Generation and functional characterization of bovine bone marrow-derived macrophages

Pro-inflammatory capacity of Escherichia coli O104:H4 outbreak strain during colonization of intestinal epithelial cells from human and cattle

In 2011, Germany was struck by the largest outbreak of hemolytic uremic syndrome. The highly virulent E. coli O104:H4 outbreak strain LB226692 possesses a blended virulence profile combining genetic patterns of human adapted enteroaggregative E. coli (EAEC), rarely detected in animal hosts before, and enterohemorrhagic E. coli (EHEC), a subpopulation of Shiga toxin (Stx)-producing E. coli (STEC) basically adapted to the ruminant host. This study aimed at appraising the relative level of adaptation of the EAEC/EHEC hybrid strain LB226692 to humans and cattle. Adherence and invasion of the hybrid strain to intestinal (jejunal and colonic) epithelial cells (IEC) of human and bovine origin was compared to that of E. coli strains representative of different pathovars and commensal E. coli by means of light and electron microscopy and culture. Strain-specific host gene transcription profiles of selected cytokines and chemokines as well as host-induced transcription of bacterial virulence genes were assessed. The release of Stx upon host cell contact was quantified. The outbreak strain's immunomodulation was assessed by cultivating primary bovine macrophages with conditioned supernatants from IEC infection studies with E. coli, serving as model for the innate immunity of the bovine gut. The outbreak strain adhered to IEC of both, human and bovine origin. Electron microscopy of infected cells revealed the strain's particular affinity to human small IEC, in contrast to few interactions with bovine small IEC. The outbreak strain possessed a high-level of adhesive power, similar to human-associated E. coli strains and in contrast to bovine-associated STEC strains. The outbreak strain displayed a non-invasive phenotype, in contrast to some bovine-associated E. coli strains, which were invasive. The outbreak strain provoked some pro-inflammatory activity in human cells, but to a lower extent as compared to other pathotypes. In contrasts to bovine-associated E. coli strains, the outbreak strain induced marked pro-inflammatory activity when interacting with bovine host cells directly (IEC) and indirectly (macrophages). Among stx2-positive strains, the human-pathogenic strains (LB226692 and EHEC strain 86-24) released higher amounts of Stx compared to bovine-associated STEC. The findings imply that the outbreak strain is rather adapted to humans than to cattle. However, the outbreak strain's potential to colonize IEC of both host species and the rather mixed reaction patterns observed for all strains under study indicate, that even STEC strains with an unusual genotype as the EHEC O104:H4 outbreak strain, i.e. with an EAEC genetic background, may be able to conquer other reservoir hosts.

Coxiella burnetii Infects Primary Bovine Macrophages and Limits Their Host Cell Response

Although domestic ruminants have long been recognized as the main source of human Q fever, little is known about the lifestyle that the obligate intracellular Gram-negative bacterium Coxiella burnetii adopts in its animal host. Because macrophages are considered natural target cells of the pathogen, we established primary bovine monocyte-derived macrophages (MDM) as an in vitro infection model to study reservoir host-pathogen interactions at the cellular level. In addition, bovine alveolar macrophages were included to take cell type peculiarities at a host entry site into account. Cell cultures were inoculated with the virulent strain Nine Mile I (NMI; phase I) or the avirulent strain Nine Mile II (NMII; phase II). Macrophages from both sources internalized NMI and NMII. MDM were particularly permissive for NMI internalization, but NMI and NMII replicated with similar kinetics in these cells. MDM responded to inoculation with a general upregulation of Th1-related cytokines such as interleukin-1β (IL-1β), IL-12, and tumor necrosis factor alpha (TNF-α) early on (3 h postinfection). However, inflammatory responses rapidly declined when C. burnetii replication started. C. burnetii infection inhibited translation and release of IL-1β and vastly failed to stimulate increased expression of activation markers, such as CD40, CD80, CD86, and major histocompatibility complex (MHC) molecules. Such capability of limiting proinflammatory responses may help Coxiella to protect itself from clearance by the host immune system. The findings provide the first detailed insight into C. burnetii-macrophage interactions in ruminants and may serve as a basis for assessing the virulence and the host adaptation of C. burnetii strains.

