Antigen presenting cells

Antigen Presenting Cells (or APCs) are involved in the immune system and activation of T-cells. APCs cover several cell types including dendritic cells, macrophages and B cells. They express MHC II molecules which bind small peptides from a pathogen to present it to T cells.

Dendritic cells

Dendritic cells have long projections away from the main cell body similar to the dendrites found on the nerve cell (hence the name). Thes cells begin as all cells in the immune system do, they are created by differentiation of pluripotent stem cells found in the bone marrow. Immature dendritic cells leave the bone marrow travelling in the bloodstream into tissues, as they travel they perform macropinocytosis to take in large amounts of ECF. Dendritic cells do have the ability to digest pathogens they encounter but their main function in the immune system is to activate virgin T-cells by presenting any foreign molecules that have been picked up on the cell's travels. This gives a vital link between the innate and adaptive immune response.

Macrophages

Macrophages perform phagocytosis upon any invading molecule/cell that it recognises, the digested material is then presented on its cell surface to activate T-cells to destroy any more of the invader is present. Macrophages are mature cells that reside in most tissues, some tissues have specialised versions of macrophages, and in the lymphoid organs.