Kinetics of CD11b/CD18 up-regulation during infection with the agent of human granulocytic ehrlichiosis in mice

A TNF-IL-1 circuit controls Yersinia within intestinal pyogranulomas

Tumor necrosis factor (TNF) is a pleiotropic inflammatory cytokine that mediates antimicrobial defense and granuloma formation in response to infection by numerous pathogens. We previously reported that Yersinia pseudotuberculosis colonizes the intestinal mucosa and induces the recruitment of neutrophils and inflammatory monocytes into organized immune structures termed pyogranulomas (PG) that control Yersinia infection. Inflammatory monocytes are essential for the control and clearance of Yersinia within intestinal PG, but how monocytes mediate Yersinia restriction is poorly understood. Here, we demonstrate that TNF signaling in monocytes is required for bacterial containment following enteric Yersinia infection. We further show that monocyte-intrinsic TNFR1 signaling drives the production of monocyte-derived interleukin-1 (IL-1), which signals through IL-1 receptors on non-hematopoietic cells to enable PG-mediated control of intestinal Yersinia infection. Altogether, our work reveals a monocyte-intrinsic TNF-IL-1 collaborative inflammatory circuit that restricts intestinal Yersinia infection.

Temporal patterns of gene expression in response to inoculation with a virulent Anaplasma phagocytophilum strain in sheep

The aim of this study was to characterize the gene expression of host immune- and cellular responses to a Norwegian virulent strain of Anaplasma phagocytophilum, the cause of tick-borne fever in sheep. Ten sheep were intravenously inoculated with a live virulent strain of A. phagocytophilum. Clinical-, observational-, hematological data as well as bacterial load, flow cytometric cell count data from peripheral blood mononuclear cells and host's gene expression post infection was analysed. The transcriptomic data were assessed for pre-set time points over the course of 22 days following the inoculation. Briefly, all inoculated sheep responded with clinical signs of infection 3 days post inoculation and onwards with maximum bacterial load observed on day 6, consistent with tick-borne fever. On days, 3-8, the innate immune responses and effector processes such as IFN1 signaling pathways and cytokine mediated signaling pathways were observed. Several pathways associated with the adaptive immune responses, namely T-cell activation, humoral immune responses, B-cell activation, and T- and B-cell differentiation dominated on the days of 8, 10 and 14. Flow-cytometric analysis of the PBMCs showed a reduction in CD4+CD25+ cells on day 10 and 14 post-inoculation and a skewed CD4:CD8 ratio indicating a reduced activation and proliferation of CD4-T-cells. The genes of important co-stimulatory molecules such as CD28 and CD40LG, important in T- and B-cell activation and proliferation, did not significantly change or experienced downregulation throughout the study. The absence of upregulation of several co-stimulatory molecules might be one possible explanation for the low activation and proliferation of CD4-T-cells during A. phagocytophilum infection, indicating a suboptimal CD4-T-cell response. The upregulation of T-BET, EOMES and IFN-γ on days 8-14 post inoculation, indicates a favoured CD4 Th1- and CD8-response. The dynamics and interaction between CD4+CD25+ and co-stimulatory molecules such as CD28, CD80, CD40 and CD40LG during infection with A. phagocytophilum in sheep needs further investigation in the future.

Inflammatory monocytes promote granuloma control of Yersinia infection

Granulomas are organized immune cell aggregates formed in response to chronic infection or antigen persistence. The bacterial pathogen Yersinia pseudotuberculosis (Yp) blocks innate inflammatory signalling and immune defence, inducing neutrophil-rich pyogranulomas (PGs) within lymphoid tissues. Here we uncover that Yp also triggers PG formation within the murine intestinal mucosa. Mice lacking circulating monocytes fail to form defined PGs, have defects in neutrophil activation and succumb to Yp infection. Yersinia lacking virulence factors that target actin polymerization to block phagocytosis and reactive oxygen burst do not induce PGs, indicating that intestinal PGs form in response to Yp disruption of cytoskeletal dynamics. Notably, mutation of the virulence factor YopH restores PG formation and control of Yp in mice lacking circulating monocytes, demonstrating that monocytes override YopH-dependent blockade of innate immune defence. This work reveals an unappreciated site of Yersinia intestinal invasion and defines host and pathogen drivers of intestinal granuloma formation.

