CD5 is dissociated from the B-cell receptor in B cells from bovine leukemia virus-infected, persistently lymphocytotic cattle: consequences to B-cell receptor-mediated apoptosis

B cell phenotypes and maturation states in cows naturally infected with Mycobacterium avium subsp. Paratuberculosis

Little is known about the role that B cells play in immune responses to infection with the intracellular pathogen, Mycobacterium avium subsp. paratuberculosis (MAP). Traditionally, the role of B cells has been constrained to their function as antibody-producing cells, however, antibodies are not thought to play a protective role in mycobacterial infections. The present study was designed to characterize B cell subpopulations as well as activation/maturation states in cattle with paratuberculosis. Peripheral blood mononuclear cells (PBMCs) were isolated from noninfected control cows (n = 8); as well cattle naturally infected with MAP in the subclinical (n = 8) and clinical (n = 7) stage of infection and stimulated with MAP antigen for 6 days. MAP infection resulted in greater numbers of total B cells for clinical cows compared to control noninfected cows. The major subpopulation in freshly isolated PBMCs in clinical cows was B-1a B cells, but this shifted to a composite of both B-1a and B-2 B cells upon stimulation of PBMCs with either MAP antigen or pokeweed mitogen, with higher numbers of B-2 B cells. Early B cells were observed to predominate the population of B cells in PBMCs, with lesser populations of germinal B cells, memory B cells and plasma cells. These subpopulations were elevated in clinical cows upon stimulation of PBMCs with MAP antigen, except for plasma cells which were lower compared to control noninfected cows. Increased numbers of B cells in clinical cows aligned with higher expression of B cell markers such as MAPK1/3, BTG1, Bcl2, CD79A and SWAP70, depending upon in vitro stimulation with either mitogen or antigen. This would indicate that the B cells were capable of activation but were anti-apoptotic in nature. The shift to B-2 B cells in the periphery of clinical cows seems to be indicative of an expansion of memory B cells, rather than plasma cells. This may be a last attempt by the host to control the rampant inflammatory state associated with advanced clinical disease.

Relationship of persistent lymphocytosis, antibody titers, and proviral load with expression of interleukin-12, interferon-γ, interleukin-2, interleukin-4, interleukin-10, and transforming growth factor-β in cows infected with bovine leukemia virus from a high-prevalence dairy complex

Bovine leukemia virus (BLV) subclinical infection promotes persistent lymphocytosis (PL), which is related to susceptibility and progression to lymphoma. Moreover, lymphocyte counts directly correlate with BLV antibody titers and proviral load, and cell immune responses are considered atypical due to immune suppression. In order to determine the relationship of PL, antibody titers, and proviral load with interleukin (IL)-12, interferon (IFN)-γ, IL-2, IL-4, IL-10, and transforming growth factor (TGF)-β expression in a 3-month interval, 58 cows were selected (30 BLV+ and 28 BLV-) from a high-prevalence dairy herd to complete 3 monthly blood samplings for the assessment of PL, BLV antibody titers, BLV proviral load, and IL-12, IFN-γ, IL-2, IL-4, IL-10, and TGF-β expression. At sampling conclusion, the BLV-infected cows were grouped according to PL, BLV proviral load, and BLV antibody titers as follows: BLV+PL+ (n = 16) and BLV+PL- (n = 14); high proviral load (HPL) (n = 18) and low proviral load (LPL) (n = 13); high antibody titers (HAT) (n = 17) and low antibody titers (LAT) (n = 14). The BLV+PL+ cows showed significantly higher proviral load and antibody titers than the BLV+PL- group; however, the former suggested spread presumably unrelated to lymphoma outcome, because HPL was observed in PL- cows in the last sampling. Consistent with the data, a higher antibody response strongly indicated BLV susceptibility since it was linked to PL+ occurrence and a cytokine profile compatible with immune suppression. Furthermore, a reversion to lower antibody titers was observed in cows with HPL far ahead of time, most likely due to long-term immune suppression. In addition, high expression of IL-10 and TGF-β was associated with reduced IL-12, IFN-γ, IL-2, and IL-4 expression alongside PL, HAT, and HPL in BLV-infected cows, suggesting an IL-10- and TGF-β-induced immune suppression. The IL-10 expression was increasing throughout, implying disease progression, as described. In conclusion, the proliferative expansion of lymphocytes known as PL might enhance a regulatory-rich cell population (Bregs and/or Tregs) that secretes IL-10 and TGF-β, leading to immune suppression. Further studies must be conducted regarding the types of regulatory cells involved in BLV-induced immune suppression.