Bovine macrophages sense Escherichia coli Shiga toxin 1

Shiga toxin (Stx)-producing Escherichia coli (STEC) infections in cattle are asymptomatic; however, Stx impairs the initiation of an adaptive immune response by targeting bovine peripheral and intraepithelial lymphocytes. As presumptive bovine mucosal macrophages (Mø) are also sensitive to Stx, STEC may even exert immune modulatory effects by acting on steps preceding lymphocyte activation at the Mø level. We therefore studied the expression of the Stx receptor (CD77), cellular phenotype and functions after incubation of primary bovine monocyte-derived Mø with purified Stx1. A significant portion of bovine Mø expressed CD77 on their surface, with the recombinant B-subunit of Stx1 binding to >50% of the cells. Stx1 down-regulated significantly surface expression of CD14, CD172a and co-stimulatory molecules CD80 and CD86 within 4 h of incubation, while MHC-II expression remained unaffected. Furthermore, incubation of Mø with Stx1 increased significantly numbers of transcripts for IL-4, IL-6, IL-10, IFN-γ, TNF-α, IL-8 and GRO-α but not for IL-12, TGF-β, MCP-1 and RANTES. In the course of bovine STEC infections, Stx1 appears to induce in Mø a mixed response pattern reminiscent of regulatory Mø, which may amplify the direct suppressive effect of the toxin on lymphocytes.

Evaluation of biological safety in vitro and immunogenicity in vivo of recombinant Escherichia coli Shiga toxoids as candidate vaccines in cattle

Cattle are the most important reservoir for enterohemorrhagic Escherichia coli (EHEC), a subset of shigatoxigenic E. coli (STEC) capable of causing life-threatening infectious diseases in humans. In cattle, Shiga toxins (Stx) suppress the immune system thereby promoting long-term STEC shedding. First infections of animals at calves’ age coincide with the lack of Stx-specific antibodies. We hypothesize that vaccination of calves against Shiga toxins prior to STEC infection may help to prevent the establishment of a persistent type of infection. The objectives of this study were to generate recombinant Shiga toxoids (rStx1_mut & rStx2_mut) by site-directed mutagenesis and to assess their immunomodulatory, antigenic, and immunogenic properties. Cultures of bovine primary immune cells were used as test systems. In ileal intraepithelial lymphocytes both, recombinant wild type Stx1 (rStx1_WT) and rStx2_WT significantly induced transcription of IL-4 mRNA. rStx1_WT and rStx2_WT reduced the expression of Stx-receptor CD77 (syn. Globotriaosylceramide, Gb3) on B and T cells from peripheral blood and of CD14 on monocyte-derived macrophages. At the same concentrations, rStx1_mut and rStx2_mut exhibited neither of these effects. Antibodies in sera of cattle naturally infected with STEC recognized the rStx_mut toxoids equally well as the recombinant wild type toxins. Immunization of calves with rStx1_mut plus rStx2_mut led to induction of antibodies neutralizing Stx1 and Stx2. While keeping their antigenicity and immunogenicity recombinant Shiga toxoids are devoid of the immunosuppressive properties of the corresponding wild type toxins in cattle and candidate vaccines to mitigate long-term STEC shedding by the reservoir host.

Cloning and expression of porcine Colony Stimulating Factor-1 (CSF-1) and Colony Stimulating Factor-1 Receptor (CSF-1R) and analysis of the species specificity of stimulation by CSF-1 and Interleukin 34

Macrophage Colony Stimulating Factor (CSF-1) controls the survival, differentiation and proliferation of cells of the mononuclear phagocyte system. A second ligand for the CSF-1R, Interleukin 34 (IL-34), has been described, but its physiological role is not yet known. The domestic pig provides an alternative to traditional rodent models for evaluating potential therapeutic applications of CSF-1R agonists and antagonists. To enable such studies, we cloned and expressed active pig CSF-1. To provide a bioassay, pig CSF-1R was expressed in the factor-dependent Ba/F3 cell line. On this transfected cell line, recombinant porcine CSF-1 and human CSF-1 had identical activity. Mouse CSF-1 does not interact with the human CSF-1 receptor but was active on pig. By contrast, porcine CSF-1 was active on mouse, human, cat and dog cells. IL-34 was previously shown to be species-specific, with mouse and human proteins demonstrating limited cross-species activity. The pig CSF-1R was equally responsive to both mouse and human IL-34. Based upon the published crystal structures of CSF-1/CSF-1R and IL34/CSF-1R complexes, we discuss the molecular basis for the species specificity.