Anaplasma phagocytophilum Induces TLR- and MyD88-Dependent Signaling in In Vitro Generated Murine Neutrophils

Anaplasma phagocytophilum is a tick-transmitted obligate intracellular Gram-negative bacterium that replicates in neutrophils. It elicits febrile disease in humans and in animals. In a mouse model, elimination of A. phagocytophilum required CD4⁺ T cells, but was independent of IFN-γ and other classical antibacterial effector mechanisms. Further, mice deficient for immune recognition and signaling via Toll-like receptor (TLR) 2, TLR4 or MyD88 were unimpaired in pathogen control. In contrast, animals lacking adaptor molecules of Nod-like receptors (NLR) such as RIP2 or ASC showed delayed clearance of A. phagocytophilum. In the present study, we investigated the contribution of further pattern recognition receptor (PRR) pathways to the control of A. phagocytophilum in vivo. Mice deficient for the NLR NOD2 had elevated bacterial loads in the early phase of infection, but were unimpaired in pathogen elimination. In contrast, animals lacking adaptor proteins of different C-type lectin receptors (CLR) such as DAP12, Fc-receptor γ-chain (FcRγ) and SYK controlled A. phagocytophilum as efficiently as wild-type mice. Further, we investigated which PRR pathways are involved in the sensing of A. phagocytophilum by in vitro generated Hoxb8 murine neutrophils. In vitro, recognition of A. phagocytophilum by murine neutrophils was dependent on TLR- and MyD88 signaling. However, it remained intact in the absence of the NLR NOD1, NOD2 and NALP3 and of the CLR adaptor molecules DAP12 and FcRγ. From these results, we conclude that TLR rather than NLR or CLR are critical for the detection of A. phagocytophilum by neutrophils although in vivo defective TLR-signaling is compensated probably because of the redundancy of the immune system.

Flow Cytometry-Detected Immunological Markers and on Farm Recorded Parameters in Composite Cow Milk as Related to Udder Health Status

Flow cytometry is a powerful technology used in many fields of cell biology. It is also used as a routine method to count somatic cells in milk and to characterize bovine milk leukocytes. In this study, we used flow cytometry to simultaneously assess the viability, the percentage of the single subsets of leukocytes and to quantify the expression of CD11b, an immunological marker of cell activation status. Immunological markers were then related with on farm recorded parameters as milk electrical conductivity (MEC) and average milk flow rate (MFR). Composite milk samples were collected from 43 cows, nine of which had naturally infected udders and 34 of which had no infected udders. First, the milk samples were classified according to bacteriological test in positive and negative. The results showed that the negative samples to bacteriological test had: (i) significantly higher percentages of live lymphocytes; (ii) significantly lower percentages of CD11b⁺ leukocytes; (iii) significantly lower MEC and higher MFR values. Then, samples were classified in three groups according to somatic cell count (SCC): Group A (n = 15), samples with SCC ≤ 100,000 cells/mL, all negative to bacteriological analysis; Group B (n = 11), samples with 100,000 < SCC < 300,000 cells/m, with four samples positive to bacteriological analysis; Group C (n = 17), samples with SCC ≥ 300,000 cell/mL with five samples positive to bacteriological analysis. Multivariate discriminant analysis was used to verify which flow cytometry immunological markers and on farm recorded parameters could better discriminate among the different groups of SCCs. Linear discriminant analysis (LDA) indicated that 5 of the 10 parameters could best be used to reveal the differences between positive and negative samples among the considered groups of SCCs. Furthermore, the Canonical discriminant analysis (CDA) indicated that composite milk samples with different SCC and infection status were clearly separated from each other in a two-dimensional space. In conclusion, the study highlighted that: (1) the conventional flow cytometry analysis applied on milk samples is a useful tool to investigate immunological parameters as potential indicators of udder health; (2) the combined evaluation of live milk leukocytes and recorded farm parameters could be useful to assess udder health status in dairy cows. The results obtained from this pilot study on few data require new and larger trials to be confirmed.

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.

