gammadelta(+) T-Lp6phocyte cytotoxicity against envelope-expressing target cells is unique to the alymphocytic state of bovine leukemia virus infection in the natural host

Comparative Analysis of Maternal Colostrum and Colostrum Replacer Effects on Immunity, Growth, and Health of Japanese Black Calves

Maternal colostrum (MC) is an important source of nutrients and immune factors for newborn calves. However, when colostrum is unavailable or of poor quality, a colostrum replacer (CR) may be a suitable alternative to MC. As stock-raising farmers must make informed decisions about colostrum feeding management, this study was conducted to determine the effect of feeding MC versus CR on the promotion of immunological status, growth, and health in pre-weaned Japanese black (JB) calves. Sixteen newborn JB calves were fed MC after birth, and 16 JB calves were fed CR. For the MC group, the numbers of γδ T cells, CD4+ cells, CD8+ cells, CD4+CD8+ cells, B cells, and MHC class II+ cells were significantly higher compared with the CR group. Furthermore, the expression levels of interleukin (IL)-1β-, IL-2-, and interferon-γ (IFN-γ)-encoding mRNAs were significantly higher in the MC group compared with the CR group. A lower incidence of disease in 1-month-old calves and higher carcass weight in the MC group were observed compared with the CR group. These results suggest that CR activates the immune system delayed in calves compared with MC. MC increases populations of various immunocompetent cells, which can reduce infection rates and improve body weight gain.

Advantages and Challenges of Differential Immune Cell Count Determination in Blood and Milk for Monitoring the Health and Well-Being of Dairy Cows

A key challenge of the 21st century will be to provide the growing world population with a sustainable and secure supply of food. Consequently, the dairy farming’s primary task is to lower milk losses and other inefficiencies associated with diseased cows. Moreover, a shift from curative to preventive health management would be desirable for mastitis and a wide variety of other infectious and non-infectious cattle diseases, some of which are known to have profound negative effects on the performance and well-being of cows. Differential cell counting (DCC), a procedure that aims to determine the proportions of different somatic cell types in raw milk samples, has not only the potential to optimize mastitis diagnostics, but it could furthermore serve as a diagnostic tool for monitoring the general and overall health status of dairy cows. Based on a broad search of the literature, the practical utility of various types of DCC is summarized and discussed in this review. Since it might be of advantage to interpret DCC with the aid of data from studies in humans, differences between the immune systems of humans and dairy cattle, with a special focus on surface marker expression profiles and γδ (gamma delta) T-cell characteristics, are also described.

Lymphocyte proliferation and apoptosis of lymphocyte subpopulations in bovine leukemia virus-infected dairy cows with high and low proviral load

Bovine leukemia virus (BLV) is one of the most important virus in dairy cattle. The infection behavior follows what we call the iceberg phenomenon: 60% of infected animals do not show clinical signs; 30% develop persistent lymphocytosis (PL); and the remaining 10%, die due to lymphosarcoma. BLV transmission depends on infected cell exchange and thus, proviral load is determinant. Understanding the mechanisms by which cattle governs the control of viral dissemination will be desirable for designing effective therapeutic or preventive strategies for BLV. The development of high proviral load (HPL) or low proviral load (LPL) might be associated to genetic factors and humoral immune responses, however cellular responses are not fully described. It is known that BLV affects cellular homeostasis: proliferation and apoptosis. It is also known that the BLV tropism is directed towards B lymphocytes, and that lymphocytotic animals have elevated amounts of these cells. Usually, when an animal is infected by BLV, the B markers that increase are CD21, CD5 and CD11b. This increase could be related to the modulation of apoptosis in these cells. This is the first work in which animals infected with BLV are classified according to their proviral load and the subpopulations of B and T lymphocytes are evaluated in terms of their percentage in peripheral blood and its stage of apoptosis and viability. PBMCs from HPL animals proliferated more than LPL and non-infected animals. CD11b⁺/CD5⁺ lymphocytes in LPL animals presented greater early and late apoptosis than HPL animals and cells of HPL animals had increased viability than LPL animals. Our results confirm that BLV alters the mechanism of apoptosis and proliferation of infected cells.

