Figure 11.2 Enhancement of class II expression by interferon-γ:

11.3 Dendritic cells

As discussed earlier dendritic cells are the major cells of immune system that act as an antigen presenting cell. Dendritic cells are present in the lymphoid organs and epithelial cells of gastrointestinal tract and respiratory tract. All dendritic cells are derived from the bone marrow precursor mononuclear phagocytic cells. Dendritic cells capture the antigen from the skin and epithelial lining of the tissues and enter the lymphatic vessels. Lymph acts as a reservoir of the cell associated as well as free antigen. There are mainly two subsets of dendritic cells.

11.3.1 Conventional dendritic cells

These are also called myeloid dendritic cells. They are the most abundant dendritic cells in the body and responsible for producing a strong T cell immune response. In tissues, they are called Langerhans cells because of its long cytoplasmic process that occupies a large surface area in the epithelial surface which make them highly accessible to the antigens. The surface marker molecules for conventional dendritic cell are CD11c and CD11b. They express high level of Toll like receptor 4, 5, and 8. In addition they secrete high level of tumor necrosis factor and interleukin-6.

11.3.2 Plasmacytoid dendritic cells

They are named so because of their morphology which is similar to plasma cells. The surface marker molecule for plasmacytoid dendritic cell is B220. They express high level of Toll like receptor 7 and 9. They are responsible for the secretion of large amount of type I interferon (α and β) following viral infection.