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 trigger an immune response—on their surface. This presentation is essential for activating T cells, which are vital for orchestrating the immune response. Common types of APCs include dendritic cells, macrophages, and B cells. These cells help the immune system recognize and respond to foreign invaders, such as bacteria and viruses. By presenting antigens, APCs facilitate communication between different immune cells, ensuring a coordinated and effective immune response.