Susceptibility of hematopoietic stem cells to pathogens: role in virus/bacteria tropism and pathogenesis

Cytokine secretion in stem cells of cattle infected with bovine leukaemia virus

Introduction

Bovine leukaemia virus (BLV) is a Deltaretrovirus responsible for enzootic bovine leukosis, the most common neoplastic disease of cattle. It deregulates the immune system, favouring secondary infections and changes in the blood and lymphatic tissues. Blood homeostasis depends on functional haematopoietic stem cells (HSCs). Bone marrow is populated by these cells, which express CD34+ and CD35+ surface antigens and produce and release cytokines involved in the maintenance of haematopoiesis. The aim of the study was determination of the profile of cytokine production by CD34+ stem cells of cattle naturally infected with BLV.

Material and Methods

The HSCs were generated from the blood and lymphoid organs of cows infected with BLV and healthy control cows with immunomagnetic separation and anti-CD34+ monoclonal antibodies. Isolated CD34+ cells were cultivated for two weeks with interleukin (IL)-4 and granulocyte-macrophage colony-stimulating factor. The levels of IL-6, IL-10, IL-12p40, IL-12p70, interferon gamma (IFN-γ) and tumour necrosis factor alpha (TNF-α) were determined in culture fluid by flow cytometry.

Results

The expression of IL-6, IL-12p70 and TNF-α in blood HSCs was higher in BLV+ cows than in the control animals. In bone marrow HSCs of infected cows, IL-12, TNF-α and IFN-γ were more concentrated, but in these cows' spleen HSCs only expression of IL-10 was elevated. In HSCs isolated from the lymph nodes of leukaemic cows, only TNF-α secretion was lower than in control cows, the other cytokines being more potently secreted.

Conclusion

Infection with BLV caused statistically significant differences in cytokine expression by HSC CD34+ cells.

The CD133 and CD34 cell types in human umbilical cord blood have the capacity to produce infectious dengue virus particles

Although dengue virus (DENV) can establish infections in hematopoietic stem progenitor cells (HSPCs), there is little information on dengue virus persistent infection in CD34+ and CD133+ cell surface glycoproteins of hematopoietic stem cells (HSCs). CD34 and CD133 also function as cell-cell adhesion factors, which are present in umbilical cord blood (UCB). In this study, we sought to establish a persistent infection model of DENV infection in UCB using a prolonged period of infection lasting 30 days. Post-infection, the results exhibited a productive and non-productive phase of DENV production. Using a plaque assay, Western blot, and confocal microscopy, we demonstrated that CD133 and CD34 cells are target cells for DENV infection. Moreover, we showed that DENV particles can be recovered from the non-productive phase of DENV-infected CD34 and CD133 cells after co-incubation with Vero cells. We concluded that CD133 and CD34 retain their capacity to produce the infectious virus due to proliferation and their ability to repopulate, as deduced from a BrdU proliferation assay and flow cytometry analysis using t-distributed stochastic neighbor embedding. In summary, the platform to co-culture infected primitive HSCs from their non-productive phase onto Vero cells will give new insights into understanding the DENV dynamics in cell-to-cell transmission and reactivation of the virus.

Hematopoietic stem cells and betaherpesvirus latency

The human betaherpesviruses including human cytomegalovirus (HCMV), human herpesvirus (HHV)-6a and HHV-6b, and HHV-7 infect and establish latency in CD34+ hematopoietic stem and progenitor cells (HPCs). The diverse repertoire of HPCs in humans and the complex interactions between these viruses and host HPCs regulate the viral lifecycle, including latency. Precise manipulation of host and viral factors contribute to preferential maintenance of the viral genome, increased host cell survival, and specific manipulation of the cellular environment including suppression of neighboring cells and immune control. The dynamic control of these processes by the virus regulate inter- and intra-host signals critical to the establishment of chronic infection. Regulation occurs through direct viral protein interactions and cellular signaling, miRNA regulation, and viral mimics of cellular receptors and ligands, all leading to control of cell proliferation, survival, and differentiation. Hematopoietic stem cells have unique biological properties and the tandem control of virus and host make this a unique environment for chronic herpesvirus infection in the bone marrow. This review highlights the elegant complexities of the betaherpesvirus latency and HPC virus-host interactions.