Morphine enhances Tat-induced activation in murine microglia

There is increasing evidence that opiates accelerate the pathogenesis and progression of acquired immunodeficiency syndrome (AIDS), as well as the incidence of human immunodeficiency virus (HIV) encephalitis (HIVE), a condition characterized by inflammation, leukocyte infiltration, and microglial activation. The mechanisms, by which the HIV-1 transactivating protein Tat and opioids exacerbate microglial activation, however, are not fully understood. In the current study, we explored the effects of morphine and HIV-1 Tat(1-72) on the activation of mouse BV-2 microglial cells and primary mouse microglia. Both morphine and Tat exposure caused up-regulation of the chemokine receptor CCR5, an effect blocked by the opioid receptor antagonist naltrexone. Morphine in combination with Tat also induced morphological changes in the BV-2 microglia from a quiescent to an activated morphology, with a dramatic increase in the expression of the microglial activation marker CD11b, as compared with cells exposed to either agent alone. In addition, the mRNA expression of inducible nitric oxide synthase (iNOS), CD40 ligand, Interferon-gamma-inducible protein 10 (IP-10), and the proinflammatory cytokines tumor necrosis factor alpha (TNFalpha), interleukin (IL)-1beta, and IL-6, which were elevated with Tat alone, were dramatically enhanced with Tat in the presence of morphine. In summary, these findings shed light on the cooperative effects of morphine and HIV-1 Tat on both microglial activation and HIV coreceptor up-regulation, effects that could result in exacerbated neuropathogenesis.

The response of HEK293 cells transfected with bovine TLR2 to established pathogen-associated molecular patterns and to bacteria causing mastitis in cattle

Toll-like receptors (TLRs) are key sensors of pathogen-associated molecular patterns (PAMPs). Their role in immunity is difficult to examine in species of veterinary interest, due to restricted access to the knockout technology and TLR-specific antibodies. An alternative approach is to generate cell lines transfected with various TLRs and to examine the recognition of PAMPs or relevant bacteria. In this report, we examined whether recognition of various PAMPs and mastitis-causing bacteria is achieved by transfection of recombinant bovine TLR2 (boTLR2). Therefore, human embryonic kidney (HEK) 293 cells were transfected by whole boTLR2. A clonal analysis of stably transfected cells disclosed variable recognition of several putative TLR2 agonists although expressing similar amounts of the transgene and endogenous TLR6. One clone (clone 25) reacted by copious interleukin-8 (IL-8) production to several stimulants of TLR2 such as di-palmitoylated cysteyl-seryl-lysyl-lysyl-lysyl-lysine (Pam2), a biochemical preparation of lipoteichoic acid from Staphylococcus aureus, a commercial preparation of peptidoglycan from S. aureus, and heat-killed Listeria monocytogenes (HKLM). TLR2-dependent induction of IL-8 release was stronger in medium containing human serum albumin than in medium containing fetal calf serum. Clone 25 cells responded to high concentrations of S. aureus and to Escherichia coli causing mastitis, but not to Streptococcus uberis and to Streptococcus agalactiae which also cause mastitis. Stimulation by S. aureus was relatively weak when compared (i) with stimulation of the same cells by HKLM and PAMPs derived from S. aureus, (ii) with a clone stably transfected with TLR4 and MD-2 and stimulated by E. coli causing mastitis, and (iii) with interferon-gamma-costimulated bovine macrophages stimulated by S. aureus and S. agalactiae. Thus, clone 25 is suitable for studying the interaction of putative TLR2 agonists with bovine TLR2-transfected cells, provides a cell to search for TLR2-specific antibodies, and is a tool for studying the interaction of TLR2 with bacteria causing disease, e.g. mastitis, in cattle.