Bovine Leukaemia Virus: Current Epidemiological Circumstance and Future Prospective

Bovine leukaemia virus (BLV) is a deltaretrovirus that is closely related to human T-cell leukaemia virus types 1 and 2 (HTLV-1 and -2). It causes enzootic bovine leukosis (EBL), which is the most important neoplastic disease in cattle. Most BLV-infected cattle are asymptomatic, which potentiates extremely high shedding rates of the virus in many cattle populations. Approximately 30% of them show persistent lymphocytosis that has various clinical outcomes; only a small proportion of animals (less than 5%) exhibit signs of EBL. BLV causes major economic losses in the cattle industry, especially in dairy farms. Direct costs are due to a decrease in animal productivity and in cow longevity; indirect costs are caused by restrictions that are placed on the import of animals and animal products from infected areas. Most European regions have implemented an efficient eradication programme, yet BLV prevalence remains high worldwide. Control of the disease is not feasible because there is no effective vaccine against it. Therefore, detection and early diagnosis of the disease are essential in order to diminish its spreading and the economic losses it causes. This review comprises an overview of bovine leukosis, which highlights the epidemiology of the disease, diagnostic tests that are used and effective control strategies.

[Characterization of B1-cells during experimental leukomogenesis.]

BACKGROUND

Bovine leukemia causes a significant polyclonal expansion of CD5+, IgM+ B lymphocytes, known as persistent lymphocytosis (PL), in approximately 30% of infected cattle. However, it is not yet clear what happens to this subpopulation of B cells in the early period of infection of animals.

PURPOSE

Quantitative characterization of IgM+ and CD5+ B cells during the immune response, which can provide important information on the mechanisms of lymphocyte priming in BLV infection.

MATERIAL AND METHODS

The experiment used BLV-negative calves of black-motley breed at the age of 8 months (n = 11). Animals (n = 8) were intravenously injected with blood of a BLV-positive cow. Control calves (n = 3) were injected with saline. Studies were performed before and after infection on days 5, 7, 14, 21, 28 and 65 of the immune response. The determination of the number of B-lymphocytes in the blood was carried out by the method of immunoperoxidase staining based on monoclonal antibodies to IgM, CD5.

RESULTS

As a result of the studies, it was found that the level of CD5+ B cells increases on the 14th day of the primary immune response, characterized by polyclonal proliferation of CD5+ B cells, which are the primary target for BLV. Our research data confirm that in the lymphocytes of experimentally infected cattle, surface aggregation of IgM and CD5 molecules on B-lymphocytes is absent.

DISCUSSION

It is known that the wave-like nature of IgM synthesis, which was shown in previous studies, depends on a subpopulation of B1 cells. After 7 days of the immune response, IgM+ and CD5+ cells do not correlate, which shows their functional difference. The increase in CD5+ cells is probably not associated with B cells, but with T cells differentiating under the influence of the virus.

CONCLUSIONS

A subset of B1 cells is the primary target of cattle leukemia virus. The 65th day of the immune response is characterized by the expansion of IgM+ B cells, a decrease in the number of CD5+ cells and a uniform distribution of receptors around the perimeter of the cells.

