Immunosuppression and Immune Escape

The immune system is an important defense system of the organism that has evolved over time. Innate immunity is an immune response in animals through recognition of pathogens by pattern recognition receptors (PRRs), which rapidly suppress and clear pathogens early during pathogenic infection. In addition to innate immunity, the immune system of higher animals has evolved adaptive immunity, which is the production of humoral and/or cellular immune responses to pathogens, more efficient clearance of pathogenic infections, and the generation of immune memory, as well as the elimination of mutated cells in the body to maintain homeostasis. However, certain pathogens, after infecting the host, suppress the immune response and reduce host immunity, resulting in persistent, secondary and mixed infections. If the animal is immunocompromised, tumor cells evade immune surveillance, resulting in neoplastic disease. This chapter does not involve immunodeficiency due to genetic causes, mainly focusing on the mechanisms underlying pathogen-induced immunosuppression and immune escape of tumor cell from host immunity.