The microglial "activation" continuum: from innate to adaptive responses

Microglia are innate immune cells of myeloid origin that take up residence in the central nervous system (CNS) during embryogenesis. While classically regarded as macrophage-like cells, it is becoming increasingly clear that reactive microglia play more diverse roles in the CNS. Microglial "activation" is often used to refer to a single phenotype; however, in this review we consider that a continuum of microglial activation exists, with phagocytic response (innate activation) at one end and antigen presenting cell function (adaptive activation) at the other. Where activated microglia fall in this spectrum seems to be highly dependent on the type of stimulation provided. We begin by addressing the classical roles of peripheral innate immune cells including macrophages and dendritic cells, which seem to define the edges of this continuum. We then discuss various types of microglial stimulation, including Toll-like receptor engagement by pathogen-associated molecular patterns, microglial challenge with myelin epitopes or Alzheimer's β-amyloid in the presence or absence of CD40L co-stimulation, and Alzheimer disease "immunotherapy". Based on the wide spectrum of stimulus-specific microglial responses, we interpret these cells as immune cells that demonstrate remarkable plasticity following activation. This interpretation has relevance for neurodegenerative/neuroinflammatory diseases where reactive microglia play an etiological role; in particular viral/bacterial encephalitis, multiple sclerosis and Alzheimer disease.

Patterns of cellular gene expression in cells infected with cytopathic or non-cytopathic bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) infection in cattle is responsible for mucosal disease; an invariably fatal syndrome characterized by the recovery of two BVDV strains: cytopathic (cp) or noncytopathic (ncp). To understand the cellular responses to cp BVDV infection, we carried out differential display-polymerase chain reaction (DD-PCR) analysis of gene expression in infected cells. Altered expression of 14 genes involved in several functions was observed in cells infected with cp BVDV: (1) immune regulation, such as CD46, FKBP-12, and osteopontin (OPN); (2) apoptosis-related cysteine proteases like calpain; (3) signaling plasma membrane proteins such as integrin beta1, and prion protein; and (4) unknown function genes. Northern blot analysis of the expression of these genes in ncp BVDV infected cells revealed that while the expression of some genes was affected as in cp BVDV infected cells, others show a clearly contrary change. We postulate that a cause-effect relationship may exist between the differential gene expression alterations that characterize cp and ncp BVDV infections and the unique diseases associated with each BVDV biotype.

Noncytopathic bovine viral diarrhea virus inhibits double-stranded RNA-induced apoptosis and interferon synthesis

Bovine viral diarrhea virus (BVDV), a pestivirus of the Flaviviridae family, is an economically important cattle pathogen with a worldwide distribution. Both noncytopathic (ncp) and cytopathic (cp) biotypes of BVDV can be isolated from persistently infected cattle suffering from the lethal mucosal disease. The cp biotype correlates with the production of the NS3 nonstructural protein, which in the corresponding ncp biotype is present in its uncleaved form, NS23. Previously, we have shown that cp but not ncp BVDV induces the formation of alpha/beta interferons in bovine macrophages. In this study, we demonstrate that ncp BVDV inhibits the induction of apoptosis and the expression of interferon alpha/beta by poly(IC), a synthetic double-stranded RNA (dsRNA). Inhibition was observed only in cells which had been infected with ncp BVDV at least 12 h prior to the addition of dsRNA, which indicates that expression of viral proteins is necessary for the ncp virus to inhibit the effects of poly(IC). Additional experiments using transfected poly(IC) showed that ncp BVDV interfered with the intracellular action of dsRNA rather than with its uptake into the cells. Infected cells were not resistant to induction of apoptosis by actinomycin D or staurosporine, which suggests that ncp BVDV may specifically interfere with signaling through dsRNA. Interference with the innate antiviral host responses may explain the successful establishment of persistent infection by ncp BVDV in fetuses early in their development.

