In order to clarify and understand the immune mechanism of sheep mammary gland,this paper introduces the main tissues and immune substances involved in the immune defense of mammary gland,including breast papilla,mammary epithelial cells,white blood cells,immunoglobulin,complement system and chemical antibacterial agents,and describes the cooperation and interaction between them.The nipple of the breast papilla provides the initial protection for the breast.Mammary epithelial cells synthesize antibacterial proteins and white blood cells produce various inflammatory mediators（cytokines or chemokines）,engulf bacteria and recognize antigenic structures.In the mammary gland,four immunoglobulins（IgG1,IgG2,IgM and IgA） play an important role in combating bacterial pathogens.The complement system is a collection of proteins that participate in the inflammatory process through a variety of ways.Chemical antibacterial agents such as lactoferrin,lysozyme and lactoperoxidase contribute to the defense of breast fluid.

sheep  /  mammary epithelial cell  /  white blood cell  /  immunoglobulin  /  complement system  /  chemical antibacterial agent