Dendritic cells have a major role as an antigen-presenting cell, meaning that they identify foreign antigens and show them to the immune system to enact an immune response. To facilitate this process, dendritic cells are found in tissues throughout the body, and use their long cell processes to maximize their surface area to increase the chance of encountering an antigen.
Dendritic cells use many pattern recognition receptors, including mannose receptors and TLRs to identify and bind antigens. Once a dendritic cell has captured an antigen, it expresses chemokine receptors similar to T lymphocytes. This allows the dendritic cell to migrate along the chemotactic gradient towards the perifollicular zones of local lymph nodes, where the T lymphocytes are found. After entering a lymphoid tissue, the dendritic cells express a high number of MHC class II molecules, which they use to show the antigens they find to T lymphocytes. This process is further discussed in lymphocyte activation.
There are actually many types of dendritic cells, which are summarized below.
| Type of Dendritic Cell | Location | Function |
|---|---|---|
| Langerhans cells | Skin, mucous membranes | Immune surveillance and antigen presentation |
| Interstitial dendritic cells | Most major organs | Immune surveillance and antigen presentation |
| Interdigitating dendritic cells | Thymus and T lymphocyte areas of lymphoid tissue | Negative selection in thymus Peripheral tolerance in lymphoid tissues |
| Circulating dendritic cells | Blood | Immune surveillance and antigen presentation |
| Follicular dendritic cells | Lymphoid follicles | Development and maintenance of memory B lymphocytes |
A brief note on follicular dendritic cells:
These cells are considered a unique type of dendritic cell, as they do not have antigen-presenting functions. Instead, they express receptors for immunoglobulins and C3b, to trap antigen bound to antibodies and complement. They then present these antigens to B cells, to produce memory cells.
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