Spotlight on the impact of viral infections on Hematopoietic Stem Cells (HSCs) with a focus on COVID-19 effects

Hematopoietic stem cells (HSCs) are known for their significant capability to reconstitute and preserve a functional hematopoietic system in long-term periods after transplantation into conditioned hosts. HSCs are thus crucial cellular targets for the continual repair of inherited hematologic, metabolic, and immunologic disorders. In addition, HSCs can undergo various fates, such as apoptosis, quiescence, migration, differentiation, and self-renewal. Viruses continuously pose a remarkable health risk and request an appropriate, balanced reaction from our immune system, which as well as affects the bone marrow (BM). Therefore, disruption of the hematopoietic system due to viral infection is essential. In addition, patients for whom the risk-to-benefit ratio of HSC transplantation (HSCT) is acceptable have seen an increase in the use of HSCT in recent years. Hematopoietic suppression, BM failure, and HSC exhaustion are all linked to chronic viral infections. Virus infections continue to be a leading cause of morbidity and mortality in HSCT recipients, despite recent advancements in the field. Furthermore, whereas COVID-19 manifests initially as an infection of the respiratory tract, it is now understood to be a systemic illness that significantly impacts the hematological system. Patients with advanced COVID-19 often have thrombocytopenia and blood hypercoagulability. In the era of COVID-19, Hematological manifestations of COVID-19 (i.e., thrombocytopenia and lymphopenia), the immune response, and HSCT may all be affected by the SARS-CoV-2 virus in various ways. Therefore, it is important to determine whether exposure to viral infections may affect HSCs used for HSCT, as this, in turn, may affect engraftment efficiency. In this article, we reviewed the features of HSCs, and the effects of viral infections on HSCs and HSCT, such as SARS-CoV-2, HIV, cytomegalovirus, Epstein-Barr virus, HIV, etc. Video Abstract.

Coagulopathy in SARS-CoV-2 Infected Patients: Implication for the Management of COVID-19

COVID-19 disease has led to an extraordinary inclusive health crisis globally. Elevation of D-dimer is the major remarkable abnormal coagulation test in seriously ill COVID-19 patients. In nearly 50% of COVID-19 patients, the value of D-dimer was significantly enhancing. Recent literature indicated that COVID-19 patients were at higher risk of developing disseminated intravascular coagulation. Pro-inflammatory cytokines and chemokines are some of the factors leading to these conditions. The majority of COVID-19 patients showed a higher profile of pro-inflammatory cytokines and chemokines in severe clinical conditions. Tumor necrosis factor-α (TNF-α) and interleukins (ILs) elevated in COVID-19 infected patients. TNF-α, IL-6, and IL-1 are major cytokines vital for the inhibition of intrinsic anticoagulant pathways. COVID-19 becomes a higher complication with a significant effect on blood cell production and hemostasis cascades. Deep vein thrombosis and arterial thrombosis are common complications. Changes in hematological parameters are also frequently observed in COVID-19 patients. Especially, thrombocytopenia is an indicator for poor prognosis of the disease and is highly expected and aggravates the likelihood of death of SARS-CoV-2 infected individuals. Thrombopoiesis reduction in COVID-19 patients might be due to viral abuse of the bone marrow/the viral load may affect thrombopoietin production and function. In other ways, immune-inflammation-mediated destruction and increased consumption of platelets are also the possible proposed mechanisms for thrombocytopenia. Therefore, the counting of platelet cells is an easily accessible biomarker for disease monitoring. All SARS-CoV-2 infected patients should be admitted and identifying potential higher-risk patients. It is also obligatory to provide appropriate treatments with intensive care and strict follow-up. In addition, considerations of chronic diseases are essential for better prognosis and recovery. The current review discusses coagulopathy among SARS-CoV-2 infected individuals and its complication for the management of the disease.

