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Bovine leukemia virus (BLV) main host cells are B lymphocytes. Infected animals can be classified into high or low proviral load (HPL or LPL respectively), regarding the number of proviral copies infected lymphocytes they carry. After infection, there is an overexpression of several cytokines, particularly TNF-α, which has a delicate regulation mediated by receptors TNFRI and TNFRII; the first one involved with apoptosis, while the other stimulates cell proliferation. The study aimed to quantify TNF-α and its receptors mRNA expression, and in which extent in vitro proliferation was affected, in peripheral blood mononuclear cells (PBMC) from BLV-infected animals with different proviral loads, after the addition or not of synthetic TNF-α (rTNF-α) for 48 h. PBMC from BLV-infected animals showed spontaneous proliferation after 48 h in culture but did not show changes in proliferation rates after 48 h incubation in the presence of the rTNF-α. TNF-α mRNA expression after 48 h culture without exogenous stimulation was significantly lower, regardless of the proviral load of the donor, compared to non-infected animals. In the LPL animals, the expression of TNF-α mRNA was significantly lower with respect to the control group while the expression of TNFRI mRNA was significantly increased. The HPL animals showed a significant decrease in the expression of TNF-α and TNFRII mRNA respect to the control group. After 48 h incubation with rTNF-α, PBMC from infected animals had different responses: TNF-α and TNFRI mRNA expression was reduced in PBMC from the LPL group compared to the BLV negative group, but no differences were observed in PBMC from the HPL group. TNFRII mRNA expression showed no differences between HPL, LPL, and BLV negative groups, though HPL animals expressed 10.35 times more TNFRI mRNA than LPL. These results support the hypothesis that LPL animals, when faced with viral reactivation, present a pro-apoptotic and anti-proliferative state. However, complementary studies are needed to explain the influence of TNFRII on the development of the HLP profile. On the other hand, exogenous stimulation studies reinforce the hypothesis that BLV infection compromises the immune response of the animals.

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Bovine leukemia virus (BLV) is a retrovirus that affects primarily milky cows. Animals serologically positive to BLV show a Th1 cytokine profile with a predominance of interferon gamma (IFN-γ). IFN-γ has antiviral activity through mechanisms such as resistance to infection, inhibition of viral replication and apoptosis. The objective of this work was to determine the transcription levels of IFN-γ and its relationship with proviral load and persistent lymphocytosis in a population of Holstein cows of the province of Antioquia, Colombia. IFN-γ transcription levels were evaluated by qPCR in 140 Holstein cows. A one-way analysis of variance and a Student's t test were used to evaluate the differences between the means. The amount of IFN-γ mRNA found in BLV-positive cows was lower than in BLV-negative cows. Moreover, in the group of infected cows a lower level of IFN-γ mRNA expression was found in BLV and persistent lymphocytosis cows (BLV+PL) compared with BLV and aleukemia cows (BLV+AL). The level of IFN-γ mRNA expression was lower in cows with high proviral load (HPL) compared to cows with low proviral load (LPL). BLV infection is related to abnormal expression of IFN-γ mRNA, although IFN-γ has antiviral activity, its expression is affected by high proviral load. Keywords: cytokine; immune system; leukemia; bovine leukemia virus.

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Bovine leukemia virus (BLV) is an important cattle pathogen that causes major economic losses worldwide, especially in dairy farms. The use of animal models provides valuable insight into the pathogenesis of viral infections. Experimental infections of sheep have been conducted using blood from BLV-infected cattle, infectious BLV molecular clones or tumor-derived cells. The Fetal Lamb Kidney cell line, persistently infected with BLV (FLK-BLV), is one of the most commonly used long-term culture available for the permanent production of virus. FLK-BLV cells or the viral particles obtained from the cell-free culture supernatant could be used as a source of provirus or virus to experimentally infect sheep. In this report, we aimed to determine the minimum amount of FLK-BLV cells or cell-free supernatant containing BLV needed to produce infection in sheep. We also evaluated the amount of antibodies obtained from a naturally-infected cow required to neutralize this infection. We observed that both sheep experimentally inoculated with 5000 FLK-BLV cells became infected, as well as one of the sheep receiving 500 FLK-BLV cells. None of the animals inoculated with 50 FLK-BLV cells showed evidence of infection. The cell-free FLK-BLV supernatant proved to be infective in sheep up to a 1:1000 dilution. Specific BLV antibodies showed neutralizing activity as none of the sheep became infected. Conversely, the animals receiving a BLV-negative serum showed signs of BLV infection. These results contribute to the optimization of a sheep bioassay which could be useful to further characterize BLV infection.

