Which cell is known as antigen presenting cell?

Antigen presenting cells (APCs) are cells of the immune system that capture, process and present antigens (pieces of foreign substances) on their surface to be recognised by T cells. The main types of APCs include:

1. Dendritic cells: These are the most potent APCs and are found in tissues throughout the body. They capture and process antigens and then migrate to the lymph nodes where they present the antigens to T cells.

2. Macrophages: These are large phagocytic cells that are found in tissues and the blood. They engulf and digest foreign particles and present antigens to T cells.

3. B cells: In addition to their role in producing antibodies, B cells can also function as APCs. They present antigens to T cells in a process called "B cell antigen presentation".

4. Follicular dendritic cells (FDCs): These are specialised dendritic cells that are found in the germinal centres of lymph nodes. They capture and retain antigens on their surface, allowing B cells to interact with them and differentiate into memory B cells and plasma cells.

These APCs play a crucial role in initiating and regulating immune responses by presenting antigens to T cells and activating them to mount an immune response against foreign pathogens or abnormal cells.