Thrombocytopenia in Virus Infections

Thrombocytopenia, which signifies a low platelet count usually below 150 × 10⁹/L, is a common finding following or during many viral infections. In clinical medicine, mild thrombocytopenia, combined with lymphopenia in a patient with signs and symptoms of an infectious disease, raises the suspicion of a viral infection. This phenomenon is classically attributed to platelet consumption due to inflammation-induced coagulation, sequestration from the circulation by phagocytosis and hypersplenism, and impaired platelet production due to defective megakaryopoiesis or cytokine-induced myelosuppression. All these mechanisms, while plausible and supported by substantial evidence, regard platelets as passive bystanders during viral infection. However, platelets are increasingly recognized as active players in the (antiviral) immune response and have been shown to interact with cells of the innate and adaptive immune system as well as directly with viruses. These findings can be of interest both for understanding the pathogenesis of viral infectious diseases and predicting outcome. In this review, we will summarize and discuss the literature currently available on various mechanisms within the relationship between thrombocytopenia and virus infections.

Practical guidance for the management of adults with immune thrombocytopenia during the COVID-19 pandemic

This document aims to provide practical guidance for the assessment and management of patients with thrombocytopenia, with a particular focus on immune thrombocytopenia (ITP), during the COVID‐19 pandemic. The intention is to support clinicians and, although recommendations have been provided, it is not a formal guideline. Nor is there sufficient evidence base to conclude that alternative approaches to treatment are incorrect. Instead, it is a consensus written by clinicians with an interest in ITP or coagulation disorders and reviewed by members of the UK ITP forum.

Zika virus infection studies with CD34+ hematopoietic and megakaryocyte-erythroid progenitors, red blood cells and platelets

BACKGROUND

To date, several cases of transfusion-transmitted ZIKV infections have been confirmed. Multiple studies detected prolonged occurrence of ZIKV viral RNA in whole blood as compared to plasma samples indicating potential ZIKV interaction with hematopoietic cells. Also, infection of cells from the granulocyte/macrophage lineage has been demonstrated. Patients may develop severe thrombocytopenia, microcytic anemia, and a fatal course of disease occurred in a patient with sickle cell anemia suggesting additional interference of ZIKV with erythroid and megakaryocytic cells. Therefore, we analyzed whether ZIKV propagates in or compartmentalizes with hematopoietic progenitor, erythroid, and megakaryocytic cells.

METHODS

ZIKV RNA replication, protein translation and infectious particle formation in hematopoietic cell lines as well as primary CD34⁺ HSPCs and ex vivo differentiated erythroid and megakaryocytic cells was monitored using qRT-PCR, FACS, immunofluorescence analysis and infectivity assays. Distribution of ZIKV RNA and infectious particles in spiked red blood cell (RBC) units or platelet concentrates (PCs) was evaluated.

RESULTS

While subsets of K562 and KU812Ep6^EPO cells supported ZIKV propagation, primary CD34⁺ HSPCs, MEP cells, RBCs, and platelets were non-permissive for ZIKV infection. In spiking studies, ZIKV RNA was detectable for 7 days in all fractions of RBC units and PCs, however, ZIKV infectious particles were not associated with erythrocytes or platelets.

CONCLUSION

Viral particles from plasma or contaminating leukocytes, rather than purified CD34⁺ HSPCs or the cellular component of RBC units or PCs, present the greatest risk for transfusion-transmitted ZIKV infections.

IFN Signaling in Inflammation and Viral Infections: New Insights from Fish Models

The overarching structure of the type I interferon (IFN) system is conserved across vertebrates. However, the variable numbers of whole genome duplication events during fish evolution offer opportunities for the expansion, diversification, and new functionalization of the genes that are involved in antiviral immunity. In this review, we examine how fish models provide new insights about the implication of virus-driven inflammation in immunity and hematopoiesis. Mechanisms that have been discovered in fish, such as the strong adjuvant effect of type I IFN that is used with DNA vaccination, constitute good models to understand how virus-induced inflammatory mechanisms can interfere with adaptive responses. We also comment on new discoveries regarding the role of pathogen-induced inflammation in the development and guidance of hematopoietic stem cells in zebrafish. These findings raise issues about the potential interferences of viral infections with the establishment of the immune system. Finally, the recent development of genome editing provides new opportunities to dissect the roles of the key players involved in the antiviral response in fish, hence enhancing the power of comparative approaches.

