peripheral blood obtained from patients with CML was significantly lower compared with that in healthy controls. Overexpression of miR-574-3p significantly inhibited the proliferation and induced the apoptosis of K562 cells, whereas suppression of miR-574-3p exhibited opposite effects. In addition, IL-6 was identified to be a direct target of miR-574-3p. Overexpression of IL-6 significantly promoted the proliferation and inhibited the apoptosis of K562 cells. Furthermore, overexpression of miR-574-3p inhibited the activation of the JAK/STAT3 signaling pathway, which was rescued by overexpression of IL-6. The results of the current study indicate that miR-574-3p overexpression may serve an important role in inhibiting proliferation and inducing apoptosis of K562 cells via suppression of IL-6/JAK/STAT3 signaling pathway activation. miR-574-3p may serve as a potential therapeutic target for CML.

Regulation of myelopoiesis by proinflammatory cytokines in infectious diseases

Hematopoiesis is hierarchically orchestrated by a very small population of hematopoietic stem cells (HSCs) that reside in the bone-marrow niche and are tightly regulated to maintain homeostatic blood production. HSCs are predominantly quiescent, but they enter the cell cycle in response to inflammatory signals evoked by severe systemic infection or injury. Thus, hematopoietic stem and progenitor cells (HSPCs) can be activated by pathogen recognition receptors and proinflammatory cytokines to induce emergency myelopoiesis during infection. This emergency myelopoiesis counterbalances the loss of cells and generates lineage-restricted hematopoietic progenitors, eventually replenishing mature myeloid cells to control the infection. Controlled generation of such signals effectively augments host defense, but dysregulated stimulation by these signals is harmful to HSPCs. Such hematopoietic failure often results in blood disorders including chronic inflammatory diseases and hematological malignancies. Recently, we found that interleukin (IL)-27, one of the IL-6/IL-12 family cytokines, has a unique ability to directly act on HSCs and promote their expansion and differentiation into myeloid progenitors. This process resulted in enhanced production of neutrophils by emergency myelopoiesis during the blood-stage mouse malaria infection. In this review, we summarize recent advances in the regulation of myelopoiesis by proinflammatory cytokines including type I and II interferons, IL-6, IL-27, granulocyte colony-stimulating factor, macrophage colony-stimulating factor, and IL-1 in infectious diseases.

Transcriptional and Microenvironmental Regulation of Lineage Ambiguity in Leukemia

Leukemia is characterized by the uncontrolled production of leukemic cells and impaired normal hematopoiesis. Although the combination of chemotherapies and hematopoietic stem cell transplantation has significantly improved the outcome of leukemia patients, a proportion of patients still suffer from relapse after treatment. Upon relapse, a phenomenon termed “lineage switch” is observed in a subset of leukemia patients, in which conversion of lymphoblastic leukemia to myeloid leukemia or vice versa is observed. A rare entity of leukemia called mixed-phenotype acute leukemia exhibits co-expression of markers representing two or three lineages. These two phenotypes regarding the lineage ambiguity suggest that the fate of some leukemia retain or acquire a certain degree of plasticity. Studies using animal models provide insight into how lineage specifying transcription factors can enforce or convert a fate in hematopoietic cells. Modeling lineage conversion in normal hematopoietic progenitor cells may improve our current understanding of how lineage switch occurs in leukemia. In this review, we will summarize the role of transcription factors and microenvironmental signals that confer fate plasticity to normal hematopoietic progenitor cells, and their potential to regulate lineage switching in leukemias. Future efforts to uncover the mechanisms contributing to lineage conversion in both normal hematopoiesis and leukemia may pave the way to improve current therapeutic strategies.

The antiviral restriction factor IFN-induced transmembrane protein 3 prevents cytokine-driven CMV pathogenesis

The antiviral restriction factor IFN-induced transmembrane protein 3 (IFITM3) inhibits cell entry of a number of viruses, and genetic diversity within IFITM3 determines susceptibility to viral disease in humans. Here, we used the murine CMV (MCMV) model of infection to determine that IFITM3 limits herpesvirus-associated pathogenesis without directly preventing virus replication. Instead, IFITM3 promoted antiviral cellular immunity through the restriction of virus-induced lymphopenia, apoptosis-independent NK cell death, and loss of T cells. Viral disease in Ifitm3-/- mice was accompanied by elevated production of cytokines, most notably IL-6. IFITM3 inhibited IL-6 production by myeloid cells in response to replicating and nonreplicating virus as well as following stimulation with the TLR ligands Poly(I:C) and CpG. Although IL-6 promoted virus-specific T cell responses, uncontrolled IL-6 expression in Ifitm3-/- mice triggered the loss of NK cells and subsequently impaired control of MCMV replication. Thus, IFITM3 represents a checkpoint regulator of antiviral immunity that controls cytokine production to restrict viral pathogenesis. These data suggest the utility of cytokine-targeting strategies in the treatment of virus-infected individuals with impaired IFITM3 activity.

