What is the function of T-helper cells?

T-helper cells are a kind of lymphocyte that are a key part of the adaptive immune system. The adaptive immune system is largely coordinated by T cells, of which there are several types, and B cells, the other kind of lymphocyte. T cells originate in the Thymus, while B cells originate in the Bone marrow. Once mature, the T cells affect the cell-mediated response to pathogens, whereas B cells remain in the bone marrow and produce antibodies, as part of the humoural response. T cells are activated once a complementary antigen is presented to them by an antigen presenting cell, such as a macrophage, which has taken and presented it from a pathogen. The T cell then begins to clone itself, before these clones go on to specialise into the different types of T cell, all of which are specific to the antigen. One of these types is the T-helper cell, which helps develop the B cells to respond to the specific antigen and augment the other killer T cells and phagocytes in their efforts to fight the infection. It does this by releasing cytokines, a kind of chemical messenger, that signals the other cells.