Persistence of Brucella abortus in the Bone Marrow of Infected Mice

Brucellosis is a zoonotic bacterial infection that may persist for long periods causing relapses in antibiotic-treated patients. The ability of Brucella to develop chronic infections is linked to their capacity to invade and replicate within the mononuclear phagocyte system, including the bone marrow (BM). Persistence of Brucella in the BM has been associated with hematological complications such as neutropenia, thrombocytopenia, anemia, and pancytopenia in human patients. In the mouse model, we observed that the number of Brucella abortus in the BM remained constant for up to 168 days of postinfection. This persistence was associated with histopathological changes, accompanied by augmented numbers of BM myeloid GMP progenitors, PMNs, and CD4+ lymphocytes during the acute phase (eight days) of the infection in the BM. Monocytes, PMNs, and GMP cells were identified as the cells harboring Brucella in the BM. We propose that the BM is an essential niche for the bacterium to establish long-lasting infections and that infected PMNs may serve as vehicles for dispersion of Brucella organisms, following the Trojan horse hypothesis. Monocytes are solid candidates for Brucella reservoirs in the BM.

Reduction in White Blood Cell, Neutrophil, and Red Blood Cell Counts Related to Sex, HLA, and Islet Autoantibodies in Swedish TEDDY Children at Increased Risk for Type 1 Diabetes

Islet autoantibodies (IAs) precede the clinical onset of type 1 diabetes (T1D); however, the knowledge is limited about whether the prodrome affects complete blood counts (CBCs) in 4- to 12-year-old children with increased genetic risk for T1D. This study tested whether CBCs were altered in 4- to 12-year-old children without (n = 376) or with one or several IAs against insulin, GAD65, or IA-2 (n = 72). CBC was analyzed during longitudinal follow-up in 448 Swedish children enrolled in The Environmental Determinants of Diabetes in the Young (TEDDY) study. A linear mixed-effects model was used to assess potential association between IA and CBC measurements over time. The white blood cell and neutrophil counts were reduced in children with IAs, primarily in boys. In contrast, girls had lower levels of hemoglobin and hematocrit. Positivity for multiple IAs showed the lowest counts in white blood cells and neutrophils in boys and red blood cells, hemoglobin, and hematocrit in girls. These associations were primarily observed in children with the HLA-DR3-DQ2/DR4-DQ8 genotype. We conclude that the reduction in neutrophils and red blood cells in children with multiple IAs and HLA-DR3-DQ2/DR4-DQ8 genotype may signal a sex-dependent islet autoimmunity detected in longitudinal CBCs.

Porcine reproductive and respiratory syndrome type 1 viruses induce hypoplasia of erythroid cells and myeloid cell hyperplasia in the bone marrow of experimentally infected piglets independently of the viral load and virulence

Porcine reproductive and respiratory syndrome viruses (PRRSV) present a wide phenotypic and genetic diversity. Experimental infections have demonstrated viral replication, including highly pathogenic strains (HP-PRRSV), in primary lymphoid organs such as the thymus. However, studies of the bone marrow are scarce but necessary to help elucidate the immunobiology of PRRSV strains of differing virulence. In this study, whereas viral RNA was detected within the bone marrow of animals experimentally infected with both low virulent Lelystad (LV) and 215-06 PRRSV-1 strains and with the highly virulent SU1-bel strain, PRRSV positive cells were only occasionally detected in one SU1-bel infected animal. PRRSV RNA levels were associated to circulating virus with the highest levels detected in LV-infected pigs. At 3 dpi, a decrease in the proportion of haematopoietic tissue and number of erythroid cells in all infected groups was associated with an increase in TUNEL or cleaved caspase 3 labelling and higher counts of myeloid cells compared to control. The expression of IL-1α and IL-6 was elevated at the beginning of the infection in all infected animals. The expression of TNF-α was increased at the end of the study in all infected groups with respect to control. Different PRRSV-1 strains induced, presummably by indirect mechanisms and independently of viral load and strain virulence, moderate and sustained hypoplasia of erythroid cells and myeloid cell hyperplasia at early stages of infection. These changes were paralleled by a peak in the local expression of IL-1α, IL-6 and TNF-α in all infected groups.

