Interleukin 1 Receptor Antagonist (IL-1ra) Production and Expression Dynamics in Mammary Glands After Lipopolysaccharide Infusion

Interleukin-1 receptor antagonist (IL-1ra) is an anti-inflammatory cytokine, whose balance with pro-inflammatory cytokines affects the susceptibility to and severity of udder mastitis. In this study, we aimed to investigate the IL-1ra dynamics in the mammary gland immune system. Lipopolysaccharide (LPS group) or saline (control group) were infused into mammary gland of goats. Milk samples were collected 0–72 h after intramammary infusion. The results indicated that LPS infusion increased the somatic cell count and serum amyloid A level in milk, compared to those in the control group. The IL-1ra concentration in milk decreased after LPS infusion and was significantly lower at 4 h in the LPS group compared to that in the control group. The number of IL-1ra-positive cells significantly increased from 8 to 12 h in the LPS group. Immunohistochemistry revealed IL-1ra-positive cells in the alveolar connective tissue. Notably, the number of phagocytic cells and IL-1ra mRNA expression did not change significantly after LPS infusion. Overall, these results suggest that IL-1ra mRNA is expressed and synthesized in leukocytes, but is not secreted into milk for at least 72 h after intramammary LPS infusion. Furthermore, these findings highlight the role of IL-1ra in controlling inflammation in the mammary glands. © 2025 The Author(s). Animal Science Journal published by John Wiley & Sons Australia, Ltd on behalf of Japanese Society of Animal Science.