The bone marrow is the location where immature B and T cells form. They develop from the stem cells located in the bone marrow.
B and T cells are formed in the bone marrow from stem cells in a process called haematopoiesis.
B cells reach a semi-mature level in the bone marrow before traveling to the spleen and becoming a fully-functional mature B cell.
The thymus is an immune system organ primarily involved in the maturation of T cells. It is located in front of the heart and behind the sternum.
T cells are tested for self response in the thymus. Autoimmunity is when the body's immune cells attack the body itself, and to avoid this, T cells are tested for whether they attack the body's proteins and antigens.
T cells reach maturity in the thymus and are ready to destroy infected cells (cytotoxic and natural killer T cells) or assist by activating B and killer T cells (helper T cells).
The lymph nodes are the garrisons of immunity cells. They are distributed throughout the body and linked by lymphatic vessels. They are filters and traps for foreign molecules.
In the lymph nodes, mature B and T cells monitor the lymph circulating through for pathogens. B cells respond through antibody production, while cytotoxic and killer T cells destroy the pathogens.
The spleen is analogous to the large lymph nodes for blood filtration. It holds a reserve of blood in case of hemorrhage and filters red blood cells. In the immune system, it serves as a site of B and T cell activity.
In the spleen, mature B and T cells look for pathogens and bind to any free floating antigens. They then trigger the humoral adaptive immune response and the cell-mediated adaptive immune response.
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