Where are T-cells located?

Depending on their development stage, T-cells are located in different parts of the body – primarily the bone marrow, thymus, and lymph tissue or blood stream. 

Bone Marrow

T-cells originate as hematopoietic stem cells in the spongy tissue in the marrow, a spongy tissue found inside the bone. These cells have the potential to differentiate into various blood cell types.

Thymus Gland

Newly-formed T-cells move from the bone marrow to the thymus, a gland located in the upper mid-chest area. Here, the immature T-cells, known as thymocytes, undergo a crucial maturation process, starting with a rigorous testing to ensure they can correctly bind to Major Histocompatibility Complex (MHC) while refraining from attacking the body's healthy cells. In addition, they also receive the appropriate receptor type - CD4 for helper T-cells or CD8 for cytotoxic T-cells. Only T-cells that pass these stringent tests are allowed to enter the circulation and travel throughout the body.

Lymph Tissue And Bloodstream

Once fully matured, T-cells migrate to various tissues and organs within the lymphatic system. They can be located in the lymph nodes, spleen, tonsils, and the bloodstream, where they remain on standby awaiting signals to mobilize and defend the body against potential threats.