What we know of [the immune system] is staggering. It begins at the skin, a barrier capable of synthesising biochemicals that inhibit the growth of certain bacteria and containing, in its deepest layers, cells that can induce inflammation and ingest pathogens. Then there are the membranes of the digestive, respiratory and urogenital systems with their pathogen-ensnaring mucous ad they pathogen-expelling cilia and their high concentrations of cells equipped to produce the antibodies responsible for lasting immunity. Beyond those barriers, the circulatory system transports pathogens in the blood to the spleen, where the blood is filtered and antibodies are generated, and the lymphatic systems flushes pathogens from body tissues to the lymph nodes, where the same process ensues…
Deep in the body, the bone marrow and the thymus generate a dizzying arrange of cells specialised for immunity. These include cells that can destroy infected cells, cells that swallow pathogens and then display pieces of them for other cells to see, cells that monitor other cells for signs of cancer or infection, cells that make antibodies, and cells that carry antibodies. All of these cells, falling into an intricate arrangement of types and subtypes, interact in a series of baroque dances, their communication depending in part on the action of free-floating molecules. Chemical signals travel through the blood from sites of injury or infection, activated cells release substances to trigger inflammation, and helpful molecules poke holes in the membranes of microbes that deflate them.from On Immunity by Eula Biss (2014)
Image: model of Immunoglobulin G from here.