Genome-wide scan for commons SNPs affecting bovine leukemia virus infection level in dairy cattle

BACKGROUND

Bovine leukemia virus (BLV) infection is omnipresent in dairy herds causing direct economic losses due to trade restrictions and lymphosarcoma-related deaths. Milk production drops and increase in the culling rate are also relevant and usually neglected. The BLV provirus persists throughout a lifetime and an inter-individual variation is observed in the level of infection (LI) in vivo. High LI is strongly correlated with disease progression and BLV transmission among herd mates. In a context of high prevalence, classical control strategies are economically prohibitive. Alternatively, host genomics studies aiming to dissect loci associated with LI are potentially useful tools for genetic selection programs tending to abrogate the viral spreading. The LI was measured through the proviral load (PVL) set-point and white blood cells (WBC) counts. The goals of this work were to gain insight into the contribution of SNPs (bovine 50KSNP panel) on LI variability and to identify genomics regions underlying this trait.

RESULTS

We quantified anti-p24 response and total leukocytes count in peripheral blood from 1800 cows and used these to select 800 individuals with extreme phenotypes in WBCs and PVL. Two case-control genomic association studies using linear mixed models (LMMs) considering population stratification were performed. The proportion of the variance captured by all QC-passed SNPs represented 0.63 (SE ± 0.14) of the phenotypic variance for PVL and 0.56 (SE ± 0.15) for WBCs. Overall, significant associations (Bonferroni's corrected -log10p > 5.94) were shared for both phenotypes by 24 SNPs within the Bovine MHC. Founder haplotypes were used to measure the linkage disequilibrium (LD) extent (r2 = 0.22 ± 0.27 at inter-SNP distance of 25-50 kb). The SNPs and LD blocks indicated genes potentially associated with LI in infected cows: i.e. relevant immune response related genes (DQA1, DRB3, BOLA-A, LTA, LTB, TNF, IER3, GRP111, CRISP1), several genes involved in cell cytoskeletal reorganization (CD2AP, PKHD1, FLOT1, TUBB5) and modelling of the extracellular matrix (TRAM2, TNXB). Host transcription factors (TFs) were also highlighted (TFAP2D; ABT1, GCM1, PRRC2A).

CONCLUSIONS

Data obtained represent a step forward to understand the biology of BLV-bovine interaction, and provide genetic information potentially applicable to selective breeding programs.

Anti-Bovine Programmed Death-1 Rat-Bovine Chimeric Antibody for Immunotherapy of Bovine Leukemia Virus Infection in Cattle

Blockade of immunoinhibitory molecules, such as programmed death-1 (PD-1)/PD-ligand 1 (PD-L1), is a promising strategy for reinvigorating exhausted T cells and preventing disease progression in a variety of chronic infections. Application of this therapeutic strategy to cattle requires bovinized chimeric antibody targeting immunoinhibitory molecules. In this study, anti-bovine PD-1 rat–bovine chimeric monoclonal antibody 5D2 (Boch5D2) was constructed with mammalian expression systems, and its biochemical function and antiviral effect were characterized in vitro and in vivo using cattle infected with bovine leukemia virus (BLV). Purified Boch5D2 was capable of detecting bovine PD-1 molecules expressed on cell membranes in flow cytometric analysis. In particular, Biacore analysis determined that the binding affinity of Boch5D2 to bovine PD-1 protein was similar to that of the original anti-bovine PD-1 rat monoclonal antibody 5D2. Boch5D2 was also capable of blocking PD-1/PD-L1 binding at the same level as 5D2. The immunomodulatory and therapeutic effects of Boch5D2 were evaluated by in vivo administration of the antibody to a BLV-infected calf. Inoculated Boch5D2 was sustained in the serum for a longer period. Boch5D2 inoculation resulted in activation of the proliferation of BLV-specific CD4⁺ T cells and decrease in the proviral load of BLV in the peripheral blood. This study demonstrates that Boch5D2 retains an equivalent biochemical function to that of the original antibody 5D2 and is a candidate therapeutic agent for regulating antiviral immune response in vivo. Clinical efficacy of PD-1/PD-L1 blockade awaits further experimentation with a large number of animals.

