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

Association between phagocytic activity of monocytes and days to conception after parturition in dairy cows when considering the hormonal and metabolic milieu

The nutritional conditions and immune status of dairy cows affect reproductive performance. This study was conducted with the aim to analyze the phagocytic activity (PA) and phagocytic capacity (PC) of circulating monocytes after the period of transition from pregnancy to lactation, to evaluate possible associations with duration of time period to conception following parturition. Results indicated PA was not associated with duration of time period to conception following parturition. In contrast, cows with a lesser PC conceived earlier (98 ± 9 days in milk, DIM) than those with a greater PC (168 ± 15 DIM). Based on these results, to analyze the association of the hormonal and metabolic milieu with the PA and PC, the animals were grouped considering the days to conception following parturition. In the group with the greater number of days to conception (>168 DIM), the PA was associated with concentrations of progesterone and beta-hydroxybutyrate (BHB) at 90 DIM and glucose at 120 DIM, whereas PC was associated with the concentrations of progesterone, cortisol and glucose at 90 DIM, non-esterified fatty acids (NEFA) at 120 DIM, 17β-estradiol at 150 DIM, and 17β-estradiol and BHB at 180 DIM. Overall, these results represent a new perspective related to the reproductive performance of dairy cows. The modifications of cellular functions may be useful for predicting the onset of health complications in dairy cows and to manage cows in ways that result in an enhanced fertility during the subsequent lactational period.

Milk Macrophage Function in Bovine Leukemia Virus-Infected Dairy Cows

The implications of bovine leukemia virus (BLV) on innate and adaptive immune responses have been widely investigated; however, the effects of BLV on mammary gland immunity require further investigation. The present study investigated the viability, phagocytic capacity, and intracellular production of reactive oxygen and nitrogen species (RONS) by macrophages in milk samples from dairy cows naturally infected with BLV with or without persistent lymphocytosis (PL). No effect of BLV infection in the overall number of macrophages per milliliter and in the percentage of viable macrophages among overall milk viable cells was found. Furthermore, BLV-infected dairy cows had a higher frequency of viable milk macrophages, while healthy animals had a tendency toward a higher percentage of apoptotic milk macrophages. The percentage of milk macrophages that phagocytosed Staphylococcus aureus in seronegative animals was higher than that in BLV-infected dairy cows. No effect of BLV infection on the intracellular RONS production and the intensity of phagocytosis by milk macrophages was observed. Thus, this study provides new insights into the implications of BLV infections in the bovine mammary gland.

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.

Heterogeneity of Bovine Peripheral Blood Monocytes

Peripheral blood monocytes of several species can be divided into different subpopulations with distinct phenotypic and functional properties. Herein, we aim at reviewing published work regarding the heterogeneity of the recently characterized bovine monocyte subsets. As the heterogeneity of human blood monocytes was widely studied and reviewed, this work focuses on comparing bovine monocyte subsets with their human counterparts regarding their phenotype, adhesion and migration properties, inflammatory and antimicrobial functions, and their ability to interact with neutrophilic granulocytes. In addition, the differentiation of monocyte subsets into functionally polarized macrophages is discussed. Regarding phenotype and distribution in blood, bovine monocyte subsets share similarities with their human counterparts. However, many functional differences exist between monocyte subsets from the two species. In contrast to their pro-inflammatory functions in human, bovine non-classical monocytes show the lowest phagocytosis and reactive oxygen species generation capacity, an absent ability to produce the pro-inflammatory cytokine IL-1β after inflammasome activation, and do not have a role in the early recruitment of neutrophils into inflamed tissues. Classical and intermediate monocytes of both species also differ in their response toward major monocyte-attracting chemokines (CCL2 and CCL5) and neutrophil degranulation products (DGP) in vitro. Such differences between homologous monocyte subsets also extend to the development of monocyte-derived macrophages under the influence of chemokines like CCL5 and neutrophil DGP. Whereas the latter induce the differentiation of M1-polarized macrophages in human, bovine monocyte-derived macrophages develop a mixed M1/M2 macrophage phenotype. Although only a few bovine clinical trials analyzed the correlation between changes in monocyte composition and disease, they suggest that functional differences between human and bovine monocyte subsets are also reflected in their different clinical relevance for distinct diseases. In opposite to the human system, where higher blood cell number of non-classical monocytes was widely correlated with several human infectious and non-infectious diseases, higher counts of bovine intermediate monocytes are suggested as a potential biomarker for inflammatory responses postpartum.