Integrin β2-Chain (CD18) Over-Expression on CD4+ T Cells and Monocytes after Ischemia/Reperfusion in Patients Undergoing Primary Percutaneous Revascularization

β2-integrin subunit (CD18) plays an essential role in leukocyte recruitment and adhesion in sites of endothelial injury. We analyzed the surface expression of CD18 on T lymphocytes and monocytes in a series of patients presenting acute coronary syndrome (ACS) who underwent primary percutaneous intervention (PCI) for coronary artery revascularization. We found that basal CD18 expression on peripheral blood-derived CD4+ (but not CD8+) T lymphocytes was significantly increased in ACS patients as compared with age-matched healthy volunteers. During primary PCI, a significant increase in CD18 molecule density was detected immediately after balloon deflation (reperfusion) on both CD4+ T cells and monocytes obtained from the right atrium (RT) as compared with basal values. These data suggest that upregulation of CD18 molecules plays an important role in local recruitment of CD4+ T cells and monocytes to the site of endothelial damage after ischemia/reperfusion, therefore being responsible, at least in part, for the inflammatory-mediated complications associated with primary PCI.

Interferon-γ-dependent control of Anaplasma phagocytophilum by murine neutrophil granulocytes

Background

Anaplasma phagocytophilum is a Gram-negative obligate intracellular bacterium that is transmitted by ticks of the Ixodes ricinus complex. It replicates in neutrophils and elicits febrile disease in humans and animals. Because of its striking tropism for neutrophils, A. phagocytophilum has been used as a model organism to study the immune response against obligate intracellular pathogens. In mice, the control of A. phagocytophilum in the early phase of infection is dependent on natural killer cell-derived interferon-γ (IFN-γ). In contrast, the final elimination strictly requires CD4⁺ T-cells. It is a matter of debate, whether neutrophils serve only as host cells or as killer cells as well.

Results

To study this, we used in vitro generated murine neutrophils with defects in major antimicrobial molecules such as NADPH-oxidase (gp91^phox−/−), myeloperoxidase (MPO^−/−) and inducible nitric oxide synthase (iNOS^−/−). However, bacterial growth in gene-deficient neutrophils was comparable to that in wild-type cells. Whereas gp91^phox and MPO expression remained unchanged, the infection led to an induction of iNOS. In neutrophils stimulated with IFN-γ, bacterial growth was significantly impaired, and iNOS was induced. However, the antibacterial effect of IFN-γ was still seen in iNOS^−/− neutrophils.

Conclusion

Thus, murine in vitro generated neutrophils stimulated with IFN-γ seem to act as killer cells by an iNOS-independent mechanism.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2274-6) contains supplementary material, which is available to authorized users.

Decreased ITGAM and FcγRIIIA mRNA expression levels in peripheral blood mononuclear cells from patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease with complex genetic predisposing factors involved. ITGAM and FCγRIIIA are two kinds of immune complex clearance molecules. The variants in ITGAM and FCγRIIIA genes have been confirmed to be associated with SLE. The aim of this study is to investigate the association of mRNA expression levels of ITGAM and FCγRIIIA with SLE. Real-time transcription-polymerase chain reaction analysis (RT-PCR) was used to determine the expression levels of ITGAM and FCγRIIIA mRNA in peripheral blood mononuclear cells (PBMC) from 60 patients with SLE and 60 healthy controls. Flow cytometry was used to measure the expression level of ITGAM and FcγRIIIA from 30 SLE patients and 30 healthy controls. The expression levels of ITGAM mRNA was significantly decreased in SLE patients compared with healthy controls (P = 0.007). Patients with arthritis had higher ITGAM mRNA level than those without arthritis (P = 0.029). The expression level of FCγRIIIA mRNA in SLE patients was significantly lower than that of healthy controls (P = 0.001). Decreased expression level of FCγRIIIA mRNA was also found in patients with LN compared with those without LN (P = 0.015). The level of ITGAM mRNA in patients with anti-SSB positive, anti-RNP positive, complement reduction and increased IgG was significantly reduced. No significant correlation was found between ITGAM and FcγRIIIA mRNA expression level in SLE patients (r = -0.019, P = 0.882). Expression of ITGAM protein in T cells, neutrophil and monocyte of SLE patients was significantly lower than healthy controls (P < 0.05). For FcγRIIIA protein expression in monocyte and NK cells, there were no significant difference between SLE patients and healthy controls (P > 0.05). The altered expression levels of ITGAM and FCγRIIIA mRNA in SLE patients and their correlations with clinical data suggest that ITGAM and FCγRIIIA may play a role in this disease.