Bovine monocytoid cells transformed to proliferate cease to exhibit lineage-specific functions

Bovine cell lines of the monocyte-Mphi lineage were tested for surface marker expression and were characterized with respect to functions. Cell lines tested encompassed an SV40-transformed cell line (Bo-Mac), a spontaneously emerging monocytoid cell line (M617), and T. annulata-transformed lines derived from bovine Mphi. All lines failed to express surface markers expressed by 1 degrees Mphi, with the exception of CD44, WC9 and the DH59 myleoid cell marker. T. annulata-derived lines expressed, in addition, CD45 and MHC-class-II molecules. Except for nonspecific esterase staining, none of the typical macrophage functions were expressed by any of the cell lines. These included phagocytosis of opsonized E. coli bacteria and of IgG-treated erythrocytes, eliciting of an oxidative burst, the ability to express type-I-interferon (IFN) and to respond to lipopolysaccharide, as determined by four different effector functions (nitric oxide synthesis, tumor necrosis factor (TNF) secretion, IFN production and procoagulant activity upregulation). When transformation induced by T. annulata was reversed by chemical elimination of the parasite, cells ceased to proliferate but started to acquire some of the phenotypic characteristics of Mphi. This suggests that regardless of their origin, exponentially growing bovine cells of the monocyte-Mphi lineage poorly represent a lineage-specific phenotype and should be used with caution in immunological studies.

Differences Between B Cell and Macrophage Transformation by the Bovine Parasite, Theileria annulata: A Clonal Approach

Theileria annulata, a tick-transmitted protozoan parasite, infects and transforms cells of the hemopoietic system, particularly those of the B cell and monocyte/macrophage lineages. Here, the effect of infection/transformation on the resulting phenotype was studied using a clonal approach. Three phenotypes of transformed cell lines could be discerned. The first is characterized by surface expression of IgM, CD21, and the B cell epitopes, B-B2 and B-B8, Ig heavy chain gene rearrangement, and mRNA expression. Such lines were obtained from fresh and cultured PBMC and at increased frequency from purified B cells, but never from fetal bone marrow cells. The second phenotype can be distinguished from the first by the absence of Ig heavy chain expression and reduced surface expression of B cell markers (CD21, B-B2, B-B8). Clones with this phenotype were obtained from transformed fetal bone marrow cells only. The third phenotype showed an absence of all of the above B cell markers, including surface IgM, and a lack of Ig heavy chain gene rearrangement. The latter clones could be maintained for several weeks after elimination of T. annulata by BW720c treatment, and they reacquired a macrophage-like phenotype. This implies that parasite-induced dedifferentiation is restricted to monocyte/macrophage, and that B cell markers are indicative of cell lineage progeny. Demonstration of surface IgM on PBMC-derived B cell clones suggests that infection of B cells with T. annulata may be an epigenetic method to immortalize ruminant B cells of a defined Ag specificity.

Analysis of the phenotype and phagocytic activity of monocytes/macrophages from cattle infected with the bovine leukaemia virus

The bovine leukaemia virus (BLV) is a retrovirus that infects mainly B lymphocytes of cattle, but proviral DNA can also be isolated from monocytes/macrophages. This study investigated the effect of BLV infection on surface antigens on freshly isolated peripheral blood monocytes and cultured monocyte-derived macrophages, with and without lipopolysaccharide (LPS) stimulation. The effect of BLV infection on phagocytic activity of CD14+ monocytes was also assessed. The percentage of monocytes expressing the surface antigens CD11b, CD32 (FcgammaRII), MHC class II and the surface antigen recognised by mAb DH59B were increased in BLV-positive cattle. In contrast, expression intensity of all markers was low in samples from BLV-positive cattle. CD14+ monocytes from BLV-positive cattle showed less Fcgamma-receptor-mediated phagocytosis compared to monocytes from BLV-negative cattle. After 7 days in culture, there was evidence for shedding/downregulation of surface antigens on monocyte-derived macrophages, in particular on cells from BLV-positive cattle. LPS stimulation decreased the percentage of cells expressing the measured markers in monocyte-derived macrophages taken from BLV-negative cattle, but not in cultures derived from BLV-positive cattle. The results provide further evidence for an altered function of monocytes and macrophages in BLV-infected cattle.

