T cell

T cell

A T cell or T lymphocyte is a type of lymphocyte (a subtype of white blood cell) that plays a central role in cell-mediated immunity. T cells can be distinguished from other lymphocytes, such as B cells and natural killer cells, by the presence of a T-cell receptor on the cell surface. They are called T cells because they mature in the thymus from thymocytes (hence T cell).

Types of T cells

There are several different types of T cells, each with a unique function:

• Helper T cells (Th cells) – they assist other white blood cells in immunologic processes, including maturation of B cells into plasma cells and memory B cells, and activation of cytotoxic T cells and macrophages.

• Cytotoxic T cells (Tc cells, CTLs) – they destroy virus-infected cells and tumor cells, and are also implicated in transplant rejection.

• Memory T cells – they remember antigens they have encountered in the past, allowing for a faster response to subsequent encounters.

• Regulatory T cells (Tregs) – they maintain tolerance to self-antigens and prevent autoimmune disease.

• Natural killer T cells (NKT cells) – they share characteristics of both T cells and natural killer cells.

T cell activation

T cells are activated when they are presented with peptide antigens by MHC class II molecules, which are expressed on the surface of antigen-presenting cells (APCs). Once activated, they divide rapidly and secrete small proteins called cytokines that regulate or assist in the active immune response.

Role in disease

T cells play a key role in the immune response to many diseases, including viral infections such as HIV and autoimmune diseases like rheumatoid arthritis and type 1 diabetes. They are also a critical component of the immune response to cancer, and are a target for many new cancer therapies.

See also

• Immune system
• Immunology
• Lymphocyte
• B cell
• Natural killer cell