An Antigen Presenting Cell (APC) is a type of immune cell that plays a crucial role in the body's defense against pathogens. APCs capture, process, and present antigens—substances that can provoke an immune response—on their surface. This presentation is essential for activating T cells, which are vital for orchestrating the immune response. There are several types of APCs, including dendritic cells, macrophages, and B cells. Each of these cells has unique functions but all share the ability to present antigens to T cells. This interaction helps the immune system recognize and respond effectively to infections and other foreign substances.