Research advances in the immunomodulatory mechanisms of probiotics on non-specific and specific immunity

Probiotics can regulate the body's immune system through both non-specific and specific immunity, thereby regulating host health. In terms of non-specific immune regulation, probiotics can activate the intrinsic immune system, regulate the mucosal barrier function, and play an immune role by influencing the activity of intrinsic immune cells such as macrophages, dendritic cells and natural killer cells, as well as their differentiation and maturation; in terms of specific immune regulation, probiotics play a role in regulating the immunoglobulin level and the maturation of B cells. Probiotics can also regulate T-cell differentiation according to the condition of the body, thus regulating specific immunity. Many studies have focused on the role of probiotics in metabolism and nutrition, and the mechanisms involved in the immunomodulatory role of probiotics have only been partially described. This review summarises the role of common probiotics such as <em>Lactobacillus plantarum</em> and <em>Lactobacillus rhamnosus</em> in immunomodulation as well as their mechanisms, describing the currently known mechanisms of immunomodulation by probiotics in improving the host immune system. A deeper understanding of probiotics and their specific mechanisms of action will facilitate the use of probiotics for immunomodulation in clinical medicine, functional foods, and other areas. This will also contribute to the development and research of engineered probiotics, next-generation probiotics, and other new functional probiotics with immunomodulatory effects.