Over a long period of time, animals have built defense mechanisms to block external intruders through a complex evolutionary process. The structure created at the center is called the immune system. In animals with a vascular system, immune cells circulating in the blood perform most of the role. Cytokines are substances that direct immune function and are not only produced by immune cells but also secreted by non-immune cells, contributing to the proliferation and differentiation of blood cells. Most blood cells are red blood cells that supply oxygen in the body, and a small number of white blood cells (WBC) perform immune functions. Even under normal circumstances, mammalian WBC are produced in the bone marrow, differentiate into various immune cells, and proliferate under the stimulation of cytokines. However, when infected with external pathogens, viruses, bacteria, fungi, and parasites, cytokines are produced exponentially and temporarily induce proliferation and differentiation of immune cells defending the host from pathogens. Once all pathogens are destroyed by immune cells, excessive cytokine activity is downregulated by soluble antagonists, such as cytokine binding proteins and ligands, but which have receptor antagonist properties. In this review, we will discuss the roles of cytokines, which are immune enhancers, and soluble cytokine binding proteins, which are immunosuppressants, and various autoimmune diseases that arf44ise from immune imbalance.