Cytokine profiles of dendritic cells (DCs) during infection with bovine leukaemia virus (BLV)

BLV is an agent of enzootic bovine leukaemia (EBL), an infectious disease affecting cattle worldwide. BLV infection has been associated with immune system disorders and discrepancies in the cytokine network. The significance of dendritic cells in the pathogenesis of BLV infection is largely unknown, but considering their fundamental role in immune response it may be crucial. DCs precursors were isolated with the use of immunomagnetic beads from BLV-infected and BLV-free cows. From these precursors cultures of monocyte derived dendritic cells (MoDCs) were generated with the use of a cytokine cocktail (IL-4 and GM-CSF). Additionally, parallel DCs from BLV-negative animals were infected in vitro. The level of cytokines: IL-6, IL-10, IL-12(p40), IL-12(p70) was determined in DC cultures: infected in vitro, originating from naturally infected cattle and BLV-free cattle. The investigation showed significant changes in almost all analyzed populations of BLV-infected DCs. Cytokine profiles of blood MoDCs indicated activation of these groups during infection. In the case of spleen MoDCs and lymph node MoDCs a decrease in production of IL-12(p40) and IL-12(p70) in favour of IL-6 and IL-10 was noted, suggesting promotion of BLV infection development.

Reduced humoral immunity and atypical cell-mediated immunity in response to vaccination in cows naturally infected with bovine leukemia virus

Bovine leukemia virus (BLV) is a retrovirus that is widely distributed across US dairy herds: over 83% of herds are BLV-infected and within-herd infection rates can approach 50%. BLV infection reduces both animal longevity and milk production and can interfere with normal immune health. With such a high prevalence of BLV infection in dairy herds, it is essential to understand the circumstances by which BLV negatively affects the immune system of infected cattle. To address this question, BLV- and BLV+ adult, lactating Holstein dairy cows were vaccinated with Bovi-Shield GOLD^® FP^® 5 L5 HB and their immune response to vaccination was measured over the course of 28days. On day 0 prior to vaccination and days 7, 14 and 28 post-vaccination, fresh PBMCs were characterized for T and B cell ratios in the periphery. Plasma was collected to measure titers of IgM, IgG1 and IgG2 produced against bovine herpesvirus 1 (BHV1), Leptospira hardjo and L. pomona, as well as to characterize neutralizing antibody titers produced against BHV1 and bovine viral diarrhea virus types 1 and 2. On day 18 post-vaccination, PBMCs were cultured in the presence of BHV1 and flow cytometry was used to determine IFNγ production by CD4+, CD8+ and γδ T cells and to investigate CD25 and MHCII expression on B cells. BLV+ cows produced significantly lower titers of IgM against BHV1, L. hardjo and L. pomona and produced lower titers of IgG2 against BHV1. γδ T cells from BLV+ cows displayed a hyper reactive response to stimulation in vitro, although no differences were observed in CD4+ or CD8+ T cell activation. Finally, B cells from BLV+ cows exhibited higher CD25 expression and reduced MHCII expression in response to stimulation in vitro. All together, data from this study support the hypothesis that BLV+ cows fail to respond to vaccination as strongly as BLV- cows and, consequently, may have reduced protective immunity when compared to healthy BLV- cows.

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.

Comparative biology of γδ T cell function in humans, mice, and domestic animals

γδ T cells are a functionally heterogeneous population and contribute to many early immune responses. The majority of their activity is described in humans and mice, but the immune systems of all jawed vertebrates include the γδ T cell lineage. Although some aspects of γδ T cells vary between species, critical roles in early immune responses are often conserved. Common features of γδ T cells include innate receptor expression, antigen presentation, cytotoxicity, and cytokine production. Herein we compare studies describing these conserved γδ T cell functions and other, potentially unique, functions. γδ T cells are well documented for their potential immunotherapeutic properties; however, these proposed therapies are often focused on human diseases and the mouse models thereof. This review consolidates some of these studies with those in other animals to provide a consensus for the current understanding of γδ T cell function across species.

