Overview of the immune system

The immune system is split into two branches. The first is the adaptive immune system. Cells in the adaptive immune system, known as lymphocytes, produce chemicals specific to a particular foreign particle (antigen) when they encounter it. There are two main types of cell in the adaptive immune system – B lymphocytes and T lymphocytes. B lymphocytes grow into plasma cells, which release chemicals into the bloodstream and body called antibodies. Antibodies spread through the blood stream and help stop antigens by various methods (although they do not destroy foreign particles by themselves). T lymphocytes need to get close to the foreign particles and can destroy them by releasing damaging chemicals at a short range. Another type of T lymphocyte, known as a T helper cell, stimulates B lymphocytes and macrophages. Cells in the adaptive immune system can also become memory cells, which remember what the antigen was and what chemicals should be produced in response to that antigen. These memory cells allow a much faster and more powerful immune response on subsequent encounters.

The second branch of the immune system is known as the innate immune system. Cells in the innate immune system do not change their attack methods upon encountering different antigens, and are not specific to any particular antigens. There are many different types of cells in the innate immune system, such as phagocytes (cells which ingest foreign particles), basophils, eosinophils (both of which release chemicals), certain types of lymphocyte (similar in action to T lymphocytes), and mast cells (which are actually descended from basophils). Although it is the mast cells which release the chemicals involved allergy, the other types of cell may cause symptoms to become even worse.

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