Antigen Presenting Cells

Antigen-presenting cells, also known as APCs, process foreign antigens, such as fragments from pathogens, for recognition by T cells.

When an APC engulfs an antigen, it breaks it down into fragments and combines them with the major histocompatibility complex or MHC molecules.

This antigen-MHC complex is then inserted into the plasma membrane of the APC for presentation to a naive T cell.

The dendritic cells, macrophages, and B cells are the major types of APCs in the body.

They efficiently internalize antigens by phagocytosis, as seen in dendritic cells and macrophages, or by receptor-mediated endocytosis in B cells.

Dendritic cells are highly efficient and mobile APCs. They are predominantly found in tissues that encounter antigens first, such as the skin, mucosal surfaces, and lymphoid organs.

On the other hand, all tissues have macrophages that present antigens to T cells and release cytokines for T cell activation.

Lastly, B cells present antigens to activate T cells. The activated T cells, in turn, provide signals for final B cell activation.