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.

Natural killer cell number and phenotype in bovine peripheral blood is influenced by age

Natural killer (NK) cells are critical to the innate defence against intracellular infection. High NK cell frequencies have been detected in human neonates, which may compensate for the relative immaturity of the specific immune response. Additionally, phenotypic subsets of NK cells have been identified in humans with different functional properties. In this study, we examined the age distribution and phenotype of NK populations in bovine peripheral blood, including neonatal animals. We found that the NK cell populations defined by the phenotypes CD3(-)CD2(+) and NKp46(+) largely overlapped, so that the majority of NK cells in bovine peripheral blood were CD3(-)CD2(+)NKp46(+). The remainder of the NK-like cells comprised two minor populations, CD3(-)CD2(+)NKp46(-) and CD3(-)CD2(-)NKp46(+); the relative proportions of these varied with age. The lowest frequency of NK cells was recorded in 1-day-old calves, with the highest frequency in day 0 calves. The phenotypic characteristics of CD3(-)CD2(+) and NKp46(+) NK populations were similar; both populations expressed CD45RO, CD45RB, CD11b, CC84, CD8alphaalpha and CD8alphabeta and did not express CD21, WC1, CD14 or gammadelta TCR. Age-related phenotypic differences were apparent. The phenotypic characteristics of three NK subpopulations were described; a significantly greater proportion of the CD3(-)CD2(-)NKp46(+) population expressed CD8alpha compared to CD3(-)CD2(+)NKp46(+) cells. Furthermore, a significantly greater proportion of the CD3(-)CD2(+)NKp46(-) population expressed CD8 compared to total CD3(-)CD2(+) cells. Adult cattle had a significantly higher proportion of perforin(+) cells compared to calves aged </=6 weeks. In this age group, the majority of perforin(+) cells expressed NKp46, while in adults the majority of perforin(+) cells were NKp46(-). However, the proportion of NKp46(+) and CD3(-)CD2(+) cells that expressed perforin was not significantly different in any age group tested.

Alterations in CD4+, CD8+, Vgamma3, Vgammadelta, and/or Valpha betaT-lymphocyte expression in lymphoid tissues of progeny after in utero exposure to benzo(alpha)pyrene

That benzo alpha)pyrene (Balpha P) decreases both humoral and cell-mediated immunity, and leads to increases in progeny tumor development after in utero insult, suggests that T- and B-lymphocytes are made defective in exposed offspring. In the study here, C3H mice were injected once with Balpha P (150 microg/g BW) at day 12 of pregnancy and progeny lymphoid tissues were excised during gestation (day 18; GD18) or at 1 or 6 weeks post-partum. The isolated lymphoid cells were analyzed by flow cytometry/immunofluorescence or assessed for function. In Balpha P-exposed fetuses, thymic Thy1(+) cell levels were decreased (relative to levels in organs of corn oil-exposed dam progeny). In addition, for up to 6 weeks post-birth, CD4(+)CD8(+) (double positive; DP) cells were virtually absent and levels of CD4(-)CD8(-) (double negative; DN) cells were consistently at epsilon 90%. With regard to single positive (SP) cells, CD4(+) cell levels were also decreased in tissues at GD18 up through 6 weeks post-birth; CD8(+) cell levels were increased, but only in pups at 1-week and 6-weeks post-birth. In 1-week-old progeny, spleen CD8(+) cell levels were quantitatively unchanged, though CD4(+) levels were reduced 2-4-fold and CD4(-)CD8(-) DN levels significantly increased. With respect to TCRs, fetal levels of thymic CD3Vgamma(3)(+) and CD3Vgamma delta(+) cells were decreased; levels of CD3Valphabeta cells were only slightly depressed. The latter results contrast sharply with a strong reduction in CD3Valphabeta cells in the fetal livers of Balpha P-exposed progeny. Interestingly, these livers also strongly evidenced a presence of BalphaP-7,8-dihydrodiol-9,10-epoxide metabolite. When assessed for any change in function, the CD4(+), Thy1(+) cells isolated from Balpha P-exposed progeny tissues responded weakly (relative to controls) to ConA and in an allogeneic MLR. Taken in totality, the results here strengthen our original hypothesis that BalphaP can create a favorable milieu for tumor growth progression in progeny of exposed mothers by affecting development of sufficient numbers of functional lymphocytes in the offspring.

