Infection with Anaplasma phagocytophilum induces multilineage alterations in hematopoietic progenitor cells and peripheral blood cells. Infect Immun. 2009;77:4070-4080. [PMID: 19564373 DOI: 10.1128/iai.00570-09]

When inflammatory stressors dramatically change, disease phenotypes may transform between autoimmune hematopoietic failure and myeloid neoplasms

Aplastic anemia (AA) and hypoplastic myelodysplastic syndrome are paradigms of autoimmune hematopoietic failure (AHF). Myelodysplastic syndrome and acute myeloid leukemia are unequivocal myeloid neoplasms (MNs). Currently, AA is also known to be a clonal hematological disease. Genetic aberrations typically observed in MNs are detected in approximately one-third of AA patients. In AA patients harboring MN-related genetic aberrations, a poor response to immunosuppressive therapy (IST) and an increased risk of transformation to MNs occurring either naturally or after IST are predicted. Approximately 10%-15% of patients with severe AA transform the disease phenotype to MNs following IST, and in some patients, leukemic transformation emerges during or shortly after IST. Phenotypic transformations between AHF and MNs can occur reciprocally. A fraction of advanced MN patients experience an aplastic crisis during which leukemic blasts are repressed. The switch that shapes the disease phenotype is a change in the strength of extramedullary inflammation. Both AHF and MNs have an immune-active bone marrow (BM) environment (BME). In AHF patients, an inflamed BME can be evoked by infiltrated immune cells targeting neoplastic molecules, which contributes to the BM-specific autoimmune impairment. Autoimmune responses in AHF may represent an antileukemic mechanism, and inflammatory stressors strengthen antileukemic immunity, at least in a significant proportion of patients who have MN-related genetic aberrations. During active inflammatory episodes, normal and leukemic hematopoieses are suppressed, which leads to the occurrence of aplastic cytopenia and leukemic cell regression. The successful treatment of underlying infections mitigates inflammatory stress-related antileukemic activities and promotes the penetration of leukemic hematopoiesis. The effect of IST is similar to that of treating underlying infections. Investigating inflammatory stress-powered antileukemic immunity is highly important in theoretical studies and clinical practice, especially given the wide application of immune-activating agents and immune checkpoint inhibitors in the treatment of hematological neoplasms.

Anaplasmosis encephalitis and infection of non-myeloid bone marrow precursors

Due to climate change, infections from tickborne pathogens are becoming more prevalent in the Northern Hemisphere. Human granulocytic anaplasmosis, caused by the obligate intracellular gram-negative bacteria Anaplasma phagocytophilum and carried by Ixodes ticks, can lead to morbidity and mortality in select populations. Anaplasmosis is commonly accompanied by significant cytopaenia, the pathophysiology of which remains unknown. Our case report describes an uncommon meningoencephalitic presentation of anaplasmosis with substantial anaemia and thrombocytopaenia. Additionally, we propose a mechanism of bone marrow infection and suppression by A. phagocytophilum which may be responsible for the cytopaenia in anaplasmosis and provide pictographic evidence of anaplasma in peripheral blood, cerebrospinal fluid and bone marrow.

Tuberculosis-induced aplastic crisis and atypical lymphocyte expansion in advanced myelodysplastic syndrome: A case report and review of literature

BACKGROUND

Myelodysplastic syndrome (MDS) is caused by malignant proliferation and ineffective hematopoiesis. Oncogenic somatic mutations and increased apoptosis, necroptosis and pyroptosis lead to the accumulation of earlier hematopoietic progenitors and impaired productivity of mature blood cells. An increased percentage of myeloblasts and the presence of unfavorable somatic mutations are signs of leukemic hematopoiesis and indicators of entrance into an advanced stage. Bone marrow cellularity and myeloblasts usually increase with disease progression. However, aplastic crisis occasionally occurs in advanced MDS.

CASE SUMMARY

A 72-year-old male patient was definitively diagnosed with MDS with excess blasts-1 (MDS-EB-1) based on an increase in the percentages of myeloblasts and cluster of differentiation (CD)34+ hematopoietic progenitors and the identification of myeloid neoplasm-associated somatic mutations in bone marrow samples. The patient was treated with hypomethylation therapy and was able to maintain a steady disease state for 2 years. In the treatment process, the advanced MDS patient experienced an episode of progressive pancytopenia and bone marrow aplasia. During the aplastic crisis, the bone marrow was infiltrated with sparsely distributed atypical lymphocytes. Surprisingly, the leukemic cells disappeared. Immunological analysis revealed that the atypical lymphocytes expressed a high frequency of CD3, CD5, CD8, CD16, CD56 and CD57, suggesting the activation of autoimmune cytotoxic T-lymphocytes and natural killer (NK)/NKT cells that suppressed both normal and leukemic hematopoiesis. Elevated serum levels of inflammatory cytokines, including interleukin (IL)-6, interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α), confirmed the deranged type I immune responses. This morphological and immunological signature led to the diagnosis of severe aplastic anemia secondary to large granule lymphocyte leukemia. Disseminated tuberculosis was suspected upon radiological examinations in the search for an inflammatory niche. Antituberculosis treatment led to reversion of the aplastic crisis, disappearance of the atypical lymphocytes, increased marrow cellularity and 2 mo of hematological remission, providing strong evidence that disseminated tuberculosis was responsible for the development of the aplastic crisis, the regression of leukemic cells and the activation of CD56+ atypical lymphocytes. Reinstitution of hypomethylation therapy in the following 19 mo allowed the patient to maintain a steady disease state. However, the patient transformed the disease phenotype into acute myeloid leukemia and eventually died of disease progression and an overwhelming infectious episode.

CONCLUSION

Disseminated tuberculosis can induce CD56+ lymphocyte infiltration in the bone marrow and in turn suppress both normal and leukemic hematopoiesis, resulting in the development of aplastic crisis and leukemic cell regression.

