by Jason Wasserman MD PhD FRCPC
May 25, 2022
T cells (also called T lymphocytes) are a type of white blood cell and a part of the immune system. T cells come from hematopoietic stem cells found in the bone marrow. These cells are called stem cells because they give rise to all the cells in the blood and immune system. T cells then travel to an organ called the thymus where they develop further before entering the bloodstream. Many T cells are found in lymphoid organs such as lymph nodes which are found throughout the body. Large numbers of T cells can also be found in an area of inflammation caused by infection or injury.
T cells contribute to a process called the adaptive immune response. The adaptive immune response is important for protecting the body against infections. T cells help other types of immune cells such as B cells to recognize and fight off infections. T cells can also directly kill cells that have become infected by a virus.
Common markers used to identify T cells include CD3 and CD5. Additional markers such as CD4 and CD8 can be used to identify subtypes of T cells such as helper T cells and cytotoxic T cells. Pathologists perform tests such as immunohistochemistry and flow cytometry to see T cells making CD3, CD5, CD4, and CD8.
Most cancers made up of T cells are part of a group of cancers called lymphoma. The most common types of T cell lymphoma are extranodal NK/T cell lymphoma, primary cutaneous T cell lymphoma, peripheral T cell lymphoma, and anaplastic T cell lymphoma.