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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.

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Bovine leukemia virus (BLV) is a widespread infection that can affect innate and adaptive immunity; however, little information exists on how BLV infection affects foot-and-mouth disease virus (FMDV) vaccination programs. Vaccination for FMDV is compulsory in many regions of the world, and vaccine efficacy is monitored by measuring total antibodies against this virus. In a previous study, we observed that BLV-infected heifers produced a lower amount of antibodies in response to FMDV at first vaccination. In this follow-up study, we show that BLV status does not interfere with the total level and avidity of anti-FMDV-specific antibodies induced after repetitive routine vaccination in adult cattle. This is relevant information for the proficiency of vaccine-based FMDV control programs in BLV-endemic regions.

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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.

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El objetivo de este estudio fue determinar la prevalencia de anticuerpos en una manada de búfalos de río en la Isla de Marajó en busca de virus: Virus de la Diarrea Viral Bovina, Bovino Herpesvirus tipo 1 del Virus y la leucosis bovina enzoótica. La técnica de neutralización se utilizó para detectar anticuerpos relacionados con el virus de la diarrea viral bovina y virus del herpes bovino tipo 1 y la prueba de inmunodifusión en gel de agar para la detección de anticuerpos contra el virus de la leucosis bovina enzoótica. La prevalencia de anticuerpos contra el virus del herpes bovino tipo 1 en los búfalos está muy cerca de la prevalencia observada en el ganado bovino. La prevalencia de anticuerpos viral bovina virus de la diarrea mostró muy por debajo de la media en comparación con la prevalencia de anticuerpos en el ganado bovino y búfalos, también creado en el Brasil. La prevalencia del virus de la leucosis bovina enzoótica mostró, sin embargo, cerca del rango observado en búfalos en Brasil y en todo el mundo, que divergen de la prevalencia observada en los anticuerpos de ganado muy bajo, probablemente mostrando una resistencia natural al virus de este tipo, este factor debe ser mejor dilucidado.(AU)

The aim of this study was to determine the antibodies prevalence of Bovine viral diarrhea virus, Bovine herpesvirus 1 and Bovine leukemia virus in a herd of river buffaloes from the Marajó Island. The serum neutralization technique was used for the detection of Bovine viral diarrhea virus and Bovine herpesvirus 1 antibodies. The agar gel immunodiffusion (AGID) was used for the detection of Bovine leukemia virus antibodies. The prevalence of antibody to the Bovine herpesvirus 1 in buffaloes is very similar to the observed in cattle. The Bovine viral diarrhea virus showed a below average prevalence whether compared to the antibodies prevalence in cattle and buffaloes created in other parts of Brazil. The Bovine leukemia virus showed a very low prevalence of antibodies, however, these parameters were similar to others observed in buffaloes in Brazil and worldwide. These parameters differ from the prevalence observed in cattle, which probably suggests a natural resistance from this specie to the virus. This fact, however, needs to be further elucidated.(AU)

