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

Optimized in vitro isolation of different subpopulation of immune cells from peripheral blood and comparative techniques for generation of monocyte-derived macrophages in small ruminants

Peripheral blood from healthy sheep (n = 3) and goats (n = 3) were employed to establish an efficient method for simultaneous isolation of peripheral blood mononuclear cells (PBMCs) and neutrophils and to standardize protocols for monocyte purification and generation of monocyte-derived macrophages (MDMs). In both species, a significantly enriched population of PBMCs, with higher purity and number of cells determined by flow cytometry, was achieved when processing through a density gradient a mixture of buffy-coat and red blood cell layer (RBC) in comparison to the use of just the buffy-coat (p <  0.05). Neutrophils could be subsequently isolated from the layer, located underneath PBMCs fraction with significant higher purity rates, higher than 85 % determined by flow cytometry, than those obtained with protocols without density gradients (< 60 %) (p <  0.05). This technique would allow the isolation of both cell populations from the same sample of blood. A pure cell population of monocytes, CD14⁺ cells, was purified from PBMCs when using immunomagnetic columns, which allow for 17 % (nº monocytes/nº PBMCs) of yield and high percentages of expression of CD14⁺ (88 %), MHC-II⁺ (91.5 %) and CD11b⁺ (94 %) established by flow cytometry. On the other hand, the classical and non-expensive purification of monocytes from PBMCs based on the adherence capacity of the former, allowed significantly lower yield of monocytes (4.6 %), with percentages of surface markers expression that dropped to 35 %, 65 % and 55 %, respectively (p < 0.001), suggesting the isolation of a mixed population of cells. The addition of GM-CSF to the culture, at concentration from 25 to 125 ng/mL, enhanced proportionally the number of MDMs generated compared to the absence of supplementation or the use of autologous serum from 5% to 20 %. However, purification of monocytes through the adherence method achieved higher yields of MDMs than those isolated through immunomagnetic columns in both species (p <  0.001). Under the conditions of this study, the use of centrifugation in density gradients allow for the simultaneous purification of PBMCs and neutrophils, with high purity of both populations, from the same sample of blood. The isolation of monocytes could be subsequently achieved through two different methods, i.e. based on immunomagnetic columns or adherence. The preference between both methods would depend on the necessities of the experiment, the initial sample with high purity of monocytes or a final population of MDMs required.

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

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

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

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

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

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

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.

Identification and gene expression of the bovine C-type lectin Dectin-1

C-type lectin receptors (CTLR) are cell-surface signalling molecules that recognize a range of highly conserved pathogen molecules and instigate the appropriate immune response. Here, we report the cloning, sequencing, mapping and expression pattern of the bovine C-type lectin domain family 7, member A (CLEC7A; synonyms CLCSF12, Dectin-1). We identified two isoforms, similar to the human system, with a long and short neck. Overall, the organization of the two bovine CLEC7A genes is similar to that of humans and mice. The CLEC7A gene maps on Bos taurus chromosome 5 (BTA5). mRNA transcripts for CLEC7A were detected in bone-marrow cells, monocytes, macrophages and dendritic cells and NK cells, but not in CD4(+) T-cells or CD21(+) B-cells. The increased knowledge of the genomic organization of the bovine CTLR genes may promote our understanding of their evolution and help in the identification of bovine genes underlying disease-resistance traits.

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

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