Host-pathogen interaction in arthropod vectors: Lessons from viral infections

Haematophagous arthropods can harbor various pathogens including viruses, bacteria, protozoa, and nematodes. Insects possess an innate immune system comprising of both cellular and humoral components to fight against various infections. Haemocytes, the cellular components of haemolymph, are central to the insect immune system as their primary functions include phagocytosis, encapsulation, coagulation, detoxification, and storage and distribution of nutritive materials. Plasmatocytes and granulocytes are also involved in cellular defense responses. Blood-feeding arthropods, such as mosquitoes and ticks, can harbour a variety of viral pathogens that can cause infectious diseases in both human and animal hosts. Therefore, it is imperative to study the virus-vector-host relationships since arthropod vectors are important constituents of the ecosystem. Regardless of the complex immune response of these arthropod vectors, the viruses usually manage to survive and are transmitted to the eventual host. A multidisciplinary approach utilizing novel and strategic interventions is required to control ectoparasite infestations and block vector-borne transmission of viral pathogens to humans and animals. In this review, we discuss the arthropod immune response to viral infections with a primary focus on the innate immune responses of ticks and mosquitoes. We aim to summarize critically the vector immune system and their infection transmission strategies to mammalian hosts to foster debate that could help in developing new therapeutic strategies to protect human and animal hosts against arthropod-borne viral infections.

Immune evasion strategies of major tick-transmitted bacterial pathogens

Tick-transmitted bacterial pathogens thrive in enzootic infection cycles, colonizing disparate vertebrate and arthropod tissues, often establishing persistent infections. Therefore, the evolution of robust immune evasion strategies is central to their successful persistence or transmission between hosts. To survive in nature, these pathogens must counteract a broad range of microbicidal host responses that can be localized, tissue-specific, or systemic, including a mix of these responses at the host-vector interface. Herein, we review microbial immune evasion strategies focusing on Lyme disease spirochetes and rickettsial or tularemia agents as models for extracellular and intracellular tick-borne pathogens, respectively. A better understanding of these adaptive strategies could enrich our knowledge of the infection biology of relevant tick-borne diseases, contributing to the development of future preventions.

Oral Trypanosoma cruzi Acute Infection in Mice Targets Primary Lymphoid Organs and Triggers Extramedullary Hematopoiesis

During the acute phase of Chagas disease, Trypanosoma cruzi circulation through the bloodstream leads to high tissue parasitism in the host. In primary lymphoid organs, progenitor cell reduction paralleled transient immunosuppression. Herein we showed that acute oral infection in mice promotes diffuse parasitism in bone marrow cells at 14 and 21 days post-infection (dpi), with perivascular regions, intravascular regions, and regions near the bone being target sites of parasite replication. Phenotypic analysis of hematopoietic differentiation in the bone marrow of infected mice showed that the cell number in the tissue is decreased (lineage-negative and lineage-positive cells). Interestingly, analysis of hematopoietic branching points showed that hematopoietic stem and progenitor cells (HSPCs) were significantly increased at 14 dpi. In addition, the pool of progenitors with stem plasticity (HSC-MPP3), as well as multipotent progenitors (MPPs) such as MPP4, also showed this pattern of increase. In contrast, subsequent progenitors that arise from MPPs, such as common lymphoid progenitors (CLPs), lymphoid-primed MPPs (LMPPs), and myeloid progenitors, were not enhanced; conversely, all presented numeric decline. Annexin V staining revealed that cell death increase in the initial hematopoietic branching point probably is not linked to CLPs and that myeloid progenitors decreased at 14 and 21 dpi. In parallel, our investigation provided clues that myeloid progenitor decrease could be associated with an atypical expression of Sca-1 in this population leading to a remarkable increase on LSK-like cells at 14 dpi within the HSPC compartment. Finally, these results led us to investigate HSPC presence in the spleen as a phenomenon triggered during emergency hematopoiesis due to mobilization or expansion of these cells in extramedullary sites. Splenocyte analysis showed a progressive increase in HSPCs between 14 and 21 dpi. Altogether, our study shows that the bone marrow is a target tissue in T. cruzi orally infected mice, leading to a hematopoietic disturbance with LSK-like cell bias accounting on HSPCs possibly affecting myeloid progenitor numbers. The LMPP and CLP reduction converges with defective thymocyte development. Lastly, it is tempting to speculate that the extramedullary hematopoiesis seen in the spleen is a mechanism involved in the hematological maintenance reported during the acute phase of oral T. cruzi infection.

A rare case of delayed anaplasma phagocytophilum-induced pancytopenia: A diagnostic conundrum

Introduction

Human granulocytic anaplasmosis (HGA) is a potentially fatal tick-borne disease caused by the obligate intracellular bacterium Anaplasma phagocytophilum. It is most commonly found in the Northeastern and Midwestern parts of the United States especially during spring and summer months. The clinical picture of anaplasmosis is varied ranging from common symptoms such as fever, headache and myalgia to rarer presentations such as pancytopenia.

Case presentation

We present a case of a 62 year old male who presented with watery diarrhea, fever, and pancytopenia. Although there is a broad differential for pancytopenia, a thorough history provides clues regarding the diagnosis. In our patient, a recent history of camping in Upstate New York was suggestive of an infectious etiology from a tick borne illness.

Clinical discussion

A tick-borne panel guided us to identify the diagnosis of HGA. Although the exact underlying pathogenesis of tick-borne illnesses leading to pancytopenia is still unknown, the pancytopenia is postulated to be due to a multi-nodal mechanism involving immune and non immune platelet destruction, global bone marrow suppression, hemophagocytic lymphohistiocytosis and myelosuppressive chemokines release.

Conclusion

We hope that this case report elucidates the importance of obtaining a meticulous history in guiding clinicians towards prompt diagnosis, even in instances where there may be an evolving clinical picture.

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Human granulocytic anaplasmosis (HGA) is a potentially fatal tick-borne disease caused by the obligate intracellular bacterium Anaplasma phagocytophilum.

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A prompt diagnosis and management will facilitate an early recovery and prevent any fatal complications such as pancytopenia.

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HGA causing pancytopenia is likely due to a multi-modal mechanism involving immune and non-immune platelet destruction, global bone marrow suppression, hemophagocytic lymphohistiocytosis, and myelosuppressive chemokines release.