CD11a regulates effector CD8 T cell differentiation and central memory development in response to infection with Listeria monocytogenes

β2 (CD18) integrins with α-chains CD11a, -b, -c, and -d are important adhesion molecules necessary for leukocyte migration and cellular interactions. CD18 deficiency leads to recurrent bacterial infections and poor wound healing due to reduced migration of leukocytes to inflammatory sites. CD8 T cells also upregulate CD11a, CD11b, and CD11c upon activation. However, the role these molecules play for CD8 T cells in vivo is not known. To determine the function of individual β2 integrins, we examined CD8 T cell responses to Listeria monocytogenes infection in CD11a-, CD11b-, and CD11c-deficient mice. The absence of CD11b or CD11c had no effect on the generation of antigen-specific CD8 T cells. In contrast, the magnitude of the primary CD8 T cell response in CD11a-deficient mice was significantly reduced. Moreover, the response in CD11a(-/-) mice exhibited reduced differentiation of short-lived effector cells (KLRG1(hi) CD127(lo)), although cytokine and granzyme B production levels were unaffected. Notably, CD11a deficiency resulted in greatly enhanced generation of CD62L(+) central memory cells. Surprisingly, CD8 T cells lacking CD11a mounted a robust secondary response to infection. Taken together, these findings demonstrated that CD11a expression contributes to expansion and differentiation of primary CD8 T cells but may be dispensable for secondary responses to 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.

Burkholderia pseudomallei triggers altered inflammatory profiles in a whole-blood model of type 2 diabetes-melioidosis comorbidity

Melioidosis is a potentially fatal disease caused by the bacterium Burkholderia pseudomallei. Type 2 diabetes (T2D) is the most common comorbidity associated with melioidosis. B. pseudomallei isolates from melioidosis patients with T2D are less virulent in animal models than those from patients with melioidosis and no identifiable risk factors. We developed an ex vivo whole-blood assay as a tool for comparison of early inflammatory profiles generated by T2D and nondiabetic (ND) individuals in response to a B. pseudomallei strain of low virulence. Peripheral blood from individuals with T2D, with either poorly controlled glycemia (PC-T2D [n = 6]) or well-controlled glycemia (WC-T2D [n = 8]), and healthy ND (n = 13) individuals was stimulated with B. pseudomallei. Oxidative burst, myeloperoxidase (MPO) release, expression of pathogen recognition receptors (TLR2, TLR4, and CD14), and activation markers (CD11b and HLA-DR) were measured on polymorphonuclear (PMN) leukocytes and monocytes. Concentrations of plasma inflammatory cytokine (interleukin-6 [IL-6], IL-12p70, tumor necrosis factor alpha [TNF-α], monocyte chemoattractant protein 1 [MCP-1], IL-8, IL-1β, and IL-10) were also determined. Following stimulation, oxidative burst and MPO levels were significantly elevated in blood from PC-T2D subjects compared to controls. Differences were also observed in expression of Toll-like receptor 2 (TLR2), CD14, and CD11b on phagocytes from T2D and ND individuals. Levels of IL-12p70, MCP-1, and IL-8 were significantly elevated in blood from PC-T2D subjects compared to ND individuals. Notably, differential inflammatory responses of PC-T2D, WC-T2D, and ND individuals to B. pseudomallei occur independently of bacterial load and confirm the efficacy of this model of T2D-melioidosis comorbidity as a tool for investigation of dysregulated PMN and monocyte responses to B. pseudomallei underlying susceptibility of T2D individuals to melioidosis.

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.

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.

