T helper cell

T helper cells (also known as Th cells) are a type of T cell that play a crucial role in the immune system, particularly in the adaptive immune system. They help the activity of other immune cells by releasing T cell cytokines. These cells help suppress or regulate immune responses. They are essential in B cell antibody class switching, in the activation and growth of cytotoxic T cells, and in maximizing bactericidal activity of phagocytes such as macrophages.

Classification

Based on function, T helper cells can be classified into several subsets, including Th1, Th2, Th17, Tfh, and Treg cells. Each subset is distinguished by their cytokine production and function.

Function

T helper cells recognize antigens presented by antigen-presenting cells (APCs) in the context of major histocompatibility complex (MHC) class II molecules. Once activated, they divide rapidly and secrete small proteins known as cytokines that regulate or assist in the active immune response.

Activation

The activation of a T helper cell involves its interaction with an antigen-presenting cell. This interaction involves a simultaneous engagement of the T cell receptor and a co-receptor (CD4) on the T helper cell with the MHC class II molecule and the antigenic peptide, respectively, on the APC.

Role in disease

T helper cells play a central role in several immune-related diseases. For example, they are the primary target of HIV infection, and their depletion leads to the immunodeficiency characteristic of AIDS. In autoimmune diseases such as Multiple sclerosis, T helper cells appear to play a role in mediating pathological damage.

See also

• CD4+ T cells and antitumor immunity
• T cell receptor
• Cytotoxic T cell

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  Activation of T and B cells
• 
  T-dependent B cell activation
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  Antigen presentation
• Lymphocyte activation
  Lymphocyte activation