Epidemiologic, Clinical and Immunological Consequences of Co-Infections during Canine Leishmaniosis

Simple Summary

Canine leishmaniosis (CanL), the most severe, visceralizing form of disease caused by Leishmania infantum transmitted by phlebotomine sand flies. CanL is frequently diagnosed in the Mediterranean basin and South America, although it is also found in other regions, including the United States (U.S.). Dogs in these regions are at risk for co-infections, prominently tick-borne diseases. Our review examines epidemiologic, clinical, and immunologic mechanisms found during the most common eight CanL co-infections reported in published literature. Co-infections alter immunologic processes and disease progression impacting CanL diagnosis, therapeutic responses, and prognosis.

Abstract

Canine leishmaniosis (CanL) is a vector-borne, parasitic disease. CanL is endemic in the Mediterranean basin and South America but also found in Northern Africa, Asia, and the U.S. Regions with both competent sand fly vectors and L. infantum parasites are also endemic for additional infectious diseases that could cause co-infections in dogs. Growing evidence indicates that co-infections can impact immunologic responses and thus the clinical course of both CanL and the comorbid disease(s). The aim for this review is to summarize epidemiologic, clinical, and immunologic factors contributing to eight primary co-infections reported with CanL: Ehrlichia spp., Anaplasma spp., Borrelia spp., Babesia spp., Trypanosoma cruzi, Toxoplasma gondii, Dirofilaria immitis, Paracoccidioides braziliensis. Co-infection causes mechanistic differences in immunity which can alter diagnostics, therapeutic management, and prognosis of dogs with CanL. More research is needed to further explore immunomodulation during CanL co-infection(s) and their clinical impact.

Human Granulocytic Anaplasmosis presenting as Subacute Abdominal Pain and Hyponatremia

Human Granulocytic Anaplasmosis (HGA) is an acute febrile tick-borne illness caused by the organism Anaplasma phagocytophilum. Patients often present with fever and a flu-like symptoms following a tick bite. In this case, the patient presented with subacute abdominal pain and severe hyponatremia consistent with SIADH. The patient was started on appropriate empiric antibiotics given the patient’s tick exposure. Blood smear confirmed findings consistent with HGA and the patient continued antibiotic treatment with resolution of his symptoms. This case is unique in that the patient presented with severe hyponatremia that improved with treatment of the HGA. He also had subacute abdominal pain which is also a rare presentation of HGA. Our hope is that our case highlights the value of empiric treatment with appropriate monitoring to prevent downstream, severe sequelae from undiagnosed HGA. In the setting of climate change, increased duration of Ixodes spp. tick life cycles with emerging regional distribution of the ticks, coinfections with Borrelia burgdorferi and increased incidence of HGA in the last two decades, it is important to recognize this entity.

Acquired aplastic anemia: Is bystander insult to autologous hematopoiesis driven by immune surveillance against malignant cells?

We previously reported a serendipitous finding from a patient with refractory severe aplastic anemia who had gotten an unexpected hematological response to treatment with gut-cleansing preparations (GCPs). This patient experienced three recurrences over the ensuing one year of intermittent GCP treatments, with each recurrence occurring 7-8 wk from a GCP. After his third recurrence, he was prescribed successive treatment with rifampicin, berberine, and monthly administered GCP for 4 mo, and he developed an erythroid proliferative neoplasma and an overwhelming enteropathy, and eventually died of septic shock. Laboratory investigations had validated the resolution of myelosuppression and the appearance of malignant clonal hematopoiesis. From the treatment process and laboratory investigations, it is reasonably inferred that the engagement of gut inflammation is critically required in sustaining the overall pathophysiology of acquired aplastic anemia probably by creating a chronic inflammatory state. Incorporation of rifampicin, berberine, and monthly GCP into cyclosporine can enhance the immunosuppressive effect. In a subgroup of acquired aplastic anemia patients whose pathogenesis is associated with genotoxic exposure, the suppressed normal hematopoiesis may result from the bystander insult that is mediated by the soluble inflammatory cytokines generated in response to the immunogenic products of damaged hematopoietic cells in the context of chronic inflammatory state and may offer a protective antineoplastic mechanism against malignant proliferation.

Equine Granulocytic Anaplasmosis, A Neglected Disease: Risk Factors Associated with Prevalence of Antibodies in Equines

Background:

Anaplasma phagocytophilum, a tick-borne bacterium that causes granulocytic anaplasmosis, is a neglected pathogen in Brazil, and is diagnosed in several species of domestic and wild animals as well as in humans.

Objective:

This study aimed to investigate the prevalence of anti-A. phagocytophilum antibodies in Equidae from the state of Rio de Janeiro and to identify possible risk factors for infection.

Materials and Methods:

A total of 612 blood samples were collected from horses from 15 municipalities within the state. Moreover, an epidemiological questionnaire was administered to evaluate aspects related to seroreaction, taking into account the spatial distribution (properties, municipalities, and mesoregions), management practices, signs of disease, and the individual state of the animals. For the diagnosis, indirect immunofluorescence was performed.

Results:

In the present study, 124 (20.26%), out of a total of 612, animals with anti-A. phagocytophilum IgG antibodies at titers of 1:80 were detected. Multivariate logistic regression analysis showed that the presence of the infection at the property (P <0.0001) and the origin (P = 0.0095) of the horse were the true risk factors for infection in the state of Rio de Janeiro.

Conclusion:

This allows to infer that the bacterium is distributed in all mesoregions of the state of Rio de Janeiro and that animals from other states can introduce the infection and make a property a focus of disease; it can also be inferred that these properties are important in the maintenance of the disease and the permanence of bacteria circulating in horses. It is also noteworthy that this was the first identification of mules as hosts of A. phagocytophilum infection.

