Abstract
Streptococcus suis (S. suis) is a major pathogen in pigs and an emerging zoonotic agent which causes serious infections in humans. It is also an immunosuppressive pathogen that exerts detrimental effects on the thymus, spleen, lymph nodes, and macrophages, impairing their ability to perform their normal physiological functions. S. suis induces thymic atrophy, splenomegaly, and lymphadenectasis and triggers apoptosis in T cells and B cells, as well as pyroptosis in macrophages within immune organs. Subsequently, T cell subsets in peripheral blood become abnormal, and the expression of cytokines becomes dysregulated, which leads to host immunosuppression, suggesting a new virulence mechanism of S. suis.