Reduced CD5 on CD8+ T Cells in Tumors but Not Lymphoid Organs Is Associated With Increased Activation and Effector Function

CD5, a member of the scavenger receptor cysteine-rich superfamily, is a marker for T cells and a subset of B cells (B1a). CD5 associates with T-cell and B-cell receptors and increased CD5 is an indication of B cell activation. In tumor-infiltrating lymphocytes (TILs) isolated from lung cancer patients, CD5 levels were negatively correlated with anti-tumor activity and tumor‐mediated activation-induced T cell death, suggesting that CD5 could impair activation of anti-tumor T cells. We determined CD5 levels in T cell subsets in different organs in mice bearing syngeneic 4T1 breast tumor homografts and assessed the relationship between CD5 and increased T cell activation and effector function by flow cytometry. We report that T cell CD5 levels were higher in CD4⁺ T cells than in CD8⁺ T cells in 4T1 tumor-bearing mice, and that high CD5 levels on CD4⁺ T cells were maintained in peripheral organs (spleen and lymph nodes). However, both CD4⁺ and CD8⁺ T cells recruited to tumors had reduced CD5 compared to CD4⁺ and CD8⁺ T cells in peripheral organs. In addition, CD5^high/CD4⁺ T cells and CD5^high/CD8⁺ T cells from peripheral organs exhibited higher levels of activation and associated effector function compared to CD5^low/CD4⁺ T cell and CD5^low/CD8⁺ T cell from the same organs. Interestingly, CD8⁺ T cells among TILs and downregulated CD5 were activated to a higher level, with concomitantly increased effector function markers, than CD8⁺/CD5^high TILs. Thus, differential CD5 levels among T cells in tumors and lymphoid organs can be associated with different levels of T cell activation and effector function, suggesting that CD5 may be a therapeutic target for immunotherapeutic activation in cancer therapy.

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 association study for host response to bovine leukemia virus in Holstein cows

The mechanisms of leukemogenesis induced by bovine leukemia virus (BLV) and the processes underlying the phenomenon of differential host response to BLV infection still remain poorly understood. The aim of the study was to screen the entire cattle genome to identify markers and candidate genes that might be involved in host response to bovine leukemia virus infection. A genome-wide association study was performed using Holstein cows naturally infected by BLV. A data set included 43 cows (BLV positive) and 30 cows (BLV negative) genotyped for 54,609 SNP markers (Illumina Bovine SNP50 BeadChip). The BLV status of cows was determined by serum ELISA, nested-PCR and hematological counts. Linear Regression Analysis with a False Discovery Rate and kinship matrix (computed on the autosomal SNPs) was calculated to find out which SNP markers significantly differentiate BLV-positive and BLV-negative cows. Nine markers reached genome-wide significance. The most significant SNPs were located on chromosomes 23 (rs41583098), 3 (rs109405425, rs110785500) and 8 (rs43564499) in close vicinity of a patatin-like phospholipase domain containing 1 (PNPLA1); adaptor-related protein complex 4, beta 1 subunit (AP4B1); tripartite motif-containing 45 (TRIM45) and cell division cycle associated 2 (CDCA2) genes, respectively. Furthermore, a list of 41 candidate genes was composed based on their proximity to significant markers (within a distance of ca. 1 Mb) and functional involvement in processes potentially underlying BLV-induced pathogenesis. In conclusion, it was demonstrated that host response to BLV infection involves nine sub-regions of the cattle genome (represented by 9 SNP markers), containing many genes which, based on the literature, could be involved to enzootic bovine leukemia progression. New group of promising candidate genes associated with the host response to BLV infection were identified and could therefore be a target for future studies. The functions of candidate genes surrounding significant SNP markers imply that there is no single regulatory process that is solely targeted by BLV infection, but rather the network of interrelated pathways is deregulated, leading to the disruption of the control of B-cell proliferation and programmed cell death.

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.