Innate Immune Response to Tick-Borne Pathogens: Cellular and Molecular Mechanisms Induced in the Hosts

Many pathogens are transmitted by tick bites, including Anaplasma spp., Ehrlichia spp., Rickettsia spp., Babesia and Theileria sensu stricto species. These pathogens cause infectious diseases both in animals and humans. Different types of immune effector mechanisms could be induced in hosts by these microorganisms, triggered either directly by pathogen-derived antigens or indirectly by molecules released by host cells binding to these antigens. The components of innate immunity, such as natural killer cells, complement proteins, macrophages, dendritic cells and tumor necrosis factor alpha, cause a rapid and intense protection for the acute phase of infectious diseases. Moreover, the onset of a pro-inflammatory state occurs upon the activation of the inflammasome, a protein scaffold with a key-role in host defense mechanism, regulating the action of caspase-1 and the maturation of interleukin-1β and IL-18 into bioactive molecules. During the infection caused by different microbial agents, very similar profiles of the human innate immune response are observed including secretion of IL-1α, IL-8, and IFN-α, and suppression of superoxide dismutase, IL-1Ra and IL-17A release. Innate immunity is activated immediately after the infection and inflammasome-mediated changes in the pro-inflammatory cytokines at systemic and intracellular levels can be detected as early as on days 2–5 after tick bite. The ongoing research field of “inflammasome biology” focuses on the interactions among molecules and cells of innate immune response that could be responsible for triggering a protective adaptive immunity. The knowledge of the innate immunity mechanisms, as well as the new targets of investigation arising by bioinformatics analysis, could lead to the development of new methods of emergency diagnosis and prevention of tick-borne infections.

Myeloid Cells Restrict MCMV and Drive Stress-Induced Extramedullary Hematopoiesis through STAT1

Cytomegalovirus (CMV) has a high prevalence worldwide, is often fatal for immunocompromised patients, and causes bone marrow suppression. Deficiency of signal transducer and activator of transcription 1 (STAT1) results in severely impaired antiviral immunity. We have used cell-type restricted deletion of Stat1 to determine the importance of myeloid cell activity for the defense against murine CMV (MCMV). We show that myeloid STAT1 limits MCMV burden and infection-associated pathology in the spleen but does not affect ultimate clearance of infection. Unexpectedly, we found an essential role of myeloid STAT1 in the induction of extramedullary hematopoiesis (EMH). The EMH-promoting function of STAT1 was not restricted to MCMV infection but was also observed during CpG oligodeoxynucleotide-induced sterile inflammation. Collectively, we provide genetic evidence that signaling through STAT1 in myeloid cells is required to restrict MCMV at early time points post-infection and to induce compensatory hematopoiesis in the spleen.

Exploring Phenotypes for Disease Resilience in Pigs Using Complete Blood Count Data From a Natural Disease Challenge Model

Disease resilience is a valuable trait to help manage infectious diseases in livestock. It is anticipated that improved disease resilience will sustainably increase production efficiency, as resilient animals maintain their performance in the face of infection. The objective of this study was to identify phenotypes related to disease resilience using complete blood count (CBC) data from a wean-to-finish natural disease challenge model, established to mimic the disease pressure caused by many common pathogens at the commercial level of pig production. In total, 2433 F1 crossbred (Landrace × Yorkshire) barrows that went through the natural disease challenge model were classified into four groups (resilient, average, susceptible, and dead) based on their divergent responses in terms of growth and individual treatment. Three sets of blood samples for CBC analysis were drawn at 2-weeks before, and at 2- and 6-weeks after the challenge: Blood 1, Blood 3, and Blood 4 respectively. CBC of Blood 1 taken from healthy pigs before challenge did not show differences between groups. However, resilient animals were found to be primed to initiate a faster adaptive immune response and recover earlier following infection, with greater increases of lymphocyte concentration from Blood 1 to Blood 3 and for hemoglobin concentration and hematocrit from Blood 3 to Blood 4, but a lower neutrophil concentration from Blood 3 to Blood 4 than in susceptible and dead animals (FDR < 0.05). The CBC traits in response to the challenge were found to be heritable and genetically correlated with growth and treatment, which may indicate the potential for developing CBC under disease or commercial conditions as a phenotype in commercial systems as part of developing predictions for disease resilience.

Candida/Staphylococcal Polymicrobial Intra-Abdominal Infection: Pathogenesis and Perspectives for a Novel Form of Trained Innate Immunity

Polymicrobial sepsis is difficult to diagnose and treat and causes significant morbidity and mortality, especially when fungi are involved. In vitro, synergism between Candida albicans and various bacterial species has been described for many years. Our laboratory has developed a murine model of polymicrobial intra-abdominal infection with Candida albicans and Staphylococcus aureus, demonstrating that polymicrobial infections cause high levels of mortality, while monoinfections do not. By contrast, closely related Candida dubliniensis does not cause synergistic lethality and rather provides protection against lethal polymicrobial infection. This protection is thought to be driven by a novel form of trained innate immunity mediated by myeloid-derived suppressor cells (MDSCs), which we are proposing to call "trained tolerogenic immunity". MDSC accumulation has been described in patients with sepsis, as well as in in vivo sepsis models. However, clinically, MDSCs are considered detrimental in sepsis, while their role in in vivo models differs depending on the sepsis model and timing. In this review, we will discuss the role of MDSCs in sepsis and infection and summarize our perspectives on their development and function in the spectrum of trained innate immune protection against fungal-bacterial sepsis.

Differential Susceptibility of Male Versus Female Laboratory Mice to Anaplasma phagocytophilum Infection

Human granulocytic anaplasmosis (HGA) is a debilitating, non-specific febrile illness caused by the granulocytotropic obligate intracellular bacterium called Anaplasma phagocytophilum. Surveillance studies indicate a higher prevalence of HGA in male versus female patients. Whether this discrepancy correlates with differential susceptibility of males and females to A. phagocytophilum infection is unknown. Laboratory mice have long been used to study granulocytic anaplasmosis. Yet, sex as a biological variable (SABV) in this model has not been evaluated. In this paper, groups of male and female C57Bl/6 mice that had been infected with A. phagocytophilum were assessed for the bacterial DNA load in the peripheral blood, the percentage of neutrophils harboring bacterial inclusions called morulae, and splenomegaly. Infected male mice exhibited as much as a 1.85-fold increase in the number of infected neutrophils, which is up to a 1.88-fold increase in the A. phagocytophilum DNA load, and a significant increase in spleen size when compared to infected female mice. The propensity of male mice to develop a higher level of A. phagocytophilum infection is relevant for studies utilizing the mouse model. This stresses the importance of including SABV and aligns with the observed higher incidence of infection in male versus female patients.

