Exosomes Derived from Bovine Mammary Epithelial Cells Treated with Transforming Growth Factor-β1 Inhibit the Proliferation of Bovine Macrophages.

Transforming growth factor (TGF)-β1 is a multifunctional cytokine that plays an important role in regulating immune cell proliferation. We speculate that high expression of may affect the immunity of dairy cows. In this study, untreated exosomes (un-exo) derived from an untreated bovine mammary epithelial cell line (MAC-T) and -treated exosomes (t-exo) derived from -treated MAC-T cells were isolated by ultracentrifugation and identified by electron microscopy and Western blotting. Then, un-exo and t-exo were used to treat a bovine macrophage cell line (BOSMAC), and the proliferative ability of BOSMAC cells was detected by an 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay and flow cytometry. The expression and phosphorylation levels of p38 were analyzed by q-PCR and Western blotting. The results showed that both exosome types exhibited the basic characteristics of exosomes. In BOSMAC cells treated with t-exo, significant inhibition of cell proliferation was observed, and the cell cycle progression was inhibited, while no difference was found between the un-exo and control groups. Only treatment with t-exo increased the expression and phosphorylation of p38, and the addition of the p38 inhibitor SB203580 abrogated the inhibition of BOSMAC cell proliferation by t-exo. Our results demonstrated that t-exo inhibited the proliferation of bovine macrophages by stimulating p38 and might interfere with immunity in dairy cattle. This finding may provide a new strategy for improving immunity and preventing breast-related diseases in dairy cows.