Tumor necrosis factor-alpha (TNFα) gene polymorphism and expression of membrane-bound TNFα protein on CD11b+ and IgM+ cells in cows naturally infected with bovine leukemia virus

The aim of this study was to determine whether SNP at position -824 (promoter region) of the TNFα gene significantly differentiates the size of IgM+, CD5+ and CD11b+ cell subpopulations and affects the expression of membrane-bound TNFα protein (mTNFα) on these cells and their susceptibility to BLV infections. In this study, significant differences were determined for the first time between TNFα genotypes and the percentage of cells with the CD11b+TNFα+p24+ immunophenotype. Furthermore, greater expansion of lymphocytes with the IgM+TNFα+p24+ immunophenotype was reported in cows with the G/G genotype than in A/A homozygotes. Cells with the above immunophenotype were more frequently observed in cows with persistent leukocytosis than in aleukemic cattle. Our results suggest that polymorphism of the TNFα-824 A>G gene and mTNFα protein expression play an important role in the pathogenesis of enzootic bovine leukosis.

Iron and Ferritin Levels in the Serum and Milk of Bovine Leukemia Virus-Infected Dairy Cows

Iron metabolism was examined in 15 bovine leukemia virus (BLV)-infected dairy cows (2.6–7.8 years old). BLV infection was detected by measuring serum antibody titer against BLV virus antigen (gp51). The anti-BLV antibody titers of the BLV-infected cows were significantly higher in serum than in milk; a single serum-positive animal lacked detectable anti-BLV antibodies in its milk. Iron and ferritin concentrations also were significantly higher in serum than in milk. Although most of the BLV-infected dairy cows had past or present anamneses (such as inflammatory diseases, including intramammary infection), the milk ferritin concentrations of the infected cows were significantly lower than those of normal cows; serum ferritin concentrations did not differ significantly between these two groups. The anti-BLV antibody titers in milk samples showed significant correlation with serum iron concentrations. These results suggest that BLV infection affects iron homeostasis through iron metabolism in the dairy cow mammary gland.

Effects of bovine leukemia virus infection on milk neutrophil function and the milk lymphocyte profile

The effects of bovine leukemia virus (BLV) on the immune response have been extensively investigated; however, its effects on mammary gland immunity are only speculative. Although BLV has a tropism for B cells, it can affect both adaptive and innate immunities because these systems share many effector mechanisms. This scenario is the basis of this investigation of the effects of BLV on mammary gland immunity, which is largely dependent upon neutrophilic functions. Thus, the present study sought to examine neutrophilic functions and the lymphocyte profile in the milk of naturally BLV-infected cows. The viability of the milk neutrophils and the percentage of milk neutrophils that produced reactive oxygen species (ROS) or phagocytosed Staphylococcus aureus were similar between BLV-infected and BLV-uninfected dairy cows. Furthermore, the expression of CD62L and CD11b by the milk neutrophils and the percentage of milk neutrophils (CH138⁺ cells) that were obtained from the udder quarters of the BLV-infected cows were not altered. Conversely, the median fluorescence intensity (MFI) representing intracellular ROS production and the phagocytosis of S. aureus, the expression of CD44 by the milk neutrophils and the percentage of apoptotic B cells were lower in the milk cells from BLV-infected dairy cows, particularly those from animals with persistent lymphocytosis (PL). The lymphocyte subsets were not different among the groups, with the exception of the percentage of CD5⁻/CD11b⁻ B cells, which was higher in the milk cells from BLV-infected cows, particularly those with PL. Thus, the present study provides novel insight into the implications of BLV infection for mammary gland immunity.

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.

Vaccination against δ-retroviruses: the bovine leukemia virus paradigm

Bovine leukemia virus (BLV) and human T-lymphotropic virus type 1 (HTLV-1) are closely related δ-retroviruses that induce hematological diseases. HTLV-1 infects about 15 million people worldwide, mainly in subtropical areas. HTLV-1 induces a wide spectrum of diseases (e.g., HTLV-associated myelopathy/tropical spastic paraparesis) and leukemia/lymphoma (adult T-cell leukemia). Bovine leukemia virus is a major pathogen of cattle, causing important economic losses due to a reduction in production, export limitations and lymphoma-associated death. In the absence of satisfactory treatment for these diseases and besides the prevention of transmission, the best option to reduce the prevalence of δ-retroviruses is vaccination. Here, we provide an overview of the different vaccination strategies in the BLV model and outline key parameters required for vaccine efficacy.

