The structure and function of the immune system is a network of biological processes designed to protect an organism from diseases. This system detects and differentiates pathogens from healthy tissue, allowing it to fight off infection. Immune systems come in many forms and are divided into two main subsystems: the innate and adaptive. The innate immune system produces a predetermined response, while the adaptive immune system uses the information it has accumulated over time to tailor the immune response to the particular stimulus. These systems both employ cells and molecules to fight foreign pathogens.
The immunological process is complicated, involving complex biochemical processes that recognize and prosecute pathogens. These processes must be sufficient to protect a host. The immune system has traditionally been divided into two major subsystems, the innate and the adaptive. The innate immune system is organized around T and B cells and is centered on antigen-specific receptors. These specialized cells allow the immune system to customize its response to a particular infection and maintain an active immunological memory.
The immune system consists of 2×1012 lymphocytes that circulate in the blood and exist in organ-specific spatial structures. These cells have antigen-presenting and effector functions and interact with a variety of other cells in the body. They also communicate with each other by secreting cytokines. These cells have the capacity to act on distant cells. The immune system also works through the lymphatic system, which is a network of specialized vessels that transport lymph throughout the body.