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;