Mechanisms of leukemogenesis induced by bovine leukemia virus: prospects for novel anti-retroviral therapies in human

In 1871, the observation of yellowish nodules in the enlarged spleen of a cow was considered to be the first reported case of bovine leukemia. The etiological agent of this lymphoproliferative disease, bovine leukemia virus (BLV), belongs to the deltaretrovirus genus which also includes the related human T-lymphotropic virus type 1 (HTLV-1). This review summarizes current knowledge of this viral system, which is important as a model for leukemogenesis. Recently, the BLV model has also cast light onto novel prospects for therapies of HTLV induced diseases, for which no satisfactory treatment exists so far.

Interferon-gamma expression associated with suppression of bovine leukemia virus at the early phase of infection in sheep

Immunological control of bovine leukemia virus (BLV)-infection has been reported as dependent on the expression balance of types 1 and 2 cytokines. In this report, mRNA expression of interferon (IFN)-gamma and interleukin (IL)-2 (type 1 cytokines), and of IL-4 and IL-10 (type 2 cytokines) were evaluated in concanavalin A-stimulated peripheral blood mononuclear cells (PBMC) from BLV-infected sheep. Despite the same dose of BLV-infection, the extent of viral propagation was markedly different between eight individual sheep by 12 weeks post infection. The virus did not propagate well in three sheep, which showed augmented mRNA expression of IFN-gamma, a strong indicator of cell-mediated immunity, immediately after BLV-infection. Among the other five sheep having more than 2% of BLV-infected cells among PBMC at 12 weeks post infection, four sheep developed B-cell leukemia or lymphoma within 2 years after infection. These observations indicate IFN-gamma expression may play an important role in the protective mechanism against BLV propagation at the early phase of the infection.

Dissemination of bovine leukemia virus-infected cells from a newly infected sheep lymph node

To investigate the early establishment of bovine leukemia virus (BLV) infection, we injected BLV-infected or mock-infected allogeneic cells into the shoulder of sheep in which an efferent lymphatic duct of the draining prescapular lymph node had been cannulated. Rare mononuclear cells acting as centers of BLV infection in culture were present within 4 to 6 days in efferent lymph and within 6 to 10 days in blood. Soon after BLV injection, immunoglobulin M+ (IgM+) and CD8+ cells increased in efferent lymph and oscillated reciprocally in frequency. CD8+ blasts increased on days 4 to 6, when infectious centers increased 100-fold in lymph. On days 6 and 7, both lymph and blood were enriched with CD8+ cells that were labeled late on day 5 with an intravenous pulse of 5-bromo-2'-deoxyuridine (BrdU). Lymph, but not blood, was enriched with BrdU+ B cells on day 7. Capsid-specific antibodies became detectable in efferent lymph on days 6 to 8 and surface glycoprotein-specific antibodies on day 9, preceding their detection in serum by 9 to 14 days. Systemic dissemination of BLV-infected cells was thus accompanied by an increase in proliferating CD8+ cells and the onset of BLV-specific antibodies in lymph. Infectious centers reached maximum frequencies of 0.2% in lymph by days 11 to 13, and then their frequencies increased by 5- to 40-fold in blood cells, suggesting that many infected blood cells do not recirculate back into lymph. Beginning on days 10 to 13, a subpopulation of B cells having high levels of surface IgM increased sharply in peripheral blood. Such cells were not present in lymph. After a day 16 pulse of BrdU, recently proliferated cells that stained intensely for surface IgM appeared in blood within 15 h. Predominantly B lymphocytes contained the viral capsid protein when lymph and blood cells were cultured briefly to allow BLV expression. However, both early in lymph and later in blood, BrdU+ B cells greatly exceeded productively infected cells, indicating that new BLV infections stimulate proliferation of two different populations of B cells.