O objetivo do presente estudo foi determinar a prevalência de anticorpos em um rebanho de búfalos de rio da Ilha de Marajó para os vírus: Vírus da diarreia viral bovina, Herpesvírus bovino tipo 1 e Vírus da leucose enzoótica bovina. A técnica de soroneutralização foi utilizada para detecção de anticorpos referentes aos Vírus da diarreia viral bovina e Herpesvírus bovino tipo 1 e o teste de imunodifusão em gel de ágar para detecção de anticorpos para o Vírus da leucose enzoótica bovina. A prevalência de anticorpos para o Herpesvírus bovino tipo 1 em bubalinos está muito próxima da prevalência observada em bovinos. O Vírus da diarreia viral bovina apresentou prevalência de anticorpos muito abaixo da média quando comparada com prevalência de anticorpos em bovinos e bubalinos, inclusive criados no Brasil. O Vírus da leucose enzoótica bovina mostrou prevalência de anticorpos muito baixa, porém, próxima dos parâmetros observados em búfalos no Brasil e no mundo, que divergem da prevalência observada em bovinos, mostrando provavelmente uma resistência natural dessa espécie ao vírus, fator esse que precisa ser mais bem elucidado.(AU)

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El objetivo de este estudio fue determinar la prevalencia de anticuerpos en una manada de búfalos de río en la Isla de Marajó en busca de virus: Virus de la Diarrea Viral Bovina, Bovino Herpesvirus tipo 1 del Virus y la leucosis bovina enzoótica. La técnica de neutralización se utilizó para detectar anticuerpos relacionados con el virus de la diarrea viral bovina y virus del herpes bovino tipo 1 y la prueba de inmunodifusión en gel de agar para la detección de anticuerpos contra el virus de la leucosis bovina enzoótica. La prevalencia de anticuerpos contra el virus del herpes bovino tipo 1 en los búfalos está muy cerca de la prevalencia observada en el ganado bovino. La prevalencia de anticuerpos viral bovina virus de la diarrea mostró muy por debajo de la media en comparación con la prevalencia de anticuerpos en el ganado bovino y búfalos, también creado en el Brasil. La prevalencia del virus de la leucosis bovina enzoótica mostró, sin embargo, cerca del rango observado en búfalos en Brasil y en todo el mundo, que divergen de la prevalencia observada en los anticuerpos de ganado muy bajo, probablemente mostrando una resistencia natural al virus de este tipo, este factor debe ser mejor dilucidado.

The aim of this study was to determine the antibodies prevalence of Bovine viral diarrhea virus, Bovine herpesvirus 1 and Bovine leukemia virus in a herd of river buffaloes from the Marajó Island. The serum neutralization technique was used for the detection of Bovine viral diarrhea virus and Bovine herpesvirus 1 antibodies. The agar gel immunodiffusion (AGID) was used for the detection of Bovine leukemia virus antibodies. The prevalence of antibody to the Bovine herpesvirus 1 in buffaloes is very similar to the observed in cattle. The Bovine viral diarrhea virus showed a below average prevalence whether compared to the antibodies prevalence in cattle and buffaloes created in other parts of Brazil. The Bovine leukemia virus showed a very low prevalence of antibodies, however, these parameters were similar to others observed in buffaloes in Brazil and worldwide. These parameters differ from the prevalence observed in cattle, which probably suggests a natural resistance from this specie to the virus. This fact, however, needs to be further elucidated.

O objetivo do presente estudo foi determinar a prevalência de anticorpos em um rebanho de búfalos de rio da Ilha de Marajó para os vírus: Vírus da diarreia viral bovina, Herpesvírus bovino tipo 1 e Vírus da leucose enzoótica bovina. A técnica de soroneutralização foi utilizada para detecção de anticorpos referentes aos Vírus da diarreia viral bovina e Herpesvírus bovino tipo 1 e o teste de imunodifusão em gel de ágar para detecção de anticorpos para o Vírus da leucose enzoótica bovina. A prevalência de anticorpos para o Herpesvírus bovino tipo 1 em bubalinos está muito próxima da prevalência observada em bovinos. O Vírus da diarreia viral bovina apresentou prevalência de anticorpos muito abaixo da média quando comparada com prevalência de anticorpos em bovinos e bubalinos, inclusive criados no Brasil. O Vírus da leucose enzoótica bovina mostrou prevalência de anticorpos muito baixa, porém, próxima dos parâmetros observados em búfalos no Brasil e no mundo, que divergem da prevalência observada em bovinos, mostrando provavelmente uma resistência natural dessa espécie ao vírus, fator esse que precisa ser mais bem elucidado.