Pro-inflammatory immune responses are associated with clinical signs and symptoms of human anaplasmosis

Human anaplasmosis (HA) is an emerging tick-borne disease that may present as a mild flu-like illness or a life threatening, sepsis-like condition. Although disease severity is hypothesized to relate to immunopathology and immune dysfunction in humans, studies to directly measure immune responses in infected humans have been very limited. We quantified cytokines in 80 confirmed HA patients using a multiplex chemiluminescence immunoassay system and compared similarly measured responses in 1000 control subjects. Pro-inflammatory cytokines were significantly elevated in HA patients (all seven p<0.0001). Interferon gamma (IFN-γ) concentrations were particularly high, with average concentrations 7.8 times higher in the HA patients than the controls. A subset of cytokines consisting of IL-1β, IL-8, IL-6, TNF-α, and IL-10 was also coordinately high and significantly associated with severity of thrombocytopenia in HA patients. Patients with infections in the very acute stage (≤ 4 days ill) tended to have the highest IFN-γ, IL-12p70, and IL-2 levels. Higher concentrations of IL-13 and IL-5 were associated with diarrhea and vomiting. Our findings support a pathophysiological role for a pro-inflammatory response in HA, especially with regard to the modulation of hematopoiesis and subsequent hematopoietic complications.

Influence of Genetic Background on Hematologic and Histopathologic Alterations during Acute Granulocytic Anaplasmosis in 129/SvEv and C57BL/6J Mice Lacking Type I and Type II Interferon Signaling

The role of host type I IFN signaling and its interaction with other immune pathways during bacterial infections is incompletely understood. Type II IFN signaling plays a key role during numerous bacterial infections including granulocytic anaplasmosis (GA) caused by Anaplasma phagocytophilum infection. The function of combined type I and type II IFN signaling and their potential synergism during GA and similar tick-borne diseases is a topic of current research investigation. The goal of this study was to evaluate 2 mouse models of absent type I/type II IFN signaling in experimental A. phagocytophilum infection to determine the effects of background strain. Mice lacking both type I and type II IFN receptor signaling (IFNAR-/-/IFNGR-/-) on either the 129/SvEv or C57BL/6J genetic background were evaluated at days 0, 6, 8, and 12 of infection. Pathogen burden in multiple organs was largely similar between strains of infected mice, with few significant differences. Background strain influenced the immune response to infection. Mice of the 129/SvEv strain developed more severe hematologic abnormalities, particularly more severe leukocytosis with marked neutrophilia and lymphocytosis, throughout acute infection. Histopathologic changes occurred in infected mice of both strains and varied in severity by organ. 129/SvEv mice developed more severe pathologic changes in spleen and bone marrow, whereas C57BL/6J mice developed more severe renal pathology. This work highlights the importance of mouse background strain in dictating pathophysiologic response to infection and informs future work regarding the loss of type I and type II IFN signaling on the immune response during GA.

Microbe-Induced Inflammatory Signals Triggering Acquired Bone Marrow Failure Syndromes

Acquired bone marrow failure syndromes encompass a unique set of disorders characterized by a reduction in the effective production of mature cells by the bone marrow (BM). In the majority of cases, these syndromes are the result of the immune-mediated destruction of hematopoietic stem cells or their progenitors at various stages of differentiation. Microbial infection has also been associated with hematopoietic stem cell injury and may lead to associated transient or persistent BM failure, and recent evidence has highlighted the potential impact of commensal microbes and their metabolites on hematopoiesis. We summarize the interactions between microorganisms and the host immune system and emphasize how they may impact the development of acquired BM failure.

Mobilisation and dysfunction of haematopoietic stem/progenitor cells after Listonella anguillarum infection in ayu, Plecoglossus altivelis

Haematopoietic stem/progenitor cells (HSPCs) can mobilise into blood and produce immune cell lineages following stress. However, the homeostasis and function of HSPCs after infection in teleosts are less well known. Here, we report that Listonella anguillarum infection enhances HSPC mobilisation and reduces their differentiation into myeloid cells in ayu (Plecoglossus altivelis), an aquacultured teleost in East Asia. We established a colony-forming unit culture (CFU-C) assay to measure HSPCs using conditioned medium from peripheral blood mononuclear cells stimulated with phytohaemagglutinin. The number of CFU-Cs decreased in the head kidney and increased in the blood and spleen of ayu infected with L. anguillarum. HSPC mobilisation after L. anguillarum infection was mediated by norepinephrine. Furthermore, HSPCs from ayu treated with L. anguillarum lipopolysaccharide (LPS) showed defective myeloid differentiation and could no longer rescue L. anguillarum-infected ayu. HSPC expansion was suppressed after L. anguillarum infection or its LPS treatment in vitro. These results reveal a link between HSPC regulation and pathogen infection in teleosts.

Exercise as an Adjuvant Therapy for Hematopoietic Stem Cell Mobilization

Hematopoietic stem cell transplant (HSCT) using mobilized peripheral blood hematopoietic stem cells (HSPCs) is the only curative strategy for many patients suffering from hematological malignancies. HSPC collection protocols rely on pharmacological agents to mobilize HSPCs to peripheral blood. Limitations including variable donor responses and long dosing protocols merit further investigations into adjuvant therapies to enhance the efficiency of HSPCs collection. Exercise, a safe and feasible intervention in patients undergoing HSCT, has been previously shown to robustly stimulate HSPC mobilization from the bone marrow. Exercise-induced HSPC mobilization is transient limiting its current clinical potential. Thus, a deeper investigation of the mechanisms responsible for exercise-induced HSPC mobilization and the factors responsible for removal of HSPCs from circulation following exercise is warranted. The present review will describe current research on exercise and HSPC mobilization, outline the potential mechanisms responsible for exercise-induced HSPC mobilization, and highlight potential sites for HSPC homing following exercise. We also outline current barriers to the implementation of exercise as an adjuvant therapy for HSPC mobilization and suggest potential strategies to overcome these barriers.

