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 Antigen-Presenting Cells
 Macrophages
 Dendritic Cells
 Langerhans Cells

Antigen-processing cell (APC)
Antigen-presenting cell, Accessory Cells

T lymphocytes are part of the immune system involved in identifying antigens . However, for an antigen to be recognised by a T-lymphocyte, it must be first processed and "presented" in a form the antigen can recognise. This is the function of an APC, also referred to as accessory cells . The process by which this takes place is the following :

  1. An APC (see below for the principal different types) engulfs an antigen.
  2. Enzymes in the APC break down the antigen into smaller fragments.
  3. These fragments are transported to the surface of the APC, bound with class II MHC (major histocompatibility complex) molecules.
  4. A T-cell receptor can now recognise the antigen linked with the MHC and thus binds to it.

Examples of Antigen-processing cells include:
  • Macrophages
    These are large white blood cells that ingest antigens and other foreign substances. Each macrophage contains packets of chemicals and enzymes, which digest the ingested antigen or microbe.

  • Dendritic Cell (DC)
    Follicular Dendritic Cell (FDC)

    Dendritic cells are the principle APC involved in primary immune responses . Their major function is to obtain antigen in tissues, migrate to lymphoid organs and activate T cells . Cell required for, but not actually mediating, a specific immune response.

  • Langerhans Cell
    Langerhans Cells are dendritic cells specific to the skin.
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      http://www.hon.ch/Library/Theme/Allergy/Glossary/apc.html Last modified: Fri Jun 28 2002