Abstract
The implications of bovine leukemia virus (BLV) on innate and adaptive immune responses have been widely investigated; however, the effects of BLV on mammary gland immunity require further investigation. The present study investigated the viability, phagocytic capacity, and intracellular production of reactive oxygen and nitrogen species (RONS) by macrophages in milk samples from dairy cows naturally infected with BLV with or without persistent lymphocytosis (PL). No effect of BLV infection in the overall number of macrophages per milliliter and in the percentage of viable macrophages among overall milk viable cells was found. Furthermore, BLV-infected dairy cows had a higher frequency of viable milk macrophages, while healthy animals had a tendency toward a higher percentage of apoptotic milk macrophages. The percentage of milk macrophages that phagocytosed Staphylococcus aureus in seronegative animals was higher than that in BLV-infected dairy cows. No effect of BLV infection on the intracellular RONS production and the intensity of phagocytosis by milk macrophages was observed. Thus, this study provides new insights into the implications of BLV infections in the bovine mammary gland.
Highlights
Bovine leukemia virus (BLV) belongs to the family Retroviridae of the oncogenic genus Deltaretrovirus, which has tropism for B cells [1,2,3,4], it could infect and persist in other cell types, such as macrophages [1, 2]
Most studies on BLV demonstrate its impact on the adaptive immune system, some studies show that BLV infection negatively affects the performance of monocytes [5, 13, 40]; to the best of our knowledge, no study has investigated the impact of BLV infection on the function of milk macrophages
BLV persists mainly in B cells, monocytes and macrophages could be infected by BLV and act as a reservoir for BLV [1, 41]
Summary
Bovine leukemia virus (BLV) belongs to the family Retroviridae of the oncogenic genus Deltaretrovirus, which has tropism for B cells [1,2,3,4], it could infect and persist in other cell types, such as macrophages [1, 2]. The impact of chronic viral diseases with low lethality, especially BLV, is important when correlated with comorbidities, such as mastitis This disease remains one of the main health problems in dairy herds, and it has a direct impact on milk quality and public health due to the transmission of pathogens and antimicrobial residues in milk [4]. Infection by BLV negatively impacts the culling rate of dairy cattle, and AL animals may show decreased productivity and profitability [18] These findings raised questions about the effects of BLV on mammary gland immunity, in which macrophages are the main population present in milk from health mammary glands [19,20,21,22,23,24], being the first defense cells to come into contact with the pathogen that causes mastitis. Considering the importance of macrophages to the mammary gland during an infectious process, the present study investigated the phagocytic capacity and intracellular production of reactive oxygen and nitrogen species (RONS) by milk macrophages and their viability in BLV naturally infected dairy cows with or without PL
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