Helper T (TH) cells provide help to other cells in the immune response by recognizing toxin or other foreign substances (antigens) which induce an immune response in the body. The Helper T cells then secrete chemicals called cytokines that activate T cells and B cells. These chemicals stimulate the immune response. They help suppress or regulate immune responses and are vital to human immune responses. DIAGRAM: Antigen-presenting cells (APCs) present antigen on their MHC molecules (MHC2). Helper T cells recognize these, with the help of their expression of CD4 co-receptor (CD4+). The activation of a resting helper T cell causes it to release cytokines and other stimulatory signals (green arrows) that stimulate the activity of macrophages, killer T cells and B cells, the latter producing antibodies. The stimulation of B cells and macrophages succeeds a proliferation of T helper cells. Helper T cells are called the "conductors" of the immune system because they coordinate activity like the conductor of an orchestra. Helper T (TH) cells are critical to coordinating the activity of the immune response. RESOURCES: Cardiff University Wikipedia