Helper T cells (Th cells) are a subset of T cells that play a critical role in the adaptive immune response. These cells are activated by recognizing specific antigens presented by antigen-presenting cells (APCs) in association with major histocompatibility complex (MHC) molecules. Once activated, helper T cells produce cytokines that help to coordinate and regulate the immune response.
There are several different subsets of helper T cells, each with distinct functions and cytokine profiles. The two most well-known subsets are Th1 and Th2 cells.
Th1 cells produce cytokines such as interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) that promote the differentiation of cytotoxic T cells and activate macrophages to kill intracellular pathogens such as viruses and bacteria. Th1 cells also play a role in the pathogenesis of autoimmune diseases by promoting inflammation and tissue damage.
Th2 cells, on the other hand, produce cytokines such as interleukin-4 (IL-4), interleukin-5 (IL-5), and interleukin-13 (IL-13) that promote the differentiation of B cells into plasma cells and the production of antibodies. Th2 cells are important for the immune response against extracellular parasites such as helminths.
In addition to Th1 and Th2 cells, there are several other subsets of helper T cells that have been described, including Th17 cells, regulatory T cells (Tregs), and follicular helper T cells (Tfh).
Th17 cells produce cytokines such as interleukin-17 (IL-17) and interleukin-22 (IL-22) that promote inflammation and recruit neutrophils to sites of infection. Th17 cells are important for the immune response against extracellular bacteria and fungi.
Tregs are a subset of helper T cells that play a critical role in maintaining immune tolerance and preventing autoimmune disease. Tregs produce cytokines such as interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) that suppress the activation and function of other immune cells.
Tfh cells are a subset of helper T cells that are specialized for helping B cells to produce high-affinity antibodies. Tfh cells produce cytokines such as interleukin-21 (IL-21) that promote the differentiation of B cells into memory cells and plasma cells.
Overall, the different subsets of helper T cells play complementary roles in the immune response, coordinating the activities of other immune cells to efficiently eliminate pathogens while avoiding damage to host tissues.