Immunological implications of bovine leukemia virus infection

This study examined neutrophil and monocyte functions and the blood lymphocyte profile of naturally BLV-infected cows with or without persistent lymphocytosis (PL). The percentage of neutrophils and monocytes that phagocytosed Staphylococcus aureus was lower in BLV-infected dairy cows, particularly those with PL. The relative percentage of CD44⁺ monocytes and neutrophils and CD11b expression by neutrophils was also lower in BLV-infected dairy cows with PL. A correlation between the percentage of CD11b⁺ neutrophils and that produced reactive oxygen species (ROS) was found. Furthermore, the percentage of CD44⁺ monocytes was positively correlated with the percentage of monocytes that phagocytosed S. aureus and the same phenomenon was observed for neutrophils. In BLV-infected dairy cows, particularly those with PL, inhibition of monocyte and neutrophil apoptosis was observed. Additionally, the percentage of neutrophils producing ROS was lower in BLV-infected cows with PL, in contrast to higher intensity of intracellular production of ROS by monocytes. The result from the lymphocyte immunophenotyping of BLV-infected cows with PL was an increase in B cells, mainly B CD5⁺ CD11b⁺, due to the apoptosis inhibition. In conclusion, this study provides novel insight into the implications of BLV infection for cattle, which can include the dysfunction of blood monocytes and neutrophils.

Bovine P-selectin mediates leukocyte adhesion and is highly polymorphic in dairy breeds

Bovine P-selectin (SELP) mediates leukocyte rolling and primes leukocyte adhesion to endothelium, both essential for leukocyte recruitment to an infection site. We investigated SELP-mediated adhesion between bovine peripheral blood leukocytes (PBLs) and cultured bovine aortic endothelial cells pre-activated with lipopolysaccharide (LPS). We examined gene polymorphism for bovine selectins SELP, l-selectin (SELL) and E-selectin (SELE) and compared their SNP frequency between five dairy breeds (Holstein, Friesian, Jersey, Ayrshire and Brown Swiss). LPS treatment caused a rapid (10min) and slower (4h) enhancement of PBL adhesion (P<0.01). Antibody blocking of SELP inhibited LPS induced cell adhesion. SELP was highly polymorphic, with 9 of the 13 SNPs in its exons, whereas only three synonymous SNPs in SELL and one in SELE. The resulting amino acid changes for the three missense SELP SNP were located in the lectin domain and in two consensus repeat (CR) regions, CR2 and CR5. The Val475Met variant locus in the CR4 and CR5 linking region was very close to a predicted N-acetyl-d-glucosamine glycosylation site, which is likely to influence SELP function. The AA genotype was under-represented, only being found in 1% of 373 heifers genotyped from the 5 breeds (P=0.056), suggesting that AA homozygous animals carrying the Val475Met substitution for SELP may have compromised development. Our study thus confirmed that SELP mediates the attachment of PBL to endothelium and provides novel evidence that its high polymorphism is likely to affect biological function. This may potentially influence leukocyte migration and fertility, both key to successful performance in dairy cows.

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.

Effect of infection with bovine leukemia virus on milk production in Michigan dairy cows

The objective of this study was to determine the association between individual cow-level milk production and bovine leukemia virus (BLV) infection as measured by milk BLV-ELISA. Dairy Herd Improvement technicians collected milk samples from 10 cows from each of first, second, third, and 4+ parity cows in 105 Holstein herds with ≥ 120 milking cows. Milk samples were tested for the presence of anti-BLV antibodies by ELISA. Additional data regarding the cows and the herds were collected by farm survey and Dairy Herd Improvement records. A set of mixed-effect models using all cows and only 2+ parity cows were used to investigate the association between BLV ELISA-corrected optical density and 305-d mature equivalents of individual cows. The BLV milk positivity was associated with decreased 305-d mature-equivalent yields, especially among the older cows. Additionally, increasing milk ELISA-corrected optical density was associated with increasing loss of milk production at the cow level. In summary, our results provide evidence that BLV infection is associated with decreased milk production in Michigan dairy cows.

