Immune System Development

1. Immune System Development The immune system has the function of immune surveillance, defense, and regulation. This system consists of immune organs (bone marrow, spleen, lymph nodes, tonsils, small intestine collecting lymph nodes, appendix, thymus, etc.), immune cells (lymphocytes, mononuclear phagocytic cells, neutrophils, basophils, eosinophils, Mast cells, platelets (because of IgG in platelets), and immunologically active substances (antibody, lysozyme, complement, immunoglobulin, interferon, interleukin, tumor necrosis factor and other cytokines). The immune system is divided into innate immunity (also known as non-specific immunity) and adaptive immunity (also known as specific immunity), wherein adaptive immunity is divided into humoral immunity and cellular immunity. The development of the immune system is essential for the normal growth of the body. If the immune system is not properly developed, it will induce related diseases. The basic function of the immune system is to identify self and non-self while generating different response strategies. According to current understanding, the evolution of the immune system can be roughly divided into five levels. The first level is characterized by the specific aggregation of the same species to compete for survival, and found in plants, cavernous, protozoa, etc.; the second level is characterized by specific differentiated immune cell-mediated non-memory immune recognition and immunity reactions, such as coelenterates;