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BACKGROUND: Bovine Leukemia Virus (BLV) produces disorders on the immune system in naturally infected animals, which may counteract the development of immunity after vaccination. The aim of this study was to investigate whether healthy and BLV infected cattle elicited similar humoral responses after foot and mouth disease (FMD) immunization. In a field study, 35 Holstein heifers were selected based on their BLV serological status and immunized with a single dose of a commercial bivalent oil-based FMD vaccine. Serum samples were collected at 0, 15, 60, 165 and 300 days post vaccination (dpv). RESULTS: Total anti-A24/Cruzeiro antibodies, IgM, IgG1, IgG2 titers and avidity index of specific antibodies were determined by ELISA. Although only marginally significant differences were found between groups in terms of total antibodies, anti-FMD IgM and IgG1 titers were significantly lower in heifers infected with BLV at the 15 dpv (p < 0.01). Animals that became infected during the study did not show differences to the BLV negative group. CONCLUSIONS: Cattle infected with BLV at the time of immunization may elicit a low-magnitude serological response to a commercial Foot-and-mouth disease vaccine.

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Background: Viral diseases affecting reproduction cause economic losses in cattle, as reproductive failure interrupts the production cycle, thus reducing herd productivity. Buffaloes are susceptible to most of the diseases that affect cattle. Some of the viral diseases of reproductive importance are infectious bovine rhinotracheitis (IBR), bovine viral diarrhea (BVD), and bovine leukosis (BL). The objective of this study was to determine the seroprevalence of IBR virus (bovine herpes virus-1, BoHV-1), BVD virus (BVDV), and BL virus (BLV) in female buffaloes living in wetland areas or plains in the state of Pará, as well as the seroprevalence of BoHV-1, BVDV, and BLV in females of different age groups. Materials, Methods & Results: It were used 225 crossbred buffaloes from 4 buffalo exclusive farms. The buffaloes reared on farms A (n = 50) and B (n = 89) were kept in wetland areas on Marajó Island (n = 139), Pará. On farms C (n = 30) and D (n = 56) buffaloes were kept in plains (n = 86) in a northeastern mesoregion of Para. Animals were categorized into age groups: I: 0-3 years (n = 34), II: 3-6 years (n = 58), III: 7-9 years (n = 55), and IV: over 9 years (n = 78). Blood samples were collected and sera were sent for processing at the Bovine Virus Laboratory, Biological Institute of São Paulo, Brazil. The presence of IBRV and BVDV was determined by neutralization and BLV [...](AU)

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Background: Viral diseases affecting reproduction cause economic losses in cattle, as reproductive failure interrupts the production cycle, thus reducing herd productivity. Buffaloes are susceptible to most of the diseases that affect cattle. Some of the viral diseases of reproductive importance are infectious bovine rhinotracheitis (IBR), bovine viral diarrhea (BVD), and bovine leukosis (BL). The objective of this study was to determine the seroprevalence of IBR virus (bovine herpes virus-1, BoHV-1), BVD virus (BVDV), and BL virus (BLV) in female buffaloes living in wetland areas or plains in the state of Pará, as well as the seroprevalence of BoHV-1, BVDV, and BLV in females of different age groups. Materials, Methods & Results: It were used 225 crossbred buffaloes from 4 buffalo exclusive farms. The buffaloes reared on farms A (n = 50) and B (n = 89) were kept in wetland areas on Marajó Island (n = 139), Pará. On farms C (n = 30) and D (n = 56) buffaloes were kept in plains (n = 86) in a northeastern mesoregion of Para. Animals were categorized into age groups: I: 0-3 years (n = 34), II: 3-6 years (n = 58), III: 7-9 years (n = 55), and IV: over 9 years (n = 78). Blood samples were collected and sera were sent for processing at the Bovine Virus Laboratory, Biological Institute of São Paulo, Brazil. The presence of IBRV and BVDV was determined by neutralization and BLV [...]

