Abstract
A previous study found that repeated intrauterine infusions of lipopolysaccharide (LPS) followed by an LPS infusion into the mammary glands attenuated the mammary inflammatory response. This suggests that repeated LPS infusion into the uterus promotes endotoxin tolerance (ET) in the mammary gland. However, the specific changes in mammary glands under ET conditions remain unclear. We hypothesized that ET affects leukocyte function in milk. This study aimed to investigate leukocyte function in milk under ET conditions induced through repeated LPS infusions into the uterus for three days followed by LPS infusion into the mammary glands of goats. Goats in the IU group (n = 17) received an infusion of 100 μg LPS in 5 ml saline into the uterus for three consecutive days (d -3, -2, and -1), whereas the goats in the control group did not receive this infusion (n = 19). On d 0, 1 μg LPS in 5 ml saline was infused into the mammary glands of both groups. Milk was collected 0, 4, 8, 12, 24, 48, 72, and 120 h after LPS intramammary infusion. The IU group decreased cytokine production (interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and IL-1Ra) in milk following intramammary LPS infusion. Moreover, leukocyte activation, measured by phagocytic activity and CD11b expression, was higher in the IU group than in the control group. These findings suggest that goats exhibit enhanced leukocyte function in mammary glands under ET conditions, induced by repeated intrauterine infusion of LPS.