Thrombocytopenia and infections

INTRODUCTION

Acquired thrombocytopenia recognizes a myriad of causes. Among these, infectious diseases play a relevant role since a low platelet count is commonplace along with other abnormal laboratory data. Areas covered: This narrative review, after a brief presentation of the possible pathogenic mechanisms, is focused on the most prevalent infections associated with thrombocytopenia, namely those attributable to hepatitis C virus (HCV), human immunodeficiency virus (HIV) and Helicobacter pylori. Expert commentary: An underlying HCV or HIV infection should always be suspected in patients at risk who present with isolated thrombocytopenia. The eradication of Helicobacter pylori is advisable in infected patients with secondary immune thrombocytopenia, because this will increase the platelet count in a substantial number of cases, thus avoiding more aggressive and prolonged treatments.

Do oral bacteria alter the regenerative potential of stem cells? A concise review

Mesenchymal stem cells (MSCs) are widely recognized as critical players in tissue regeneration. New insights into stem cell biology provide evidence that MSCs may also contribute to host defence and inflammation. In case of tissue injury or inflammatory diseases, e.g. periodontitis, stem cells are mobilized towards the site of damage, thus coming in close proximity to bacteria and bacterial components. Specifically, in the oral cavity, complex ecosystems of commensal bacteria live in a mutually beneficial state with the host. However, the formation of polymicrobial biofilm communities with pathogenic properties may trigger an inadequate host inflammatory-immune response, leading to the disruption of tissue homoeostasis and development of disease. Because of their unique characteristics, MSCs are suggested as crucial regulators of tissue regeneration even under such harsh environmental conditions. The heterogeneous effects of bacteria on MSCs across studies imply the complexity underlying the interactions between stem cells and bacteria. Hence, a better understanding of stem cell behaviour at sites of inflammation appears to be a key strategy in developing new approaches for in situ tissue regeneration. Here, we review the literature on the effects of oral bacteria on cell proliferation, differentiation capacity and immunomodulation of dental-derived MSCs.

Platelets and infection - an emerging role of platelets in viral infection

Platelets are anucleate blood cells that play a crucial role in the maintenance of hemostasis. While platelet activation and elevated platelet counts (thrombocytosis) are associated with increased risk of thrombotic complications, low platelet counts (thrombocytopenia) and several platelet function disorders increase the risk of bleeding. Over the last years, more and more evidence has emerged that platelets and their activation state can also modulate innate and adaptive immune responses and low platelet counts have been identified as a surrogate marker for poor prognosis in septic patients. Viral infections often coincide with platelet activation. Host inflammatory responses result in the release of platelet activating mediators and a pro-oxidative and pro-coagulant environment, which favors platelet activation. However, viruses can also directly interact with platelets and megakaryocytes and modulate their function. Furthermore, platelets can be activated by viral antigen-antibody complexes and in response to some viruses B-lymphocytes also generate anti-platelet antibodies. All these processes contributing to platelet activation result in increased platelet consumption and removal and often lead to thrombocytopenia, which is frequently observed during viral infection. However, virus-induced platelet activation does not only modulate platelet count but also shape immune responses. Platelets and their released products have been reported to directly and indirectly suppress infection and to support virus persistence in response to certain viruses, making platelets a double-edged sword during viral infections. This review aims to summarize the current knowledge on platelet interaction with different types of viruses, the viral impact on platelet activation, and platelet-mediated modulations of innate and adaptive immune responses.

Replenishing B lymphocytes in health and disease

The path from hematopoietic stem cells (HSCs) to functional B lymphocytes has long been appreciated as a basic model of differentiation, but much clinically relevant information has also been obtained. It is now possible to conduct single cell studies with increasingly high resolution, revealing that individual stem and progenitor cells differ from each other with respect to differentiation potential and fates. B lymphopoiesis is now seen as a gradual and unsynchronized process where progenitors eventually become B lineage restricted. Major milestones have been identified, but a precise sequence need not be followed and oscillation between states is possible. It is not yet clear if this versatility has survival value, but information is accumulating about infections and age-related changes.

