Differences in cellular function and viral protein expression between IgMhigh and IgMlow B-cells in bovine leukemia virus-infected cattle

Expression of bovine leukaemia virus (BLV) gp51 protein in blood and milk cells of cows with leukosis

Introduction

Bovine leukaemia virus (BLV) is the retroviral causative agent of enzootic bovine leukosis, the most common neoplastic disease of cattle and a serious problem worldwide. Its diagnosis is commonly by tests for antibodies recognising the p24 capsid protein and structural glycoprotein (gp) 51. With flow cytometry recently having come to veterinary immunology, applications for it may now include BLV. The study determined BLV gp51 expression in blood and milk lymphocytes of naturally infected cows by flow cytometry.

Material and Methods

Nineteen Polish Black and White Lowland breed cows aged 4–9 years and naturally infected with BLV and ten uninfected counterparts had blood and milk sampled and cultured. The immunological status of the animals was confirmed with ELISA and PCR. Dual-colour flow cytometry analysis was performed with specific monoclonal antibodies for lymphocyte cluster of differentiation (CD) markers and gp51 viral envelope protein and conjugates labelled with fluorescein isothiocyanate or phycoerythrin. Bovine leukaemia virus gp51 was confirmed in lymphocytes by immunofluorescence with anti-gp51 monoclonal antibodies.

Results

The gp51 antigen was detected in blood and milk lymphocytes of infected cows, but the percentage of cells expressing it in milk was much lower than in blood. A depleted number of CD4+ lymphocytes, an augmented number of CD8+ lymphocytes, a lower ratio of CD4+ to CD8+ and a proliferation of CD19+ immunoglobulin M+ cells were also found.

Conclusion

These proliferated cells were immature, gave no sign of a tendency to differentiation and were characterised by prolonged vitality.

Establishment and Expression of Cytokines in a Theileria annulata-Infected Bovine B Cell Line

This study aimed to establish a pure single-cell Theileria annulata-infected B cell line for the assessment of cytokine production in transformed and lipopolysaccharide (LPS)-stimulated cells. Several studies have aimed to identify cell surface markers in T. annulata-transformed cells; however, no information on cytokine production in these cells is available. To investigate the potential of the transformed cells to produce cytokines and their potential responses to antigen-stimulation, we purified mature B cells (CD21) from the whole blood of cattle experimentally infected with the T. annulata Kashi strain by magnetic separation. The purity and specificity of the established cell line was assessed by the identification of specific cell surface markers (CD21, IgM, and WC4) by flow cytometry analysis. The transcript levels of the cytokines IL1A, IL1B, IL2, IL4, IL6, IL8, IL10, IL16, LTA, TGFB1, TNFA, IFNA, and IFNB in transformed, buparvaquone (BW720c)-treated cells, and antigen-stimulated cells were analyzed by quantitative polymerase chain reaction (qPCR) using cDNA from these cells. A T. annulata-infected bovine B cell line was successfully established with a purity of ~98.8% (CD21). IL4 and IL12A were significantly (p < 0.01) upregulated in the transformed cells. In BW720c-treated transformed cells, IL12B, TGFB1, and IFNB were significantly (p < 0.01) upregulated. Notably, no significant (p > 0.05) upregulation of cytokines was observed in LPS-stimulated transformed cells. Moreover, IL1A, IL1B, IL8, and IL16 were significantly (p < 0.01) upregulated in LPS-stimulated B cells. Our data signify the potential use of this cell line for cytokine production, observance of immunoglobulins, and production of an attenuated vaccine against tropical theileriosis.

Intrauterine infection with bovine leukemia virus in pregnant dam with high viral load

Enzootic bovine leukemia is caused by the bovine leukemia virus (BLV). BLV is transmitted vertically or horizontally through the transfer of infected cells via direct contact, through milk, insect bites and contaminated iatrogenic procedures. However, we lacked direct evidence of intrauterine infection. The purpose of this study was to confirm intrauterine BLV infection in two pregnant dams with high viral load by cesarean delivery. BLV was detected in cord and placental blood, and the BLV in the newborns showed 100% nucleotide identity with the BLV-env sequence from the dams. Notably, a newborn was seropositive for BLV but had no colostral antibodies. In this study, we presented a direct evidence of intrauterine BLV transmission in pregnant dam with a high proviral load. These results could aid the development of BLV control measures targeting viral load.

Identification of an Atypical Enzootic Bovine Leukosis in Japan by Using a Novel Classification of Bovine Leukemia Based on Immunophenotypic Analysis

Bovine leukemia is classified into two types: enzootic bovine leukosis (EBL) and sporadic bovine leukosis (SBL). EBL is caused by infection with bovine leukemia virus (BLV), which induces persistent lymphocytosis and B-cell lymphoma in cattle after a long latent period. Although it has been demonstrated that BLV-associated lymphoma occurs predominantly in adult cattle of >3 to 5 years, suspicious cases of EBL onset in juvenile cattle were recently reported in Japan. To investigate the current status of bovine leukemia in Japan, we performed immunophenotypic analysis of samples from 50 cattle that were clinically diagnosed as having bovine leukemia. We classified the samples into five groups on the basis of the analysis and found two different types of EBL: classic EBL (cEBL), which has the familiar phenotype commonly known as EBL, and polyclonal EBL (pEBL), which exhibited neoplastic proliferation of polyclonal B cells. Moreover, there were several atypical EBL cases even in cEBL, including an early onset of EBL in juvenile cattle. A comparison of the cell marker expressions among cEBL, pEBL, and B-cell-type SBL (B-SBL) revealed characteristic patterns in B-cell leukemia, and these patterns could be clearly differentiated from those of healthy phenotypes, whereas it was difficult to discriminate between cEBL, pEBL, and B-SBL only by the expression patterns of cell markers. This study identified novel characteristics of bovine leukemia that should contribute to a better understanding of the mechanism underlying tumor development in BLV infection.

Immune exhaustion during chronic infections in cattle

Recently, dysfunction of antigen-specific T cells is well documented as T-cell exhaustion and has been defined by the loss of effector functions during chronic infections and cancer in human. The exhausted T cells are characterized phenotypically by the surface expression of immunoinhibitory receptors, such as programmed death 1 (PD-1), lymphocyte activation gene 3 (LAG-3), T-cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) and cytotoxic T-lymphocyte antigen 4 (CTLA-4). However, there is still a fundamental lack of knowledge about the immunoinhibitory receptors in the fields of veterinary medicine. In particular, very little is known about mechanism of T cell dysfunction in chronic infection in cattle. Recent our studies have revealed that immunoinhibitory molecules including PD-1/ programmed death-ligand 1 (PD-L1) play critical roles in immune exhaustion and disease progression in case of bovine leukemia virus (BLV) infection, Johne's disease and bovine anaplasmosis. This review includes some recent data from us.