Animal models of bovine leukemia virus and human T-lymphotrophic virus type-1: insights in transmission and pathogenesis

Bovine leukemia virus (BLV) and human T-lymphotrophic virus type-1 (HTLV-1) are related retroviruses associated with persistent and lifelong infections and a low incidence of lymphomas within their hosts. Both viruses can be spread through contact with bodily fluids containing infected cells, most often from mother to offspring through breast milk. Each of these complex retroviruses contains typical gag, pol, and env genes but also unique, nonstructural proteins encoded from the pX region. These nonstructural genes encode the Tax and Rex regulatory proteins, as well as novel proteins essential for viral spread in vivo. Improvements in the molecular tools to test these viral determinants in cellular and animal models have provided new insights into the pathogenesis of each virus. Comparisons of BLV and HTLV-1 provide insights into mechanisms of spread and tumor formation, as well as potential approaches to therapeutic intervention against the infections.

Lymphocytes and macrophages are infected by Theileria equi, but T cells and B cells are not required to establish infection in vivo

Theileria equi has a biphasic life cycle in horses, with a period of intraleukocyte development followed by patent erythrocytic parasitemia that causes acute and sometimes fatal hemolytic disease. Unlike Theileria spp. that infect cattle (Theileria parva and Theileria annulata), the intraleukocyte stage (schizont) of Theileria equi does not cause uncontrolled host cell proliferation or other significant pathology. Nevertheless, schizont-infected leukocytes are of interest because of their potential to alter host cell function and because immune responses directed against this stage could halt infection and prevent disease. Based on cellular morphology, Theileria equi has been reported to infect lymphocytes in vivo and in vitro, but the specific phenotype of schizont-infected cells has yet to be defined. To resolve this knowledge gap in Theileria equi pathogenesis, peripheral blood mononuclear cells were infected in vitro and the phenotype of infected cells determined using flow cytometry and immunofluorescence microscopy. These experiments demonstrated that the host cell range of Theileria equi was broader than initially reported and included B lymphocytes, T lymphocytes and monocyte/macrophages. To determine if B and T lymphocytes were required to establish infection in vivo, horses affected with severe combined immunodeficiency (SCID), which lack functional B and T lymphocytes, were inoculated with Theileria equi sporozoites. SCID horses developed patent erythrocytic parasitemia, indicating that B and T lymphocytes are not necessary to complete the Theileria equi life cycle in vivo. These findings suggest that the factors mediating Theileria equi leukocyte invasion and intracytoplasmic differentiation are common to several leukocyte subsets and are less restricted than for Theileria annulata and Theileria parva. These data will greatly facilitate future investigation into the relationships between Theileria equi leukocyte tropism and pathogenesis, breed susceptibility, and strain virulence.

Proliferação de linfócitos e apoptose de células CD5+ de bovinos infectados pelo vírus da leucose enzoótica bovina