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.

Bovine leukemia virus: a major silent threat to proper immune responses in cattle

Bovine leukemia virus (BLV) infection is widespread in the US dairy industry and the majority of producers do not actively try to manage or reduce BLV incidence within their herds. However, BLV is estimated to cost the dairy industry hundreds of millions of dollars annually and this is likely a conservative estimate. BLV is not thought to cause animal distress or serious pathology unless infection progresses to leukemia or lymphoma. However, a wealth of research supports the notion that BLV infection causes widespread abnormal immune function. BLV infection can impact cells of both the innate and adaptive immune system and alter proper functioning of uninfected cells. Despite strong evidence of abnormal immune signaling and functioning, little research has investigated the large-scale effects of BLV infection on host immunity and resistance to other infectious diseases. This review focuses on mechanisms of immune suppression associated with BLV infection, specifically aberrant signaling, proliferation and apoptosis, and the implications of switching from BLV latency to activation. In addition, this review will highlight underdeveloped areas of research relating to BLV infection and how it causes immune suppression.

Avaliação funcional de monócitos de bovinos naturalmente infectados pelo vírus da leucose bovina

Para a avaliação funcional de monócitos de bovinos infectados pelo vírus da leucose enzoótica bovina (LEB), foram coletadas amostras de sangue de 10 vacas com sorodiagnóstico negativo (SN), 10 com sorodiagnóstico positivo e que manifestavam linfocitose persistente (LP), e 10 com sorodiagnóstico positivo alinfocitóticas (AL). Os monócitos foram separados por gradiente de densidade e aderência em placa, submetidos aos testes de viabilidade por exclusão do azul de tripan, fagocitose de partículas de Zymosan, espraiamento em lamínula de vidro e quantificação da liberação de peróxido de hidrogênio (H2O2) e de óxido nítrico (ON). Monócitos de animais com LP apresentaram os menores índices de viabilidade (P<0,001), de fagocitose (P<0,001) e de espraiamento (P=0,006). Também apresentaram maior produção de H2O2 sem prévio estímulo (P=0,001) e após estímulo in vitro com 12-miristato 13-acetato de forbol (P=0,006) do que monócitos de animais SN e AL. O aumento da produção de H2O2 proporcionado pelo estímulo foi menor (P=0,015) nos monócitos de fêmeas que manifestaram LP. Não houve diferença na produção de ON pelos monócitos segundo os grupos. Os resultados indicam que o vírus da LEB, apesar de infectar linfócitos B, altera funcionalmente os monócitos circulantes em bovinos que manifestam LP.

The role of antigen presenting cells in multiple sclerosis

Multiple sclerosis (MS) is a debilitating T cell mediated autoimmune disease of the central nervous system (CNS). Animal models of MS, such as experimental autoimmune encephalomyelitis (EAE) and Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) have given light to cellular mechanisms involved in the initiation and progression of this organ-specific autoimmune disease. Within the CNS, antigen presenting cells (APC) such as microglia and astrocytes participate as first line defenders against infections or inflammation. However, during chronic inflammation they can participate in perpetuating the self-destructive environment by secretion of inflammatory factors and/or presentation of myelin epitopes to autoreactive T cells. Dendritic cells (DC) are also participants in the presentation of antigen to T cells, even within the CNS. While the APCs alone are not solely responsible for mediating the destruction to the myelin sheath, they are critical players in perpetuating the inflammatory milieu. This review will highlight relevant studies which have provided insight to the roles played by microglia, DCs and astrocytes in the context of CNS autoimmunity.

Functional group/guild modelling of inter-specific pathogen interactions: a potential tool for predicting the consequences of co-infection

Although co-infection is the norm in most human and animal populations, clinicians currently have no practical tool to assist them in choosing the best treatment strategy for such patients. Given the vast range of potential pathogens which may co-infect the host, obtaining such a practical tool may seem an intractable problem. In ecology the joint concepts of functional groups and guilds have been used to conceptually simplify complex ecosystems, in order to understand how their component parts interact and may be manipulated. Here we propose a mechanism by which to apply these concepts to pathogen co-infection systems. Further, we describe how these groups could be incorporated into a mathematical modelling framework which, after validation, could be used as a clinical tool to predict the outcome of any particular combination of pathogens co-infecting a host.

