The adaptive immune system is made up of three main components – T cells, B cells, and antibodies.
T cells
T cells are also known as T lymphocytes. They originate in the bone marrow. Immature T cells move through the bloodstream to the thymus where they undergo maturation. In the thymus, T cells also undergo specialization, differentiating into three types of T cells, each of which performs a specialized role within the adaptive immune system.
- Helper T cellsare responsible for activating the adaptive immune system by messaging other immune system cells using signaling molecules. After the pathogens are destroyed and the infection is eliminated, some helper T cells become memory cells, which are capable of memorizing which pathogens were defeated. They use this immunologic memory to activate the adaptive immune system even faster in case of a subsequent infection.
- Cytotoxic T cells are responsible for detecting and destroying tumorous cells or cells infected by viruses.
B cells
B cells, also known as B lymphocytes, originate and mature in the bone marrow. They also become specialized immune system cells in the bone marrow itself.
B cells are activated by the helper T cells. In the event of an infection, helper T cells message and activate specific B cells, which multiply and transform into plasma cells that are capable of producing copious amounts of antibodies very quickly. The newly produced antibodies are released into the blood and used to destroy the pathogen.
Antibodies
Antibodies are pivotal in fighting germs and foreign substances. Produced by B cells and composed of protein and sugar, antibodies detect and attach to germs and other potentially toxic substances, eventually destroying them. A key characteristic of antibodies is that each antibody can only attach to an antigen that’s an exact match in much the way that a key can only fit a lock that’s an exact match. This characteristic of antibodies enables them to quickly detect matching germs and initiate a rapid response from the adaptive immune system.