T-lymphocytes originate in the bone marrow and mature in the thymus. T-lymphocytes circulate in the blood and lymph system, they may also be found in tissues. They recognise antigens through a unique surface receptor called the T Cell Receptor (TCR).

T-lymphocytes promote an immune response when they recognise an antigen that is presented by another cell such as a dendritic cell, macrophage or other body cells that has become infected. T-lymphocytes randomly bind to antigens presented by these cells until they encounter the antigen they specifically respond to. Once this happens a process called clonal expansion occurs, with the originally activated T-lymphocyte producing multiple copies of itself, known as clones. These clones circulate throughout the body looking for signs of infection or inflammation and carry out a range of different roles within the immune response.

3D rendering of a T-lymphocyte Lymphocytes are characterised by a single large nucleus, shown here in orange in this 3D rendering of a T-lymphocyte.

Some T-lymphocytes (CD4+) help B-lymphocytes produce antibodies to neutralise a threat, while others (CD8+) can directly kill cells that have become infected or cancerous. Regulatory T-lymphocytes play an important role in preventing the body's immune response from attacking itself. Th17 lymphocytes play an important role in the defence against fungal infections.



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