Avaliaram-se a proliferação de linfócitos e a apoptose de células CD5+ de bovinos naturalmente infectados pelo vírus da leucose enzoótica bovina. Para tal, 100 vacas da raça Holandesa, em lactação, foram triadas quanto ao sorodiagnóstico para a leucose enzoótica bovina e o perfil hematológico, e 15 foram escolhidos e distribuídos uniformemente entre os três grupos, a saber: animais negativos, animais positivos alinfocitóticos e animais positivos e que manifestaram linfocitose persistente (LP). Para a avaliação da proliferação de linfócitos, procedeu-se ao isolamento das células mononucleares por gradiente de centrifugação, em que 2x10(6) linfócitos por mL foram plaqueados por poço e analisados por citometria de fluxo utilizando-se o fluorocromo CFSE-DA. A apoptose do sangue periférico deu-se utilizando a anexina V-FITC, e para a identificação das células CD5+, utilizaram-se anticorpos monoclonais. Ocorreu menor proliferação de linfócitos nos animais infectados e que manifestavam LP, e menor apoptose de células CD5+ do sangue periférico. Pode-se sugerir que o desenvolvimento da LP, resultante do aumento de linfócitos B, deve-se à redução do processo apoptótico das células CD5+, principal população infectada, e que a maior proliferação linfocitária pode se restringir apenas ao estádio inicial do desenvolvimento da LP.

Analysis of Syk expression in bovine lymphoma and persistent lymphocytosis induced by bovine leukemia virus

Spleen tyrosine kinase (Syk) is closely related to various cell reactions. In B-cells, Syk is involved in early B-cell receptor signaling, which affects cellular survival, proliferation and differentiation. Although the kinetics of Syk mRNA and its activity are variable in different types of tumor cells, Syk may have a relation to tumor progression in many human tumors, including B-cell lymphoma/leukemia. In this study we examined whether Syk mRNA expression was changed in bovine leukemia virus (BLV)-induced persistent lymphocytosis (PL) and lymphoma. As a result, we demonstrated that the Syk mRNA expression was significantly increased in PL samples, whereas it was decreased in tumor samples. Moreover one cow, which Syk mRNA expression has been lowest among PL cattle, developed lymphoma three months later and the expression significantly decreased. These data suggest that Syk mRNA expression dynamics is closely related to BLV-induced disease.

CD5 does not regulate the signaling triggered through BCR in B cells from a subset of B-CLL patients

CD5 is a transmembrane protein expressed on all T lineage cells and a subset of B cells. It is known that CD5 is physically associated with the T-cell receptor and B-cell receptor (BCR), inhibiting the signaling triggered by both of them. CD5 is also characteristic of B-chronic lymphocytic leukemia (B-CLL) B cells, although its implication in the development of this lymphoproliferative disorder has not been studied. In the present study, we examined the effect of CD5 in apoptosis, cell viability and global protein tyrosine phosphorylation mediated by BCR in B cells from B-CLL patients. As opposed to tonsil B cells, we did not observe an increase in the apoptotic or viability signals induced by anti-immunoglobulin M or SAC/interleukin-2 when CD5 was dissociated from BCR in leukemic cells of the majority of patients. We also observed that CD5 did not regulate the BCR-induced phosphotyrosine pattern in B-CLL B cells. These findings suggest that CD5 does not inhibit properly the BCR-mediated signaling in leukemic cells. This defect in inhibiting the BCR might contribute to the enhanced survival of B-CLL B cells.

The bovine antibody repertoire

Cattle are able to produce a full range of Ig classes including the long-elusive IgD through rearrangement of their germline genes. Several IgL groupings have been reported but as in several other livestock species (e.g. sheep, rabbits, chickens), rearrangement per se fails to generate significant IgH diversity. This is largely because of the modest number of bovine VH segments that participate in rearrangement and their conserved sequences. Perhaps in compensation, bovine Ig heavy chains carry CDR3 sequences of exceptional length. Processes that operate post-rearrangement to generate diversity remain ill defined as are the location, timing and triggers to these events. Reagents are needed to understand better the maturation of B lymphocytes, their responses to antigens and cytokines, and to provide standards for the quantitation of Ig responses in cattle; recombinant methods may help meet this need as Ab engineering technologies become more widely used.