In vivo transcription of bovine leukemia virus and bovine immunodeficiency-like virus

Cellular tropism and transcription of bovine leukemia virus (BLV) and bovine immunodeficiency-like virus (BIV) were investigated using peripheral blood mononuclear cells (PBMC) collected from a cow infected with both viruses. Each PBMC subset, purified by magnetic cell sorting, was subjected to PCR and RT-PCR for detection of their integrated proviruses and transcript mRNAs. Both BLV and BIV genomes were detected by nested PCR in CD3(+), CD4(+), CD8(+) and gammadelta T cells, B cells and monocytes. However, BLV tax transcription was only detected in B cells, and only B cells also formed BLV syncytia in CC81 cells. On the other hand, BIV transcript was detected in each subpopulation of PBMC. These results indicated that BLV can infect T cells and monocytes as well as B cells, but can be expressed by transcription only in B cells. In contrast, BIV can express its transcripts in all infected cells.

The WC1(+) gammadelta T-cell population in cattle: a possible role in resistance to intracellular infection

Intracellular infections are important in veterinary medicine and detailed understanding of the associated immune responses is needed for optimal development of strategies based on diagnosis and vaccination. It is generally accepted that cell-mediated immune responses are of greatest importance in intracellular infections and recent studies from several bovine models of infection indicate that WC1(+) gammadelta T-cells have a number of possible levels of involvement, which remain incompletely defined. Investigations of experimental infection with Mycobacterium bovis in cattle have indicated that WC1(+) gammadelta T-cells are among the first cells to accumulate at initial sites of infection, an observation which has been linked with decreased numbers of these cells in the circulation within days of infection. These WC1(+) gammadelta T-cells have been shown to respond in vitro, both to protein antigens and to non-protein, phosphate containing antigens of M. bovis and to be capable of producing IFN-gamma. Studies of M. bovis infection in calves depleted of WC1(+) gammadelta T-cells by monoclonal antibody have suggested that the presence of these cells is associated with development of a Th1-biased acquired immune response. In combination, these observations allow speculation regarding a possible role for WC1(+) gammadelta T-cells as a link between the innate and acquired immune systems which is instrumental in establishing an appropriate response.

Cattle Infected with Bovine Leukaemia Virus may not only Develop Persistent B-cell Lymphocytosis but also Persistent B-cell Lymphopenia

We investigated the distribution of B and T cells in the peripheral blood of haematologically inconspicuous (non-persistent lymphocytotic, PL-) cattle infected with the bovine leukaemia virus (BLV). Flow cytometric data were obtained from six PL- cattle and compared with six age-matched animals with persistent lymphocytosis (PL+) and five non-infected healthy controls (BLV-). In the PL- group, the percentage and number of surface immunoglobulin-positive (sIg+) B cells were significantly reduced. Whereas in BLV-cattle, about 40% of the peripheral blood lymphocytes (PBL) were sIg + and 24% were sIgM + B cells. In the PL- group, less than 20% of the PBL were sIg+ and sIgM+ B cells. Only 5% of the PBL co-expressed sIgM+ and CD5+ versus 16% in BLV-. This decrease was persistent over 3 years and predominantly affected: (i) B cells that did not express sIgM; (ii) sIgM + B cells co-expressing CD5 and CD11b; and (iii) equally both lambda- and K-type light chain B-cell subpopulations. In contrast, the number of all circulating lymphocytes, CD5- and CD11b- sIgM+ B cells and CD2+ T cells did not differ. In PL+ animals, about 75% of the PBL were sIgM+ CD5+ B cells. These cells were of polyclonal origin, as light chains of the lambda- and K-type were expressed in a ratio of 4:1 (57.7% of PBL lambda+, 14% kappa+) as in BLV- animals (33.6% of PBL lambda+, 8.7% kappa+). In PL+ cattle the absolute number of B-cells and, therefore, their relative percentage is significantly increased. For this reason, even in case of absolutely increased T-cell numbers, the relative percentage of T-cells could be lower than in normal controls. The cause for the observed B cell decrease in PL- cattle is unknown, but it can be assumed that cytotoxic T cells are involved in this B-cell lymphopenia.

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.