Abstract
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.
Highlights
Bovine leukemia virus (BLV) is a member of the Retroviridae family and the Deltaretrovirus genus that is genetically and structurally similar to the primate T-lymphotropic viruses types 1–5 (i.e., HTLV-1 to 4)
These findings prompted an investigation into the effects of BLV, which is a B cell tropic virus [1,6,15], on mammary gland immunity, which is largely dependent upon neutrophil functions and recruitment
These animals were divided uniformly into the following three groups according to the sera test results: negative for BLV infection according to the agar gel immunodiffusion (AGID) and ELISA assays and lacking hematological alterations [43]; positive for BLV according to both tests and lacking hematological alterations [43], which is commonly referred to as aleukemic (AL; n = 6; quarters); and positive for BLV according to both tests and exhibiting persistent lymphocytosis (PL) (n = 5; quarters)
Summary
Bovine leukemia virus (BLV) is a member of the Retroviridae family and the Deltaretrovirus genus that is genetically and structurally similar to the primate T-lymphotropic viruses types 1–5 (i.e., HTLV-1 to 4). Mastitis [23,24,25,26,27,28,29,30] and decreased milk production [31,32,33,34,35] have been associated with BLV infection, in BLV-infected cows with PL [31] and high-performing infected dairy herds [35] These findings prompted an investigation into the effects of BLV, which is a B cell tropic virus [1,6,15], on mammary gland immunity, which is largely dependent upon neutrophil functions and recruitment. The impact of some chronic diseases with low lethality, such
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