Ex vivo survival of peripheral blood mononuclear cells in sheep induced by bovine leukemia virus (BLV) mainly occurs in CD5- B cells that express BLV

Bovine leukemia virus (BLV) is the etiologic agent of enzootic bovine leukosis (EBL). In a previous report, we found that in a sheep model, only CD5(-) B cells proliferated clonally, while CD5(+) B cells rapidly decreased when the disease progressed to the lymphoma stage. We demonstrate here that, although both CD5(+) and CD5(-) B cells, but not CD4(+) T, CD8(+) T and gammadeltaTCR(+)T cells, are protected from spontaneous ex vivo apoptosis in sheep infected with wild-type and a mutant BLV that encodes a mutant Tax D247G protein with elevated trans-activation activity, only CD5(-) B cells become the main target for ex vivo survival when the disease proceeds to the persistent lymphocytotic stage, which showed an increased expansion of the CD5(-) B cells. In addition, we identified, by four-color flow cytometric analysis, that in CD5(-) B cells, the apoptotic rates of cells that expressed wild-type and mutant BLV were greatly decreased compared with those of BLV-negative cells. There was only a slight reduction in the apoptotic rates in BLV-positive cells from CD5(+) B cells. In addition, supernatants from peripheral blood mononuclear cell (PBMC) cultures from wild-type- and mutant BLV-infected sheep mainly protected CD5(-) B cells from spontaneous apoptosis. Our results suggest that, although BLV can protect both CD5(+) and CD5(-) B cells from ex vivo apoptosis, the mechanisms accounting for the ex vivo survival between these two B-cell subsets differ. Therefore, it appears that the phenotypic changes in cells that express CD5 at the lymphoma stage could result from a difference in susceptibility to apoptosis in CD5(+) and CD5(-) B cells in BLV-infected sheep.

Reduced proviral loads during primo-infection of sheep by Bovine Leukemia virus attenuated mutants

Background

The early stages consecutive to infection of sheep (e.g. primo-infection) by Bovine leukemia virus mutants are largely unknown. In order to better understand the mechanisms associated with this period, we aimed at analyzing simultaneously three parameters: B-lymphocytosis, cell proliferation and viral replication.

Results

Sheep were experimentally infected either with a wild type BLV provirus or with selected mutants among which: a virus harboring an optimalized LTR promoter with consensus cyclic AMP-responsive elements, two deletants of the R3 or the G4 accessory genes and a fusion-deficient transmembrane recombinant. Seroconversion, as revealed by the onset of an anti-viral antibody response, was detected at 3 to 11 weeks after inoculation. At seroconversion, all sheep exhibited a marked increase in the numbers of circulating B lymphocytes expressing the CD5 and CD11b cluster of differentiation markers and, interestingly, this phenomenon occurred independently of the type of virus. The net increase of the absolute number of B cells was at least partially due to accelerated proliferation as revealed, after intravenous injection of bromodeoxyuridine, by the higher proportion of circulating BrdU+ B lymphocytes. BLV proviral DNA was detected by polymerase chain reaction in the leucocytes of all sheep, as expected. However, at seroconversion, the proviral loads were lower in sheep infected by the attenuated proviruses despite similar levels of B cell lymphocytosis.

Conclusions

We conclude that the proviral loads are not directly linked to the extent of B cell proliferation observed during primo-infection of BLV-infected sheep. We propose a model of opportunistic replication of the virus supported by a general activation process of B lymphocytes.

Engagement of the B-cell antigen receptor (BCR) allows efficient transduction of ZAP-70-positive primary B-CLL cells by recombinant adeno-associated virus (rAAV) vectors