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Bovine Leukemia Virus (BLV) is endemic in Argentina, where the individual prevalence is higher than 80% in dairy farms. The aim of this work was to find preliminary evidence to know if the high level of infection of the dam would implicate a higher challenge to her own offspring. We collected 65 sets of samples consisting of dam's blood and colostrum from two heavily infected dairy farms, and investigated the correlation between the dam's blood proviral load and the presence of provirus in colostrum. We also described the dual antibody/provirus profile in the colostrum. Provirus was detected in 69.23% of the colostrum samples, mostly from dams with a high proviral load, 36/45 (80%). Colostrum proviral load was significantly higher in dams with high blood proviral load (p<0.0001). Provirus was detected in colostrum samples all along the antibody distribution, even in those with a low amount of antibodies. These results show that even when high blood proviral load dams offer higher levels of infected cells to their offspring through colostrum they also offer higher levels of protection of antibodies. On the contrary, low blood proviral load dams also offer infected cells but a poor content of antibodies, suggesting that these animals could play an important role in the epidemiological cycle of transmission.

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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.

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Background: Bovine leukemia virus (BLV) is a retrovirus. It is common infectious viruses of cattle with worldwide distribution. Milk from infected cows often contains BLV-infected cells are a common cause of infection. Eradication andcontrol of BLV is based on early diagnostic. Both serum and milk samples can be tested by ELISA and it is possible to testeither individual samples or, at a herd level, milk cooling tanks (MCT) samples. The aim of this study is to determine BLVantibodies (Abs) in the MCT, milk cans, and individual blood and milk samples of dairy cows in dairy cattle managementslocated in Burdur center and its districts and to follow and study the infection on the milk production chain.Materials, Methods & Results: Milk samples were collected from 50 main MCT. Studies were carried out in the managements that seven BLV Ab (+) and seven Ab (-) in their main MCT were located. For this purpose, milk samples werecollected from mixed milk cans that were collected from managements providing milk for main MCT. Blood and milksamples were collected from dairy cows, housed in managements where BLV Ab (+) and Ab (-) was detected. Highestand lowest percent BLV (+) management, percent BLV (+) can numbers and percent milk amount were in 1 ton and 2ton MCT, respectively. Moreover, these parameters were paralleled in all MCT. Percent BLV (+) and milk amounts werehighest in 3 ton MCT and lowest in 2 ton MCT. In addition, these parameters were paralleled in all MCT. Distributionsin BLV (+) managements ranged from 15 to 75%. It was detected at the individual animal levels, BLV (+) milk sampledistributions ranged between 7.4 and 38.4%. Age range of the BLV (+) cows was between 3 and 11 years. Individual BLVtests between milk and serum samples were correlated positively in 5 managements (71.4%). On the other hand, the correlation was not detected in 2 of the managements (28.6%) that the individual milk and serum samples were collected. BLV...

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Background: Bovine leukemia virus (BLV) is a retrovirus. It is common infectious viruses of cattle with worldwide distribution. Milk from infected cows often contains BLV-infected cells are a common cause of infection. Eradication andcontrol of BLV is based on early diagnostic. Both serum and milk samples can be tested by ELISA and it is possible to testeither individual samples or, at a herd level, milk cooling tanks (MCT) samples. The aim of this study is to determine BLVantibodies (Abs) in the MCT, milk cans, and individual blood and milk samples of dairy cows in dairy cattle managementslocated in Burdur center and its districts and to follow and study the infection on the milk production chain.Materials, Methods & Results: Milk samples were collected from 50 main MCT. Studies were carried out in the managements that seven BLV Ab (+) and seven Ab (-) in their main MCT were located. For this purpose, milk samples werecollected from mixed milk cans that were collected from managements providing milk for main MCT. Blood and milksamples were collected from dairy cows, housed in managements where BLV Ab (+) and Ab (-) was detected. Highestand lowest percent BLV (+) management, percent BLV (+) can numbers and percent milk amount were in 1 ton and 2ton MCT, respectively. Moreover, these parameters were paralleled in all MCT. Percent BLV (+) and milk amounts werehighest in 3 ton MCT and lowest in 2 ton MCT. In addition, these parameters were paralleled in all MCT. Distributionsin BLV (+) managements ranged from 15 to 75%. It was detected at the individual animal levels, BLV (+) milk sampledistributions ranged between 7.4 and 38.4%. Age range of the BLV (+) cows was between 3 and 11 years. Individual BLVtests between milk and serum samples were correlated positively in 5 managements (71.4%). On the other hand, the correlation was not detected in 2 of the managements (28.6%) that the individual milk and serum samples were collected. BLV...(AU)