Inflammatory Changes in Bone Marrow Microenvironment Associated with Declining B Lymphopoiesis

B lymphopoiesis arrests precipitously in rabbits such that by 2-4 mo of age, before sexual maturity, little to no B lymphopoiesis occurs in the bone marrow (BM). Previously, we showed that in mice, adipocytes inhibit B lymphopoiesis in vitro by inducing inflammatory myeloid cells, which produce IL-1β. In this study, we characterized rabbit BM after the arrest of B lymphopoiesis and found a dramatic increase in fat, increased CD11b⁺ myeloid cells, and upregulated expression of the inflammatory molecules, IL-1β and S100A9, by the myeloid cells. We added BM fat, CD11b⁺ myeloid cells, and recombinant S100A9 to B lymphopoiesis cultures and found that they inhibited B lymphopoiesis and enhanced myelopoiesis. Unlike IL-1β, which inhibits B lymphopoiesis by acting on early lymphoid progenitors, S100A9 inhibits B lymphopoiesis by acting on myeloid cells and promoting the release of inflammatory molecules, including IL-1β. Many molecules produced by adipocytes activate the NLRP3 inflammasome, and the NLRP3 inhibitor, glibenclamide, restored B lymphopoiesis and minimized induction of myeloid cells induced by adipocyte-conditioned medium in vitro. We suggest that fat provides an inflammatory microenvironment in the BM and promotes/activates myeloid cells to produce inflammatory molecules such as IL-1β and S100A9, which negatively regulate B lymphopoiesis.

BCAP inhibits proliferation and differentiation of myeloid progenitors in the steady state and during demand situations

B-cell adaptor for phosphatidylinositol 3-kinase (BCAP) is a signaling adaptor expressed in mature hematopoietic cells, including monocytes and neutrophils. Here we investigated the role of BCAP in the homeostasis and development of these myeloid lineages. BCAP^-/- mice had more bone marrow (BM) monocytes than wild-type (WT) mice, and in mixed WT:BCAP^-/- BM chimeras, monocytes and neutrophils skewed toward BCAP^-/- origin, showing a competitive advantage for BCAP^-/- myeloid cells. BCAP was expressed in BM hematopoietic progenitors, including lineage^-Sca-1⁺c-kit⁺ (LSK), common myeloid progenitor, and granulocyte/macrophage progenitor (GMP) cells. At the steady state, BCAP^-/- GMP cells expressed more IRF8 and less C/EBPα than did WT GMP cells, which correlated with an increase in monocyte progenitors and a decrease in granulocyte progenitors among GMP cells. Strikingly, BCAP^-/- progenitors proliferated and produced more myeloid cells of both neutrophil and monocyte/macrophage lineages than did WT progenitors in myeloid colony-forming unit assays, supporting a cell-intrinsic role of BCAP in inhibiting myeloid proliferation and differentiation. Consistent with these findings, during cyclophosphamide-induced myeloablation or specific monocyte depletion, BCAP^-/- mice replenished circulating monocytes and neutrophils earlier than WT mice. During myeloid replenishment after cyclophosphamide-induced myeloablation, BCAP^-/- mice had increased LSK proliferation and increased numbers of LSK and GMP cells compared with WT mice. Furthermore, BCAP^-/- mice accumulated more monocytes and neutrophils in the spleen than did WT mice during Listeria monocytogenes infection. Together, these data identify BCAP as a novel inhibitor of myelopoiesis in the steady state and of emergency myelopoiesis during demand conditions.

Bone marrow fat and the decline of B lymphopoiesis in rabbits

B lymphopoiesis is necessary to generate a diverse pool of naïve B cells that are able to respond to a broad spectrum of antigens during immune responses to pathogens and to vaccination. Rabbits have been utilized for many years to generate high affinity monoclonal and polyclonal antibodies. Specific antibodies generated in rabbits have greatly advanced scientific discoveries, but the unique qualities of rabbit B cell development have been underappreciated. Unlike in humans and mice, where B lymphopoiesis declines in mid to late life, B lymphopoiesis in rabbits arrests early in life, between 2 and 4 months of age. This review focuses on the early loss of B cell development in rabbits and the contribution of the bone marrow microenvironment to this process. We also propose directions for future research in this area, and discuss how the rabbit can be used as a model to understand the decline of B lymphopoiesis that occurs in humans late in life. Such studies will be important for developing therapeutics targeted to prevent and/or reverse declining B lymphopoiesis in the elderly, as well as boosting immunity and antibody responses after infection or vaccination.

Inhibition of B Lymphopoiesis by Adipocytes and IL-1-Producing Myeloid-Derived Suppressor Cells

B lymphopoiesis declines with age, and this decline correlates with increased adipose tissue in the bone marrow (BM). Also, adipocyte-derived factors are known to inhibit B lymphopoiesis. Using cocultures of mouse BM cells with OP9 stromal cells, we found that adipocyte-conditioned medium induces the generation of CD11b(+)Gr1(+) myeloid cells, which inhibit B cell development in vitro. Adipocyte-conditioned medium-induced CD11b(+)Gr1(+) cells express Arg1 (arginase) and Nos2 (inducible NO synthase) and suppress CD4(+) T cell proliferation, indicating that these cells are myeloid-derived suppressor cells (MDSCs). Blocking arginase and inducible NO synthase did not restore B lymphopoiesis, indicating that inhibition is not mediated by these molecules. Transwell and conditioned-medium experiments showed that MDSCs inhibit B lymphopoiesis via soluble factors, and by cytokine array we identified IL-1 as an important factor. Addition of anti-IL-1 Abs restored B lymphopoiesis in BM cultures containing MDSCs, showing that MDSC inhibition of B lymphopoiesis is mediated by IL-1. By treating hematopoietic precursors with IL-1, we found that multipotent progenitors are targets of IL-1. This study uncovers a novel function for MDSCs to inhibit B lymphopoiesis through IL-1. We suggest that inflammaging contributes to a decline of B lymphopoiesis in aged individuals, and furthermore, that MDSCs and IL-1 provide therapeutic targets for restoration of B lymphopoiesis in aged and obese individuals.