Helper T cell

A helper (or T_H) T cell is a T cell (a type of white blood cell) which has on its surface antigen receptors that can bind to fragments of antigens displayed by the Class II MHC molecules of infected somatic cells.

Once bound to an antigen, the T_H cell proliferates and differentiates into activated T_H cells and memory T_H cells.

• Activated T_H cells secrete cytokines, proteins or peptides that stimulate other lymphocytes; the most common is interleukin-2 (IL-2), which helps B cells differentiate into plasma B cells.
• Memory T_H cells are specific to the antigen they first encountered and can be called upon during the secondary immune response.

Most T_H cells have present on the cell surface the protein CD4, which is attracted to portions of the Class II MHC molecule. This affinity keeps the T_H cell and the target cell bound closely together during antigen-specific activation. T_H cells with CD4 surface protein are called CD4+ T cells.

See also:

• T cell
• White blood cell