Infection with Anaplasma phagocytophilum induces multilineage alterations in hematopoietic progenitor cells and peripheral blood cells

Infection with Anaplasma phagocytophilum, a gram-negative, lipopolysaccharide (LPS)-negative, obligate intracellular bacterium, results in multiple peripheral blood cytopenias. We hypothesized that infection with this organism would result in decreased bone marrow (BM) function and shifts in hematopoietic progenitor cells (HPCs) and lineage-committed cells in a well-established murine model of infection. HPCs and lineage-committed progenitors were enumerated in the BM and spleen during acute infection. BM cytokine production and BM CXCL12 expression were determined. Infection resulted in peripheral blood bicytopenia, marked decreases in the number of lineage-committed HPCs in the BM along with concurrent increases in the number of lineage-committed HPCs in the spleen, and a mixed, predominantly myelosuppressive BM cytokine environment. There was significant downregulation of CXCL12 in BM cells that may have been partially responsible for changes in HPC trafficking observed. Changes occurred in the absence of direct pathogen infection of BM cells. Hematopoietic lineage assessment demonstrated that there was loss of erythrocytes and B lymphocytes from the BM along with increased granulopoiesis. These changes were accompanied by splenomegaly due to lymphoid hyperplasia and increased hematopoiesis, most notably erythropoiesis. These changes largely mimic well-described inflammation and endotoxin-mediated effects on the BM and spleen; however, the numbers of peripheral blood neutrophils appear to be independently modulated as granulocytic hyperplasia does not result in neutrophilia. Our findings highlight a well-conserved series of events that we demonstrate can be instigated by an LPS-negative pathogen in the absence of an endotoxin-mediated acute proinflammatory response.

The elimination of Anaplasma phagocytophilum requires CD4+ T cells, but is independent of Th1 cytokines and a wide spectrum of effector mechanisms

Anaplasma phagocytophilum is a Gram-negative, obligate intracellular bacterium that exhibits a striking tropism for neutrophils. When we depleted mice of neutrophils, we found that murine susceptibility to anaplasmal infection was dependent on their presence. While serving as sites of bacterial replication, neutrophils do not seem to act as efficient killer cells in A. phagocytophilum infection, because mice deficient for antimicrobial effectors of neutrophils such as myeloperoxidase, granulocyte elastase, and cathepsin G were fully competent in pathogen elimination. To identify components of the immune system other than neutrophils that control A. phagocytophilum, we studied the course of infection in several gene-deficient mouse strains. IFN-gamma production by NK cells was important for initial defense, but not critical for pathogen elimination. In contrast, bacterial clearance was strictly dependent on CD4(+) T cells, but unexpectedly achieved in the absence of perforin, Fas/FasL and major Th1 cytokines such as IL-12, IFN-gamma, and MCP-1. These findings provide a novel paradigm for the control of an intracellular pathogen, which appears to be strikingly different from the CD4(+) T cell-, IL-12-, and IFN-gamma-dependent immunity to other intracellular bacteria.

Anaplasma phagocytophilum infects cells of the megakaryocytic lineage through sialylated ligands but fails to alter platelet production

Anaplasma phagocytophilum is an obligate intracellular bacterial pathogen that principally inhabits neutrophils. However, infection with A. phagocytophilum results in a moderate to marked thrombocytopenia. In host neutrophils, A. phagocytophilum uses sialylated ligands, primarily P-selectin glycoprotein ligand-1 (PSGL-1), to enter its host cell. PSGL-1 is expressed on a wide array of haematopoietic cells, including megakaryocytes. In this study, it was hypothesized that (i) cells of the megakaryocytic lineage (MEG-01 cells) would be susceptible to A. phagocytophilum infection and (ii) infection may induce alterations in platelet production contributing to infection-induced thrombocytopenia. It was found that MEG-01 cells are susceptible to infection. MEG-01 cells expressing abundant sialylated ligands were the most susceptible to infection, and the absence of sialylation, or blocking of PSGL-1, limited infection susceptibility. However, infected MEG-01 cells produced proplatelets and platelet-like particles comparable to uninfected cells. These results highlight a novel target of pathogen infection and suggest that the pathogen may utilize similar strategies to gain access to megakaryocytes. Direct pathogen modification of platelet production may not play a role in infection-induced thrombocytopenia.