Interferon production by Theileria annulata-transformed cell lines is restricted to the beta family

Theileria are tick-transmitted protozoans causing often fatal diseases in ruminants. Theileria sporozoites immortalize and transform host cells of haematopoietic origin. Transformation is associated with profound functional alterations. For example, bovine cells infected by Theileria annulata or T. parva. constitutively produce interferon (IFN). In this study, the type and family of IFN produced by a panel of T. annulata-transformed cell lines and a T. parva-transformed cell line was investigated, using molecular probes specific for the members of the IFN-alpha, IFN-beta, IFN-gamma and IFN-omega family. T. parva-transformed cells produced IFN-gamma exclusively, whereas T. annulata-infected cells expressed type I IFN only. Analysis of mRNA expression showed that this type I IFN was confined to IFN-beta, regardless of the cellular origin of the transformed cells. When cells were exposed to double-stranded RNA (poly (I:C)) which induces IFN production in other systems, a 10-5,000 fold increase in IFN activity was noted. The amounts of IFN-beta mRNA were increased, but mRNA coding for IFN-alpha, IFN-omega or IFN-gamma was not detected. In contrast, primary macrophages, from which many of the tested lines were derived, expressed IFN-alpha, IFN-beta and IFN-omega mRNA to similar degrees when stimulated by LPS or poly (I:C). Thus, T. annulata appears to constitutively turn on IFN-beta gene transcription while silencing the genes coding for IFN-alpha and IFN-omega.

Generation and functional characterisation of canine bone marrow-derived macrophages

A culture of bone marrow cells from the femurs of canine pups at high concentrations of fetal calf serum under non-adherent conditions allowed the proliferation and differentiation of mononuclear phagocyte lineage cells, as evidenced by morphology and CD14 expression. Cells from other lineages progressively diminished in numbers. Cells collected between 12 and 19 days of culture expressed an array of macrophage activities including ingestion of opsonised erythrocytes, generation of superoxide, up-regulation of procoagulant activity and synthesis of tumour necrosis factor (TNF) upon appropriate stimulation. TNF production was enhanced when the cultures were simultaneously stimulated with canine recombinant, or supernatant-derived, interferon-gamma. In contrast, low levels of inducible nitric oxide (NO) synthase were expressed by only a minority of stimulated macrophages, and nitrite could not be detected in the medium. Therefore, canine macrophages generated by this novel culture system resemble human macrophages in their inefficient and restricted generation of NO upon appropriate stimulation.

Comparison of inducible nitric oxide synthase expression in the brains of Listeria monocytogenes-infected cattle, sheep, and goats and in macrophages stimulated in vitro

The expression of inducible nitric oxide synthase (iNOS) was studied in the brains of cattle, sheep, and goat that succumbed to a natural infection with Listeria monocytogenes. The lesions in infected brains are characterized by microabscesses, perivascular cuffs, gliosis, glial nodules, and large areas of malacia. Using immunocytochemistry, we detected bacteria in microabscesses, particularly in sheep and goats, and in areas without signs of inflammation, but not in perivascular infiltrates. iNOS was expressed by macrophage (Mphi)-type cells of microabscesses and glial nodules but rarely by Mphi in areas of malacia, as determined by immunohistochemistry with iNOS-specific antibodies. iNOS was not detected in perivascular cuffs. Major histocompatibility complex class II molecules (MHC-II), another marker of cell activation, showed a different pattern of distribution. Perivascular cuffs contained high numbers of MHC-II-positive cells, including some with Mphi characteristics. Microabscesses in sheep and goats showed low expression of MHC-II, particularly in iNOS-expressing cells. In cattle, the expression of markers for activated or recruited phagocytes, the calcium-binding proteins S100A8 and S100A9 (formerly called MRP-8 and MRP-14, respectively), was largely restricted to cells showing weak or undetectable iNOS expression; iNOS-positive Mphi showed a low expression of S100A8 and S100A9. Thus, iNOS is expressed by a restricted subset of Mphi in listeric encephalitis. In cultured sheep and goat Mphi, a low proportion of cells expressed iNOS upon activation by L. monocytogenes and gamma interferon, resulting in nitrite generation at least 1 order of magnitude lower than that in similarly treated cattle Mphi. Since these species differences were much less obvious in vivo, it appears that the well-known species variation in iNOS expression by Mphi could reflect an in vitro phenomenon.