Long-term collection and characterization of afferent lymph from the ovine small intestine

Reliable methods for long-term collection of afferent lymph draining from the small intestine of sheep are described and validated. The procedure was used successfully in normal sheep, in animals infected experimentally with the parasitic intestinal nematode Trichostrongylus colubriformis and in animals infected naturally with Mycobacterium avium subsp. paratuberculosis, the causative agent of Johne's disease. Our approach enabled afferent lymph draining from the small intestine to be collected continuously for up to 4 months, without any detrimental effects on the animals. Based on cytokine gene expression profiles of afferent intestinal lymph cells, the two infections induced contrasting regional immune responses, namely, Th2-type immunity in the case of T. colubriformis infection and Th1-type immunity in natural cases of Johne's disease. Some immune parameters differed markedly between the two disease models, highlighting the potential value of this approach to gain real-time insights into distinctive host-pathogen interactions as they occur in vivo within the regional immune system of the gastrointestinal tract.

Lack of TNF alpha supports persistence of a plasmid encoding the bovine leukaemia virus in TNF(-/-) mice

Tumour necrosis factor (TNF) is well recognised for its role in mediating innate immune responses. However, the mechanisms of TNF that influence the adaptive immune response to viral infections are poorly understood. Over recent years, there has been evidence to suggest a role for TNF in the early phase of infection of ruminants with bovine leukaemia virus (BLV). In this study, we infected TNF(-/-) mice with a plasmid encoding infectious BLV to further elucidate the role of TNF in BLV infection. TaqMan quantitative PCR showed that proviral DNA was present in genomic DNA isolated from spleen cells of TNF(-/-) mice 4 weeks post-infection, whereas it was not detected in wild-type mice. We were not able to detect differences in serum IgM or IgG levels between the TNF(-/-) and wild-type mice, or antibodies to BLV after this short period. In showing that the lack of TNF enables the plasmid encoded BLV to persist longer, and therefore rendering the mice more susceptible to an infection with BLV, the data suggest an important defence function of TNF in the early phase of BLV infection.

Reduced IL-2 and IL-4 mRNA expression in CD4+ T cells from bovine leukemia virus-infected cows with persistent lymphocytosis

The role of T-helper (Th) responses in the subclinical progression of bovine leukemia virus (BLV) infection was explored by determining the contribution of CD4+ T cells to the expression of mRNAs encoding interferon-gamma (IFN-gamma), interleukin-2 (IL-2), interleukin-4 (IL-4), and interleukin-10 (IL-10) in BLV-infected cattle. Relative levels of mRNA encoding IFN-gamma, IL-2, IL-4, and IL-10 were measured in fresh and concanavalin A (Con A) activated peripheral blood mononuclear cells (PBMCs) and purified CD4+ T cells from cows seronegative to BLV (BLV-), seropositive without persistent lymphocytosis (BLV+PL-), and seropositive with PL (BLV+PL+) using a semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) assay. The expressions of IFN-gamma, IL-2, and IL-4 mRNAs were significantly reduced in the PBMCs from BLV+PL+ cows as compared to BLV- cows. Reduced levels of IL-2 and IL-4 mRNAs were detected in fresh CD4+ T cells from BLV+PL+ cows. In contrast, Con A stimulated PBMCs and CD4+ T cells did not differ significantly in expression of IFN-gamma, IL-2, IL-10, or IL-4 mRNAs among the BLV infection groups. Using flow-sorted CD4+ T cells and semiquantitative RT-PCR the frequencies of CD4+ T cells transcribing IFN-gamma, IL-2, IL-4, and IL-10 mRNAs in the peripheral blood of BLV-, BLV+PL-, and BLV+PL+ cows were determined. There were no significant differences in the frequencies of CD4+ T cells expressing these cytokine mRNAs among animals in the different BLV infection categories. Thus, the observed differences in IL-2 and IL-4 mRNAs in CD4+ T cells were due to changes in steady-state mRNA levels expressed by individual cells and not to changes in the frequency of cells transcribing IL-2 and IL-4 mRNAs. These results demonstrate that the progression of BLV infection to PL is associated with reduced expression of classical Th1 and Th2 cytokines by CD4+ T cells, thus suggesting aberrant Th regulation in subclinically infected animals.