Hematopoietic stem cells and retroviral infection

Retroviral induced malignancies serve as ideal models to help us better understand the molecular mechanisms associated with the initiation and progression of leukemogenesis. Numerous retroviruses including AEV, FLV, M-MuLV and HTLV-1 have the ability to infect hematopoietic stem and progenitor cells, resulting in the deregulation of normal hematopoiesis and the development of leukemia/lymphoma. Research over the last few decades has elucidated similarities between retroviral-induced leukemogenesis, initiated by deregulation of innate hematopoietic stem cell traits, and the cancer stem cell hypothesis. Ongoing research in some of these models may provide a better understanding of the processes of normal hematopoiesis and cancer stem cells. Research on retroviral induced leukemias and lymphomas may identify the molecular events which trigger the initial cellular transformation and subsequent maintenance of hematologic malignancies, including the generation of cancer stem cells. This review focuses on the role of retroviral infection in hematopoietic stem cells and the initiation, maintenance and progression of hematological malignancies.

Antiangiogenic arming of an oncolytic vaccinia virus enhances antitumor efficacy in renal cell cancer models

Oncolytic vaccinia viruses have shown compelling results in preclinical cancer models and promising preliminary safety and antitumor activity in early clinical trials. However, to facilitate systemic application it would be useful to improve tumor targeting and antitumor efficacy further. Here we report the generation of vvdd-VEGFR-1-Ig, a targeted and armed oncolytic vaccinia virus. Tumor targeting was achieved by deletion of genes for thymidine kinase and vaccinia virus growth factor, which are necessary for replication in normal but not in cancer cells. Given the high vascularization typical of kidney cancers, we armed the virus with the soluble vascular endothelial growth factor (VEGF) receptor 1 protein for an antiangiogenic effect. Systemic application of high doses of vvdd-VEGFR-1-Ig resulted in cytokine induction in an immunocompromised mouse model. Upon histopathological analysis, splenic extramedullary hematopoiesis was seen in all virus-injected mice and was more pronounced in the vvdd-VEGFR-1-Ig group. Analysis of the innate immune response after intravenous virus injection revealed high transient and dose-dependent cytokine elevations. When medium and low doses were used for intratumoral or intravenous injection, vvdd-VEGFR-1-Ig exhibited a stronger antitumor effect than the unarmed control. Furthermore, expression of VEGFR-1-Ig was confirmed, and a concurrent antiangiogenic effect was seen. In an immunocompetent model, systemic vvdd-VEGFR-1-Ig exhibited superior antitumor efficacy compared to the unarmed control virus. In conclusion, the targeted and armed vvdd-VEGFR-1-Ig has promising anticancer activity in renal cell cancer models. Extramedullary hematopoiesis may be a sensitive indicator of vaccinia virus effects in mice.

B cell precursors are targets for Salmonella infection

We previously reported that, in mice, B cells are a reservoir for bacteria during Salmonella infection. Here, we show that, within the bone marrow, B cells and their precursors are targeted for infection by Salmonella enterica serovar typhimurium. Our data suggest that B cells within the bone marrow may be a bacterial niche during chronic Salmonella infection.

CpG oligodeoxynucleotides induce IL-8 expression in CD34+ cells via mitogen-activated protein kinase-dependent and NF-kappaB-independent pathways

To elucidate the role of Toll-like receptor 9 (TLR9) activation along with the intracellular signaling pathways triggered by CpG DNA in CD34+ cells, we investigated whether synthetic oligodeoxynucleotides (ODNs), containing unmethylated CpG motifs, could induce IL-8 expression in CD34+ cells through mitogen-activated protein kinase (MAPK) or nuclear factor-kappaB (NF-kappaB) pathway. We demonstrated evidence for the first time that CD34+ cells constitutively expressed TLR9. Exposure of the cells to CpG ODN resulted in a time- and dose-dependent increase of IL-8 expression, and activation of phosphorylated ERK1/2 and phosphorylated p38. In addition, CpG ODN stimulated AP-1, but not NF-kappaB, signals. Moreover, inhibitors of MAPK (U0126 and SB203580) significantly reduced the IL-8 production, while the inhibition of NF-kappaB (pyrrolidinedithiocarbamate and retrovirus containing dominant-negative IkappaB alpha plasmid) did not affect the IL-8 expression increased by CpG ODN. Moreover, co-stimulation with LPS and CpG synergistically up-regulates IL-8 in CD34+ cells. These results suggest that CpG DNA, acting on TLR9, activates CD34+ cells to express IL-8 through MAPK-dependent and NF-kappaB-independent pathways.