The bone marrow is where immature B and T cells form. They develop from stem cells located in the bone marrow.
B and T cells are formed in the bone marrow from stem cells during a process called hematopoiesis.
B cells reach a semi-mature level in bone marrow before traveling to the spleen to become fully-functional mature B cells.
The thymus is an immune system organ primarily involved in 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 and cells. A functional thymus tests T cells to determine if they will 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 filter and trap foreign pathogens and molecules.
In lymph nodes, mature B and T cells monitor circulating lymph for pathogens. B cells respond to pathogens by producing antibodies, and 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 and filters red blood cells. In the immune system, it serves as a site for B and T cell activity.
In the spleen, mature B and T cells look for pathogens and bind to any free floating antigens. With antigens from pathogens, they trigger the humoral-adaptive and cell-mediated adaptive immune responses.
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