Role of bovine chemokines produced by dendritic cells in respiratory syncytial virus-induced T cell proliferation

Respiratory syncytial virus (RSV) has been reported to induce the production of chemokines in the airway epithelia. Dendritic cells (DC) are the most potent antigen-presenting cells. They are located throughout the body and release chemokines in response to inflammation and infection. We have investigated the chemokine profile of bovine DC in response to exposure to bovine RSV (BRSV). Transcripts for several chemokines were detected by RT-PCR, subsequently cloned and expressed, and the products analysed by western blotting. To test the effect of the recombinant chemokines on RSV-induced T cell proliferation, DC were pulsed with BRSV, irradiated, and added to purified bovine CD4(+) T cells from RSV-immune cattle in combination with various concentrations of recombinant chemokines, and the proliferative response of the T cells assessed. Eotaxin was the only chemokine, of those investigated, that specifically enhanced the T cell response to BRSV-pulsed DC. Addition of MIP-1alpha to control wells or to wells containing BRSV-pulsed DC had similar effects, suggesting non-specific stimulation of T cells. RANTES and MIP-3alpha did not seem to influence the proliferative response of T cells co-cultured with BRSV-pulsed DC. Thus, although BRSV induced the production of several chemokines by DC, only eotaxin promoted a BRSV specific CD4(+) T cell proliferative response.

Morphologic and functional changes in bovine monocytes infected in vitro with the bovine leukaemia virus

Experiments on the host cell spectrum of bovine leukaemia virus (BLV), a retrovirus closely related to the human T-cell leukaemia virus (HTLV), have yielded conflicting data. Currently, BLV is known to infect B cells, whereas its ability to infect other cell types, e.g. monocytes/macrophages, is doubtful. As monocytes/macrophages may have profound effects on the diversity of the T-cell response, we studied the possibility of in vitro infection, using bovine monocytes and SV40-transformed bovine macrophages. Proviral DNA was detected by nested polymerase chain reaction (PCR) from day 1 until the end of the experiments at either day 5 or day 80, depending on the quantity of virus used for infection. In addition, the infection was associated with morphological changes in infected cells as revealed by electron microscopy. The in vitro infection did not significantly change either the expression of surface antigens (CD11b, CD32, and major histocompatibility complex (MHC) class II) or the amounts of cytokine transcripts (interleukin (IL)-1beta, tumour necrosis factor (TNF)-alpha, IL-6 and IL-12p40) with or without lipopolysaccharide (LPS) stimulation. The data suggest that BLV can infect monocytes, but the infection does not seem to influence the function or the phenotype of these cells. Infected monocytes may, however, play a role as a viral reservoir in vivo.

Decreased expression of L-selectin (CD62L) on lymphocytes in enzootic bovine leukaemia

Expression of L-selectin was determined by single- and two-colour immunofluorescence on granulocytes, peripheral blood mononuclear cells (PBMC) and blasts of bovine origin by means of a monoclonal antibody IVA94 which recognizes bovine L-selectin (CD62L). Cells were separated from peripheral blood of healthy cattle and colleagues infected with bovine leukaemia virus (BLV). BLV-infected animals comprised lymphocytotic and non-lymphocytotic cows. L-selectin was expressed on 90-98% of granulocytes in all tested animals. The percentage of PBMC expressing L-selectin was lower in cattle with persistent lymphocytosis than in non-lymphocytotic or BLV-free cattle, and inversely correlated with lymphocyte counts. The ratio of B lymphocytes stained for L-selectin was significantly decreased from 60.2 +/- 1.9% in BLV-free cattle to 43.8 +/- 3.6 and 22.5 +/- 5.7% in non-lymphocytotic and lymphocytotic cattle, respectively. B-lymphocytes stained for L-selectin exhibited about 50% reduction in L-selectin expression in BLV-infected cattle compared with BLV-free cattle, as judged by the mean fluorescence intensity (MFI). The percentage of L-selectin-positive PBMC not bearing surface immunoglobulin M (predominantly T lymphocytes) was comparable in BLV-free and BLV-infected cattle. However, L-selectin expression on T lymphocytes was reduced (about 50%) in BLV-infected cattle, as judged by the MFI. We suppose that BLV infection results in a decreased L-selectin expression on lymphocytes, and accordingly, it may contribute to deregulation of the host immune system.