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A peroxidase linked assay (PLA) was designed to screen bovine sera for the presence of specific antibodies against bovine leukosis virus (BLV). Out of 201 samples of bovine sera analyzed, 52.2% were considered positive by PLA, 26.4% by AGID, and 38.9% by ELISA. Western blotting analyses excluded 27 samples found to be positive by PLA. PLA showed 100% of sensitivity when compared with AGID and ELISA. Specificity was 64.8% and 78%, respectively (kappa coefficients were 0.70 and 0.83). These findings indicate that PLA can be used as an alternative method for the diagnosis of BLV infection in cattle.

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OBJECTIVE: To determine the reference interval for WBC counts in Holstein dairy cows from herds with high seroprevalence for anti-bovine leukemia virus (BLV) antibodies, analyze the correlation of total WBC counts and blood proviral load (bPVL) in BLV-infected animals, and determine whether total WBC count can be used a hematologic marker for in vivo infection. ANIMALS: 307 lactating cows from 16 dairy herds with high BLV seroprevalence. PROCEDURES: Blood samples were collected for assessment of plasma anti-BLV p24 antibody concentration (all cows), manual determination of WBC count (161 BLV-seronegative cows from 15 herds), and evaluation of bPVL (146 cows from another herd). RESULTS: The WBC count reference interval (ie, mean ± 2 SD) for BLV-seronegative dairy cows was 2,153 to 11,493 cells/µL. Of the 146 cows used to analyze the correlation between WBC count and bPVL, 107 (73%) had WBC counts within the reference interval; of those cows, only 21 (19.6%) had high bPVL. Most cows with high WBC counts (35/39) had high bPVL. Mean WBC count for cows with high bPVL was significantly higher than values for cows with low or undetectable bPVL. White blood cell counts and bPVL were significantly (ρ = 0.71) correlated. CONCLUSIONS AND CLINICAL RELEVANCE: These data have provided an updated reference interval for WBC counts in Holstein cows from herds with high BLV seroprevalence. In dairy cattle under natural conditions, WBC count was correlated with bPVL; thus, WBC count determination could be a potential tool for monitoring BLV infection levels in attempts to control transmission.

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BACKGROUND: Bovine leukemia virus (BLV) is worldwide distributed and highly endemic in Argentina. Among the strategies to prevent BLV dissemination, a control plan based on the selective segregation of animals according to their proviral load (PVL) is promising for our dairy productive system. The objective of this work was to study the relationship between the blood PVL and the antibody level, in order to identify whether the individual humoral response, i.e. the anti-p24 or anti-whole-BLV particle, could be used as a marker of the blood level of infection and thus help to recruit animals that may pose a lower risk of dissemination under natural conditions. RESULTS: The prevalence of p24 antibodies on the 15 farms studied was over 66%. The prevalence of p24 and whole-BLV antibodies and PVL quantification were analyzed in all the samples (n = 196) taken from herds T1 and 51. ROC analysis showed a higher AUC for p24 antibodies than whole-BLV antibodies (Z(reactivity): 3.55, P < 0.001; Z(titer): 2.88, P < 0.01), and as consequence a better performance to predict the proviral load status in herd 51. No significant differences were found between the performance of p24 and whole-BLV antibodies in herd T1. A significant positive correlation was observed between PVL values and p24 antibody reactivity in both farms (r (T1) = 0.7, P < 0.001, r (51) = 0.71, P < 0.0001). The analysis was extended to the whole number of weak p24 antibody reactors (n = 311) of the other 13 farms. The mean of high PVL reactors within weak p24 reactors was 17.38% (SD = 8.92). In 5/15 farms, the number of weak p24 reactors with high PVL was lower than 10%. CONCLUSIONS: We found that the humoral response reflected the level of in vivo infection, and may therefore have useful epidemiological applications. Whereas the quantitative evaluation of blood proviral load using real-time PCR is expensive and technically demanding, the measurement of antibodies in blood by ELISA is relatively straightforward and could therefore constitute a cost-effective tool in a BLV control intervention strategy, especially in highly infected herds such as Argentinean dairy ones.

