| Antigen Presenting Cell |
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TYPES There are three main types of professional antigen-presenting cells: These APCs are very efficient at Phagocytosis , which allows them to present exogenous as well as internal antigens. For the purpose of effectively stimulating naive T cells, APCs possess co-stimulatory molecules: cell-surface molecules that deliver essential signals to T cells, allowing the T cells to become activated and mature into fully-functional forms. Dendritic cells, and to a lesser extent macrophages, have the broadest range of antigen presentation, and are probably the most important APC. Activated DCs are especially potent TH cell activators because, as part of their composition, they express Co-stimulatory molecules such as B7 . B cells, which express antibody, can very efficiently present the antigen to which their antibody is directed, but are inefficient APC for most other antigens. As well, there are specialized cells in particular organs (e.g., Microglia in the brain, Kupffer Cell s in the liver) derived from macrophages that are also effective APCs. INTERACTION WITH T CELLS After dendritic cells or macrophages swallow pathogens, they usually migrate to the s that flow in the Blood and Lymph vessels "draw" the APCs to the lymph nodes. During the migration, DCs undergo a process of maturation; In essence, they lose most of their ability to further swallow pathogens, and they develop an increased ability to communicate with T cells. Enzymes within the cell digest the swallowed pathogen into smaller pieces containing Epitopes , which are then presented to T cells using MHC. Recent research indicates that only certain epitopes of a pathogen are presented because they are immunodominant, possibly as a function of their binding affinity to the MHC. The stronger binding affinity allows the complex to remain kinetically stable long enough to be recognized by T cells. |
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