Acute exercise mobilizes hematopoietic stem and progenitor cells and alters the mesenchymal stromal cell secretome

Transplantation of hematopoietic stem and progenitor cells (HSPC), collected from peripheral blood, is the primary treatment for many hematological malignancies; however, variable collection efficacy with current protocols merits further examination into factors responsible for HSPC mobilization. HSPCs primarily reside within the bone marrow and are regulated by mesenchymal stromal cells (MSC). Exercise potently and transiently mobilizes HSPCs from the bone marrow into peripheral circulation. Thus the purpose of the present study was to evaluate potential factors in the bone marrow responsible for HSPC mobilization, investigate potential sites of HSPC homing, and assess changes in bone marrow cell populations following exercise. An acute exercise bout increased circulating HSPCs at 15 min (88%, P < 0.001) that returned to baseline at 60 min. Gene expression for HSPC homing factors (CXCL12, vascular endothelial growth factor-a, and angiopoietin-1) were increased at 15 min in skeletal muscle and HSPC content was increased in the spleen 48 h postexercise (45%, P < 0.01). Acute exercise did not alter HSPCs or MSCs quantity in the bone marrow; however, proliferation of HSPCs (40%, P < 0.001), multipotent progenitors (40%, P < 0.001), short-term hematopoietic stem cells (61%, P < 0.001), long-term hematopoietic stem cells (55%, P = 0.002), and MSCs (20%, P = 0.01) increased postexercise. Acute exercise increased the content of the mobilization agent granulocyte-colony stimulating factor, as well as stem cell factor, interleukin-3, and thrombopoeitin in conditioned media collected from bone marrow stromal cells 15 min postexercise. These findings suggest that the MSC secretome is responsible for HSPC mobilization and proliferation; concurrently, HSPCs are homing to extramedullary sites following exercise.

Patho-epigenetics of Infectious Diseases Caused by Intracellular Bacteria

In multicellular eukaryotes including plants, animals and humans, epigenetic reprogramming may play a role in the pathogenesis of a wide variety of diseases. Recent studies revealed that in addition to viruses, pathogenic bacteria are also capable to dysregulate the epigenetic machinery of their target cells. In this chapter we focus on epigenetic alterations induced by bacteria infecting humans. Most of them are obligate or facultative intracellular bacteria that produce either bacterial toxins and surface proteins targeting the host cell membrane, or synthesise effector proteins entering the host cell nucleus. These bacterial products typically elicit histone modifications, i.e. alter the "histone code". Bacterial pathogens are capable to induce alterations of host cell DNA methylation patterns, too. Such changes in the host cell epigenotype and gene expression pattern may hinder the antibacterial immune response and create favourable conditions for bacterial colonization, growth, or spread. Epigenetic dysregulation mediated by bacterial products may also facilitate the production of inflammatory cytokines and other inflammatory mediators affecting the epigenotype of their target cells. Such indirect epigenetic changes as well as direct interference with the epigenetic machinery of the host cells may contribute to the initiation and progression of malignant tumors associated with distinct bacterial infections.

Extramedullary hematopoiesis (EMH) in laboratory animals: offering an insight into stem cell research

Extramedullary hematopoiesis (EMH) is a pathological process secondary to underlying bone marrow (BM) insufficiency in adults. It is characterized by the emergence of multipotent hematopoietic progenitors scattered around the affected tissue, most likely in the spleen, liver, and lymph node, etc. EMH in patients frequently receives less medical attention and is neglected unless a compressive or obstructive hematopoietic mass appears to endanger the patient's life. However, on a biological basis, EMH reflects the alteration of relationships among hematopoietic stem and progenitor cells (HSPCs) and their original and new microenvironments. The ability of hematopoietic stem cells (HSCs) to mobilize from the bone marrow and to accommodate and function in extramedullary tissues is rather complicated and far from our current understanding. Fortunately, many reports from the studies of drugs and genetics using animals have incidentally found EMH to be involved. Thereby, the molecular basis of EMH could further be elucidated from those animals after cross-comparison. A deeper understanding of the extramedullary hematopoietic niche could help expand stem cells in vitro and establish a better treatment in patients for stem cell transplantation.

Infection mobilizes hematopoietic stem cells through cooperative NOD-like receptor and Toll-like receptor signaling

Adult hematopoietic stem cells (HSCs) are maintained in specialized niches within the bone marrow under steady-state conditions and mobilize for extramedullary hematopoiesis during periods of stress such as bacterial infections. However, the underlying mechanisms are unclear. We show that systemic infection of mice with Escherichia coli, commonly associated with bacteremia in humans, mobilizes functional HSCs to the spleen. Accumulation of splenic HSCs (CD150+CD48-Lin(-/low)Sca1+cKit+) was diminished in TLR4-deficient and RIPK2-deficient mice, implicating TLRs and cytosolic NOD1/NOD2 signaling in the process. Accordingly, dual stimulation of NOD1 and TLR4 in radio-resistant cells alone was sufficient to mobilize HSCs, while TLR4 expression on HSCs was dispensable. Mechanistically, TLR4 and NOD1 synergistically induced granulocyte colony-stimulating factor (G-CSF), which was required for extramedullary HSC accumulation. Mobilized HSCs and progenitor cells gave rise to neutrophils and monocytes and contributed to limiting secondary infection.

Digital cell quantification identifies global immune cell dynamics during influenza infection

Hundreds of immune cell types work in coordination to maintain tissue homeostasis. Upon infection, dramatic changes occur with the localization, migration, and proliferation of the immune cells to first alert the body of the danger, confine it to limit spreading, and finally extinguish the threat and bring the tissue back to homeostasis. Since current technologies can follow the dynamics of only a limited number of cell types, we have yet to grasp the full complexity of global in vivo cell dynamics in normal developmental processes and disease. Here, we devise a computational method, digital cell quantification (DCQ), which combines genome‐wide gene expression data with an immune cell compendium to infer in vivo changes in the quantities of 213 immune cell subpopulations. DCQ was applied to study global immune cell dynamics in mice lungs at ten time points during 7 days of flu infection. We find dramatic changes in quantities of 70 immune cell types, including various innate, adaptive, and progenitor immune cells. We focus on the previously unreported dynamics of four immune dendritic cell subtypes and suggest a specific role for CD103⁺CD11b⁻DCs in early stages of disease and CD8⁺pDC in late stages of flu infection.

Anaplasma phagocytophilum: deceptively simple or simply deceptive?