Serum factors, cell membrane CD14, and beta2 integrins are not required for activation of bovine macrophages by lipopolysaccharide

The role of serum factors such as lipopolysaccharide (LPS)-binding protein (LBP) and of macrophage-expressed CD14 and beta2 integrins in the activation of bovine macrophages by LPS was investigated. Macrophage activation was determined by measuring tumor necrosis factor production, NO generation, and upregulation of procoagulant activity by LPS (Escherichia coli O55:B5) at concentrations of 100 pg/ml to 100 ng/ml. The 50% effective dose for LPS was 1 order of magnitude higher than that for activating human macrophages. Macrophages were activated by LPS in the presence of serum or in the presence of albumin demonstrated to be free of LBP. The capacity to react to LPS in the absence of LBP was not due to the acquisition of LBP during a previous culture in serum. It was then established which CD14-specific antibodies block LPS binding to monocytes. Among the CD14-specific antibodies recognizing bovine mononuclear phagocytes (60bca, 3C10, My4, CAM36, VPM65, CMRF31, and TUK4), the first four blocked the binding of LPS-fluorescein isothiocyanate to bovine monocytes at low concentrations. Anti-CD14 antibodies did not block LPS-mediated activation of bovine bone marrow-derived macrophages, monocyte-derived macrophages, and alveolar macrophages. This was observed in experiments in which anti-CD14 concentrations exceeded the 50% inhibitory dose by >30-fold (3C10 and My4) or >300-fold (60bca), as defined in the binding assay described above. Monocyte-derived macrophages from an animal deficient in beta2 integrins and control macrophages were activated by similar concentrations of LPS, suggesting that beta2 integrins are not important bovine LPS receptors. Thus, in bovine macrophages, LPS recognition pathways which are independent of exogenous LBP, of membrane-expressed CD14, and of beta2 integrins may exist.

Macrophages infected with cytopathic bovine viral diarrhea virus release a factor(s) capable of priming uninfected macrophages for activation-induced apoptosis

Bovine bone marrow-derived macrophages infected with the cytopathic biotype of bovine viral diarrhea virus released an antiviral activity into the supernatant which was tentatively characterized as type I interferon because of its physicochemical properties. Such supernatants primed both infected and uninfected macrophages for decreased nitric oxide production and apoptosis in response to lipopolysaccharide. This finding strongly suggests a role of this pathway in the pathogenesis of mucosal disease, a lethal form of infection with cytopathic bovine viral diarrhea virus in which the principal lesions are located in the oral cavity and the gastrointestinal tract, which are known to contain a high concentration of endotoxin.

Inducible nitric oxide synthase of macrophages. Present knowledge and evidence for species-specific regulation

An important mechanism by which macrophages (M phi) halt the growth of and eliminate a broad array of intracellular pathogens is the production of nitric oxide (NO). NO generation is catalyzed by inducible nitric oxide synthase (iNOS) converting arginine into citrulline and NO. In murine M phi, iNOS activity is regulated largely at the transcriptional level. LPS and IFN-gamma induce iNOS, IL-4 and TGF-beta down-regulate LPS or IFN-gamma induced iNOS. In human M phi, iNOS cannot be induced by conventional activating regimes in vitro. We studied iNOS induction in ruminant monocytes and M phi from various sources (bone marrow, alveolar lavage, peripheral blood) and found that there is a species-specific and differentiation stage-dependent pattern of iNOS regulation in vitro. Notably, cattle M phi and monocytes respond to distinct signals by iNOS expression. Goat monocytes and M phi resemble human, pig and rabbit M phi in that upon treatment with conventional activating stimuli, they express less iNOS than unstimulated murine or bovine M phi and fail to generate detectable amounts of nitrite and nitrate.