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Dentre os vários fatores que podem influenciar a polarização das respostas imunológicas nos animais destacam-se o tipo do agente agressor envolvido, as células apresentadoras de antígenos atuantes no processo e o microambiente formado pelas citocinas. Diferentes perfis de citocinas podem determinar o curso da doença, uma vez que distúrbios no equilíbrio da produção e liberação destes polipeptídeos têm papel significativo no desencadeamento e agravamento de diversas enfermidades. Vírus podem interferir com as funções das citocinas em vários níveis, influenciando na natureza da resposta imune do hospedeiro. Este desequilíbrio entre a produção de citocinas do tipo Th1 e Th2 é geralmente considerado como uma das causas da cronificação das infecções por retrovírus. O VLB, assim como outros retrovírus, também possui esta capacidade de manipular a resposta imune do hospedeiro a fim de direcionar os estágios alinfocitóticos (AL) e de linfocitose persistente (LP). No entanto, seu efeito diretamente sobre as citocinas no sangue e leite dos animais infectados ainda não foi completamente elucidado. Desta forma, o presente estudo objetivou a avaliação da resposta imune contra o VLB em vacas naturalmente infectadas por meio da quantificação de um perfil abrangente de citocinas presentes tanto no soro sanguíneo como no lácteo minimizados outros aspectos de estimulação que não fossem a presença do próprio vírus in vivo. [...] Os resultados obtidos apontam para um envolvimento do VLB sobre o perfil de citocinas da glândula mamária nos animais sororreagentes

Among the many factors that can influence the polarization of immune responses in animals include the type of the offending agent involved, the antigen-presenting cells active in the process and the microenvironment formed by the cytokine. Different profiles of cytokines may determine the course of the disease, since disturbances in the balance of production and release of these polypeptides play a significant role in triggering and worsening of many diseases. Viruses can interfere with the functions of cytokines at various levels, influencing the nature of the host immune response. This imbalance in cytokine production from Th1 and Th2 is generally regarded as a cause of chronic infections by retroviruses. The BLV, like other retroviruses, also possess this ability to manipulate the host immune response in order to drive the stages non-lymphocytotic and persistent lymphocytosis. However, its effect directly on cytokines in blood and milk of infected animals has not been fully elucidated. Thus, this study aimed at evaluating the immune response against the BLV in cows naturally infected by quantifying a comprehensive profile of cytokines present in both the serum and in whey minimized others aspects of stimulation that was not the presence of the virus itself in vivo. [...] The results indicate an involvement of BLV on the cytokine profile of the mammary gland in animals seropositive

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RESUMO

The present study assesses the oxidative burst activity from polymorphonuclear leukocytes (PMNLs) from bovine leukemia virus (BLV)-infected cows. Fifteen clinically healthy cows were divided into serologically positive cows without any hematological alteration, serologically positive animals with persistent lymphocytosis (PL) and healthy serologically negative cows. The oxidative burst activity from the PMNLs was evaluated by flow cytometry using 2',7'-dichlorofluorescein diacetate as a probe. PMNLs from each cow were incubated with heat-killed Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) to stimulate oxidative burst activity. The results of the present work showed no significant difference in the oxidative burst activity without any stimulus and elicited by S. aureus. Conversely, a decrease in the oxidative burst index induced by E. coli in PMNLs was observed in BLV-infected cows.

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