Anaplasma phagocytophilum is an obligate intracellular rickettsial pathogen transmitted by ixodid ticks. This bacterium colonizes myeloid and nonmyeloid cells and causes human granulocytic anaplasmosis--an important immunopathological vector-borne disease in the USA, Europe and Asia. Recent studies uncovered novel insights into the mechanisms of A. phagocytophilum pathogenesis and immunity. Here, we provide an overview of the underlying events by which the immune system responds to A. phagocytophilum infection, how this pathogen counteracts host immunity and the contribution of the tick vector for microbial transmission. We also discuss current scientific gaps in the knowledge of A. phagocytophilum biology for the purpose of exchanging research perspectives.

Anaplasma phagocytophilum dihydrolipoamide dehydrogenase 1 affects host-derived immunopathology during microbial colonization

Anaplasma phagocytophilum is a tick-borne rickettsial pathogen that provokes an acute inflammatory response during mammalian infection. The illness caused by A. phagocytophilum, human granulocytic anaplasmosis, occurs irrespective of pathogen load and results instead from host-derived immunopathology. Thus, characterizing A. phagocytophilum genes that affect the inflammatory process is critical for understanding disease etiology. By using an A. phagocytophilum Himar1 transposon mutant library, we showed that a single transposon insertion into the A. phagocytophilum dihydrolipoamide dehydrogenase 1 gene (lpda1 [APH_0065]) affects inflammation during infection. A. phagocytophilum lacking lpda1 revealed enlargement of the spleen, increased splenic extramedullary hematopoiesis, and altered clinicopathological abnormalities during mammalian colonization. Furthermore, LPDA1-derived immunopathology was independent of neutrophil infection and correlated with enhanced reactive oxygen species from NADPH oxidase and nuclear factor (NF)-κB signaling in macrophages. Taken together, these findings suggest the presence of different signaling pathways in neutrophils and macrophages during A. phagocytophilum invasion and highlight the importance of LPDA1 as an immunopathological molecule.

Hematopoietic stem and progenitor cells as effectors in innate immunity

Recent research has shed light on novel functions of hematopoietic stem and progenitor cells (HSPC). While they are critical for maintenance and replenishment of blood cells in the bone marrow, these cells are not limited to the bone marrow compartment and function beyond their role in hematopoiesis. HSPC can leave bone marrow and circulate in peripheral blood and lymph, a process often manipulated therapeutically for the purpose of transplantation. Additionally, these cells preferentially home to extramedullary sites of inflammation where they can differentiate to more mature effector cells. HSPC are susceptible to various pathogens, though they may participate in the innate immune response without being directly infected. They express pattern recognition receptors for detection of endogenous and exogenous danger-associated molecular patterns and respond not only by the formation of daughter cells but can themselves secrete powerful cytokines. This paper summarizes the functional and phenotypic characterization of HSPC, their niche within and outside of the bone marrow, and what is known regarding their role in the innate immune response.

Hematopoiesis sculpted by pathogens: Toll-like receptors and inflammatory mediators directly activate stem cells

Hematopoietic stem cells (HSCs) repopulate the immune system during normal replenishment as well as under the burden of pathogen stress, but the respective outcomes of differentiation are not the same. Under homeostatic conditions such as those which accompany turnover of immune cell subsets, HSCs appear to co-equally prime genes associated with the major downstream lineages: lymphoid, myeloid, and megakaryocyte/erythroid. Recent studies reveal, however, that during pathogen exposure, hematopoiesis may yield progeny in proportions different than those produced under homeostasis. At least some of these effects may be due to pathogen engagement of Toll-like receptors (TLRs) expressed on HSCs. HSCs are also responsive to inflammatory cytokines that are produced in response to pathogen burden and are present in the bone marrow microenvironment. Thus, hematopoiesis is not a formulaic process that produces the same, predictable outcome regardless of the specific environmental context. Rather, hematopoiesis represents a dynamic biological system that can be appreciably responsive to environmental factors, an influence that extends to the level of the HSC itself. Knowledge of functional consequences of TLR ligation on HSCs may be therapeutically exploited and applied to treatment of hematopoietic insufficiency in the setting of infection and disease.

Downregulation of CXCL12 signaling and altered hematopoietic stem and progenitor cell trafficking in a murine model of acute Anaplasma phagocytophilum infection

Infection with a variety of bacterial pathogens results in hematopoietic stem and progenitor cell (HSPC) mobilization. The mechanism and kinetics of HSPC mobilization during infection are largely unknown. Previously, we found altered HSPC activity in bone marrow, spleen and blood during infection with Anaplasma phagocytophilum, the agent of granulocytic anaplasmosis. We hypothesized that altered CXCL12/CXCR4 signaling, a central pathway for HSPC homing to, and retention within, the bone marrow, plays a role in infection-induced alterations in HSPC number and trafficking. Mice were infected with A. phagocytophilum. Lineage-cKit+ HSPCs were enumerated and proliferation determined. CXCL12 and CXCR4 mRNA were quantified along with CXCL12 protein, and CXCR4 surface, intracellular and total protein expression in HSPCs was determined. Increased bone marrow proliferation of HSPCs began at 2 d post-infection followed by HSPC mobilization and splenic homing. Proliferation of resident HSPCs contributed to increased splenic HSPC numbers. Bone marrow CXCL12 mRNA and protein levels were decreased at 4-8 d post-infection concurrent with HSPC mobilization. CXCR4 protein parameters were decreased in bone marrow HSPCs throughout 2-6 d post-infection. Reduction of CXCL12/CXCR4 signaling simultaneously occurs with HSPC mobilization from bone marrow. Findings suggest that deranged CXCL12/CXCR4 signaling plays a causal role in HSPC mobilization during acute A. phagocytophilum infection.

Mechanisms of obligatory intracellular infection with Anaplasma phagocytophilum

Anaplasma phagocytophilum persists in nature by cycling between mammals and ticks. Human infection by the bite of an infected tick leads to a potentially fatal emerging disease called human granulocytic anaplasmosis. A. phagocytophilum is an obligatory intracellular bacterium that replicates inside mammalian granulocytes and the salivary gland and midgut cells of ticks. A. phagocytophilum evolved the remarkable ability to hijack the regulatory system of host cells. A. phagocytophilum alters vesicular traffic to create an intracellular membrane-bound compartment that allows replication in seclusion from lysosomes. The bacterium downregulates or actively inhibits a number of innate immune responses of mammalian host cells, and it upregulates cellular cholesterol uptake to acquire cholesterol for survival. It also upregulates several genes critical for the infection of ticks, and it prolongs tick survival at freezing temperatures. Several host factors that exacerbate infection have been identified, including interleukin-8 (IL-8) and cholesterol. Host factors that overcome infection include IL-12 and gamma interferon (IFN-γ). Two bacterial type IV secretion effectors and several bacterial proteins that associate with inclusion membranes have been identified. An understanding of the molecular mechanisms underlying A. phagocytophilum infection will foster the development of creative ideas to prevent or treat this emerging tick-borne disease.