Distinction between bacterial and viral infections

PURPOSE OF REVIEW

To commence proper treatment as rapidly as possible and to reduce unnecessary antibiotic treatments, timely knowledge of whether the infection is bacterial or viral in origin would be beneficial for the clinician. As a reliable prediction of the causative agent of bacterial infection is not possible based on clinical features, there is an ongoing need for sensitive and specific markers of bacterial infection.

RECENT FINDINGS

The most common differential diagnosis methods are reviewed here. It is also demonstrated that the measurement of the expression of complement receptors, particularly CR1 (CD35), on neutrophils can be a useful preliminary test to differentiate between bacterial and viral infections. In addition, a novel marker of local and systemic bacterial infections designated 'clinical infection score (CIS) point', which incorporates quantitative analysis of complement receptors on neutrophils and standard clinical laboratory data and displays 98% sensitivity and 97% specificity in distinguishing between bacterial and viral infections, is presented.

SUMMARY

We conclude that the diagnostic yield of measured individual variables in distinguishing between bacterial and viral infections increases upon combination.

Experimental infection of C3H/HeJ mice with the NY18 isolate of Anaplasma phagocytophilum

Human granulocytic anaplasmosis (HGA), an emerging disease of public health concern in many areas of the world, is caused by Anaplasma phagocytophilum. Small animal models of A phagocytophilum in laboratory mice have been developed and used to study the pathogenesis of HGA. In this study, we characterized the pathologic changes in acute infection of C3H/HeJ mice experimentally infected with the NY18 isolate of A phagocytophilum. Although no clinical signs were noted, acute infection was associated with gross splenomegaly, microscopic inflammatory lesions in the lung and liver, hyperplastic lesions on the spleen, and clinical pathology abnormalities including neutropenia and monocytosis. This study emphasizes the use of well-defined animal models as a valuable tool for the study of A phagocytophilum infections.

A flow cytometric method for determining the binding of coagulation factor X to monocytes in whole human blood

It is known that inflammation affects the coagulation pathway, but the mechanisms are not clear. Because a persistent inflammatory condition is associated with several chronic diseases, including cardiovascular disorders, there is intense interest in determining if and how chronic inflammation contributes to a hypercoagulable state. One pathway by which inflammation interacts with coagulation is via monocyte binding and activation of coagulation Factor X (FX). Upon activation, monocytes express the alphaMbeta2 integrin CD11b/CD18, which has a binding site for the plasma protein FX. Binding is followed by the cleavage of FX into its activated form Xa(FXa) which, in turn, is responsible for the conversion of prothrombin to thrombin. To assess the contribution of this pathway, a straightforward assay in whole blood is needed for studies of inflammation-induced coagulation and thrombosis. The current assay for FXa binding requires isolation of the monocytes and measurement of bound FXa activity with a chromogenic substrate. Harvesting a sufficient number of monocytes for analysis requires a relatively large blood sample. In addition, it is known that the process of isolating neutrophils and monocytes from whole blood induces an upregulation of CD11b. Thus, the measurement process itself causes an artifact in receptor expression resulting in an overestimate of true state of monocyte activation and FX binding. To address these limitations, we developed a flow cytometric assay to directly measure the binding of FX to monocytes in whole blood. In this report we describe the methods of the procedure in detail and apply the procedure to demonstrate a significant increase of both monocyte CD11b expression and FXa binding when human blood samples were activated with the endotoxin, lipopolysaccharide in-vitro.

Modulation of leukocyte populations and immune responses in sheep experimentally infected with Anaplasma (formerly Ehrlichia) phagocytophilum