Engagement of the B-cell antigen receptor (BCR) by crosslinking of the surface immunoglobulin (sIg) homodimer was studied for recombinant adeno-associated virus (rAAV)-mediated gene transfer into B-cell chronic lymphocytic leukaemia (B-CLL) cells. Leukemic cells obtained from 20 patients were stimulated with anti-sIg-directed antibodies and transduced with rAAV vectors coding for enhanced green fluorescent protein (EGFP) (AAV/EGFP) or CD40L (AAV/CD40L). Transduction of B-CLL cells was enhanced after BCR engagement compared to unstimulated controls (P=0.0356). BCR crosslinking induced a significant, dose- and time-dependent upregulation of heparan sulfate proteoglycan (HSPG), the primary receptor for AAV, on B-CLL cells (mean: 38.2 versus 1.7%; P=0.0006). A correlation of HSPG expression after BCR crosslinking with transduction efficiency by AAV/EGFP (P=0.0153) and AAV/CD40L (P=0.0347) was observed. High expression of zeta-associated protein 70 (ZAP-70) in B-CLL cells correlated with a better transduction efficiency by AAV/EGFP (P<0.0001) and AAV/CD40L (P=0.002), respectively: 48 h after transduction of ZAP-70-positive samples, transgene expression was seen in a mean of 33.8% (s.e.m. 3.7%) and 28.9% (s.e.m. 6.7%) of cells, respectively, and could be specifically blocked by heparin, a soluble competitor of HSPG (P<0.0001). In summary, engagement of the BCR on ZAP-70 positive B-CLL cells allows efficient rAAV-mediated gene delivery.

Translocation of the B cell receptor to lipid rafts is inhibited in B cells from BLV-infected, persistent lymphocytosis cattle

Bovine leukemia virus (BLV) infection causes a significant polyclonal expansion of CD5(+), IgM+ B lymphocytes known as persistent lymphocytosis (PL) in approximately 30% of infected cattle. There is evidence that this expanded B cell population has altered signaling, and resistance to apoptosis has been proposed as one mechanism of B cell expansion. In human and murine B cells, antigen binding initiates movement of the B cell receptor (BCR) into membrane microdomains enriched in sphingolipids and cholesterol, termed lipid rafts. Lipid rafts include members of the Src-family kinases and exclude certain phosphatases. Inclusion of the BCR into lipid rafts plays an important role in regulation of early signaling events and subsequent antigen internalization. Viral proteins may also influence signaling events in lipid rafts. Here we demonstrate that the largely CD5(+) B cell population in PL cattle has different mobilization and internalization of the BCR when compared to the largely CD5-negative B cells in BLV-negative cattle. Unlike B cells from BLV-negative cattle, the BCR in B cells of BLV-infected, PL cattle resists movement into lipid rafts upon stimulation and is only weakly internalized. Expression of viral proteins as determined by detection of the BLV transmembrane (TM) envelope glycoprotein gp30 did not alter these events in cells from PL cattle. This exclusion of the BCR from lipid rafts may, in part, explain signaling differences seen between B cells of BLV-infected, PL, and BLV-negative cattle and the resistance to apoptosis speculated to contribute to persistent lymphocytosis.

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.

Apoptosis induction by hypercross-linking of the surface antigen CD5 with anti-CD5 monoclonal antibodies in B cell chronic lymphocytic leukemia

We evaluated cells from 24 patients with B cell chronic lymphocytic leukemia (B-CLL) to determine apoptosis induced by CD5 hypercross-linking. Following the CD5 hypercross-linking with anti-CD5 monoclonal antibodies (MoAbs), we identified 10 patients where CD5 hypercross-linking induced apoptosis (group A) and 14 patients whose cells were resistant to the anti-CD5 MoAbs (group B). The programmed cell death pathway of the cells from patient group A was caspase-3 and poly (ADP-ribose) polymerase (PARP)-dependent, involved a reduction of the mitochondrial transmembrane potential DeltaPsi and a down-regulation of the anti-apoptotic Bcl-2, Mcl-1 and iNOS proteins. Early activation-associated molecules such as CD25 and CD69 were expressed at higher levels than in controls after 6 h of culture with anti-CD5 MoAb. The expression of CD5 and of CD72, the ligand for CD5, were significantly lower in group A compared with group B. Anti-CD20 MoAb had similar activity with anti-CD5 MoAb and the combination of the two MoAbs seemed to be additive. In this study, it is suggested that the cells from some B-CLL patients can be induced into programmed cell death by CD5 hypercross-linking with anti-CD5 MoAbs.