Anaplasmosis in two dogs in France and molecular and phylogenetic characterization of Anaplasma phagocytophilum

Two dogs in France were diagnosed with Anaplasma phagocytophilum infection by real-time PCR. The most remarkable hematologic and biochemical findings were severe thrombocytopenia, mild neutrophilia, morulae in neutrophils, and increased serum concentration of the α2-globulin fraction detected by agarose gel electrophoresis of serum proteins. Using sequencing of the partial 16S rRNA and ankA genes, molecular characterization of the A. phagocytophilum strains showed that the organisms from both dogs were identical to the European strains isolated from horses and people. Based on phylogenetic analysis, the ankA gene was more discriminating than the 16S rRNA gene in distinguishing the majority of European and American strains of A. phagocytophilum infecting people and animals. Three isolates of A. phagocytophilum, 1 from Spain (cow) and 2 from Norway (sheep and deer), were external to the European and American clades.

Inflammatory signals regulate hematopoietic stem cells

Hematopoietic stem cells (HSCs) are the progenitors of all blood and immune cells, yet their role in immunity is not well understood. Most studies have focused on the ability of committed lymphoid and myeloid precursors to replenish immune cells during infection. Recent studies, however, have indicated that HSCs also proliferate in response to systemic infection and replenish effector immune cells. Inflammatory signaling molecules including interferons, tumor necrosis factor-α and Toll-like receptors are essential to the HSC response. Observing the biology of HSCs through the lens of infection and inflammation has led to the discovery of an array of immune-mediators that serve crucial roles in HSC regulation and function.

Species interactions in a parasite community drive infection risk in a wildlife population

Most hosts, including humans, are simultaneously or sequentially infected with several parasites. A key question is whether patterns of coinfection arise because infection by one parasite species affects susceptibility to others or because of inherent differences between hosts. We used time-series data from individual hosts in natural populations to analyze patterns of infection risk for a microparasite community, detecting large positive and negative effects of other infections. Patterns remain once variations in host susceptibility and exposure are accounted for. Indeed, effects are typically of greater magnitude, and explain more variation in infection risk, than the effects associated with host and environmental factors more commonly considered in disease studies. We highlight the danger of mistaken inference when considering parasite species in isolation rather than parasite communities.

Neutrophils exposed to A. phagocytophilum under shear stress fail to fully activate, polarize, and transmigrate across inflamed endothelium

Anaplasma phagocytophilum is an obligate intracellular bacterium that has evolved mechanisms to hijack polymorphonuclear neutrophil (PMN) receptors and signaling pathways to bind, infect, and multiply within the host cell. E-selectin is upregulated during inflammation and is a requisite endothelial receptor that supports PMN capture, rolling, and activation of integrin-mediated arrest. Ligands expressed by PMN that mediate binding to endothelium via E-selectin include sialyl Lewis x (sLe(x))-expressing ligands such as P-selectin glycoprotein ligand-1 (PSGL-1) and other glycolipids and glycoproteins. As A. phagocytophilum is capable of binding to sLe(x)-expressing ligands expressed on PMN, we hypothesized that acute bacterial adhesion to PMN would subsequently attenuate PMN recruitment during inflammation. We assessed the dynamics of PMN recruitment and migration under shear flow in the presence of a wild-type strain of A. phagocytophilum and compared it with a strain of bacteria that binds to PMN independent of PSGL-1. Acute bacterial engagement with PMN resulted in transient PMN arrest and minimal PMN polarization. Although the wild-type pathogen also signaled activation of beta2 integrins and elicited a mild intracellular calcium flux, downstream signals including PMN transmigration and phosphorylation of p38 mitogen-activated protein kinase (MAPK) were inhibited. The mutant strain bound less well to PMN and failed to activate beta2 integrins and induce a calcium flux but did result in decreased PMN arrest and polarization that may have been partially mediated by a suppression of p38 MAPK activation. This model suggests that A. phagocytophilum binding to PMN under shear flow during recruitment to inflamed endothelium interferes with normal tethering via E-selectin and navigational signaling of transendothelial migration.

Diminished hematopoietic activity associated with alterations in innate and adaptive immunity in a mouse model of human monocytic ehrlichiosis

Human monocytic ehrlichiosis (HME) is a tick-borne disease caused by Ehrlichia chaffeensis. Patients exhibit diagnostically important hematological changes, including anemia and thrombocytopenia, although the basis of the abnormalities is unknown. To begin to understand these changes, we used a mouse model of ehrlichiosis to determine whether the observed hematological changes induced by infection are associated with altered hematopoietic activity. Infection with Ehrlichia muris, a pathogen closely related to E. chaffeensis, resulted in anemia, thrombocytopenia, and a marked reduction in bone marrow cellularity. CFU assays, conducted on days 10 and 15 postinfection, revealed a striking decrease in multipotential myeloid and erythroid progenitors. These changes were accompanied by an increase in the frequency of immature granulocytes in the bone marrow and a decrease in the frequency of B lymphocytes. Equally striking changes were observed in spleen cellularity and architecture, and infected mice exhibited extensive extramedullary hematopoiesis. Splenomegaly, a characteristic feature of E. muris infection, was associated with an expanded and disorganized marginal zone and a nearly 66-fold increase in the level of Ter119(+) erythroid cells, indicative of splenic erythropoiesis. We hypothesize that inflammation associated with ehrlichia infection suppresses bone marrow function, induces the emigration of B cells, and establishes hematopoietic activity in the spleen. We propose that these changes, which may be essential for providing the innate and acquired immune cells to fight infection, are also responsible in part for blood cytopenias and other clinical features of HME.