In vitro infection of cells of the monocytic/macrophage lineage with bovine leukaemia virus

The oncogenic retrovirus bovine leukaemia virus (BLV) primarily infects B cells. Most infected animals remain asymptomatic for long periods of time before an increase in circulating B cells or localized tumours can be observed. This long clinical latency period may be explained by cells of the monocyte/macrophage lineage (M/M) becoming infected and acting as a reservoir for the virus, as shown for other retroviruses (human immunodeficiency virus-1, feline immunodeficiency virus). M/M cells in different stages of differentiation (HL-60, THP-1, U-937, J774, BGM, PM2, primary macrophages of sheep and cows) were cultured with BLV produced by permanently infected donor cells (FLKBLV and BLV-bat(2)). Donor cells were inhibited from multiplying by either irradiation or treatment with mitomycin C. In other experiments, supernatant from donor cells containing virus was used. In co-culture with the donor cells, the less differentiated monocytic cells showed severe cellular changes such as differentiation, vacuolization, cell lysis and membrane blebbing; apoptosis was a frequent phenomenon. Budding and extracellular viruses were also observed. The more differentiated macrophage cells, although they showed less signs of infection by microscopy, had a complete BLV protein profile, as seen by Western blotting; bands corresponding to p24CA (Gag) and its precursors were clearly seen. In addition, gp51SU was identified by syncytia formation assays. It is concluded that M/M cells may be infected by BLV, the consequences of the infection differing according to the type of cell.

Regulation of bovine leukemia virus tax and pol mRNA levels by interleukin-2 and -10

Recently, particular cytokines have been identified to affect progression of a variety of diseases and retrovirus infections. Previously, we demonstrated that interleukin-2 (IL-2), IL-12, and gamma interferon increased in peripheral blood mononuclear cells (PBMCs) from animals with early disease and decreased in PBMCs from animals with late disease stages of bovine leukemia virus (BLV) infection. In contrast, IL-10 increased with disease progression. To examine the effects of these cytokines on BLV expression, BLV tax and pol mRNA and p24 protein were quantified by competitive PCR and immunoblotting, respectively. IL-10 inhibited BLV tax and pol mRNA levels in BLV-infected PBMCs; however, the inhibitory effect of IL-10 was prevented in PBMCs depleted of monocytes and/or macrophages (monocyte/macrophages). To determine whether these factors were secreted or monocyte/macrophage associated, monocyte/macrophage-depleted PBMCs were cultured with isolated monocyte/macrophages in transwells where contact between monocyte/macrophages and nonadherent PBMCs was blocked. BLV tax and pol mRNA levels increased in transwell cultures similar to cultures containing nonseparated cells, and IL-10 addition inhibited the increase of BLV tax and pol mRNA. These results suggest that monocyte/macrophages secrete soluble factor(s) that increases BLV mRNA levels and that secretion of these soluble factor(s) could be inhibited by IL-10. In contrast, IL-2 increased BLV tax and pol mRNA and p24 protein production. Thus, IL-10 production by BLV-infected animals with late stage disease may serve to control BLV mRNA levels, while IL-2 may increase BLV mRNA in the early disease stage. To determine a correlation between cell proliferation and BLV expression, the effect of IL-2 and IL-10 on PBMC proliferation was tested. As anticipated, IL-2 stimulated while IL-10 suppressed antigen-specific PBMC proliferation. The present study, combined with our previous findings, suggests that increased IL-10 production in late disease stages suppresses BLV mRNA levels, while IL-2-activated immune responses stimulate BLV expression by BLV-infected B cells.