Antigen presenting cells (APC) are cells of the immune system that engulf dead or foreign cells and other material, which they chop up into smaller sections. APCs present these fragments to T cells, which, in turn, initiate an immune response if the presented molecule stimulates their receptors. In fact, most cells of the human body present antigens to the immune system, but the term, "antigen presenting cell", usually refers to cells of the immune system.

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