Anaplasma phagocytophilum infection in sheep is characterized by an immune suppression as indicated by impaired antibody response, reduced lymphocyte response and reduced oxidative burst. The effect of A. phagocytophilum infection on leucocyte populations, especially lymphocytes, was therefore investigated in six sheep experimentally infected with A. phagocytophilum, and compared with leucocyte populations from control animals.To investigate the ability of the infection to interfere with the cellular and humoral responses to specific antigens, the animals were vaccinated with commercial vaccines at the time of experimental infection, and monitored for 56 days. There were reduced percentages of gammadelta T-cells and CD4+ T-cells in peripheral blood of infected animals throughout the study period, and these cell populations showed a down-regulation of CD25 expression; while there was a relative increase in CD8+ T-cells. The reduction in CD25+ gammadelta T-cells involved a subpopulation of WC1+ gammadelta T-cells. During the first 2 weeks of the study there were reduced percentages of B-cells and leukocytes expressing MHC II and CD11b, though this decrease changed to a relative increase later in the study. The relative reductions in leucocyte populations corresponded with the observed leucopenia during the first 3 weeks post-infection, which involved lymphocyte, neutrophil and eosinophil subsets [Vet. Immunol. Immunopathol. 86 (2002) 183]. There was a reduced expression of CD11b and CD14 on granulocytes during the first 2 weeks of the study, which corresponded with the previously reported leucopenia involving neutrophils and eosinophils. Antibody responses to vaccines, lymphocyte in vitro proliferative responses to antigens and mitogens, and in vitro IFN-gamma responses to antigens were reduced up to 4 weeks after infection.

Diminished adhesion of Anaplasma phagocytophilum-infected neutrophils to endothelial cells is associated with reduced expression of leukocyte surface selectin

Anaplasma phagocytophilum propagates within neutrophils and causes a disease marked by inflammatory tissue injury or complicated by opportunistic infections. We hypothesized that infection with A. phagocytophilum modifies the binding of neutrophils to endothelial cells and the expression of neutrophil adhesion molecules and studied these changes in vitro. Infected dimethyl sulfoxide-differentiated HL-60 cells and neutrophils showed reduced binding to cultured brain and systemic endothelial cells and lost expression of P-selectin glycoprotein ligand 1 (PSGL-1, CD162) and L-selectin (CD62L) (to 33 and 5% of control values, respectively), at a time when the levels of beta(2) integrin and immunoglobulin superfamily adhesion molecules and activation markers Mac-1 and intercellular adhesion molecule 1 increased (5 to 10 times that of the control). The loss of CD162 and CD62L expression was inhibited by EDTA, which suggests that neutrophil activation and sheddase cleavage occurred. The loss of selectin expression and the retained viability of the neutrophils persisted for at least 18 h with A. phagocytophilum infection, whereas Escherichia coli and Staphylococcus aureus rapidly killed neutrophils. The adhesion defect might increase the numbers of infected cells and their persistence in the blood prior to tick bites. However, decreased CD162 expression and poor endothelial cell binding may partly explain impaired host defenses, while simultaneous neutrophil activation may aggravate inflammation. These observations may help us to understand the modified biological responses, host inflammation, and immune response that occur with A. phagocytophilum infections.

Roles of neutrophil beta 2 integrins in kinetics of bacteremia, extravasation, and tick acquisition of Anaplasma phagocytophila in mice

Tick saliva contains anti-inflammatory and immunosuppressive substances that facilitate blood feeding and enhance tick-vectored pathogen transmission, including Anaplasma phagocytophila an etiologic agent of granulocytic ehrlichiosis. As such, inflammation at a tick-feeding site is strikingly different than that typically observed at other sites of inflammation. Up-regulation of CD11b/CD18 occurs in host granulocytes following interaction or infection with A phagocytophila, and the absence of CD11b/CD18 results in early increases in bacteremia. We hypothesized that beta 2 integrin-dependent infection kinetics and leukocyte extravasation are important determinants of neutrophil trafficking to, and pathogen acquisition at, tick-feeding sites. A phagocytophila infection kinetics were evaluated in CD11a/CD18, CD11b/CD18, and CD18 knock-out mice using quantitative polymerase chain reaction (PCR) of blood, ticks, and skin biopsies in conjunction with histopathology. A marked increase in the rate of A phagocytophila infection of neutrophils and pathogen burden in blood followed tick feeding. Infection kinetics were modified by beta 2 integrin expression and systemic neutrophil counts. Significant neutrophil-pathogen trafficking was observed to both suture and tick sites. Despite the prominent role for beta 2 integrins in neutrophil arrest in flowing blood, successful pathogen acquisition by ticks occurred in the absence of beta 2 integrins. Establishment of feeding pools that rely less on leukocyte trafficking and more on small hemorrhages may explain the ready amplification of A phagocytophila DNA from ticks infested on CD11/CD18-deficient mouse strains.