Helper T cells are recognised by being positive for the cluster of differentiation antigen CD4. They may therefore be referred to as CD4+ cells.
Helper T cells, once stimulated by foreign antigen bound to MHC class II complexes, release cytokines which activate macrophages and stimulate B cells to divide, differentiate and produce antibodies.
Helper T cells may be further differentiated according to the cytokines they produce into type 1 helper T cells (Th1) and type 2 helper T cells (Th2). Th3 T cells have also been described.
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