Capture, Processing, and Presentation of Exogenous Antigen by Essay - 6

Capture, Processing, and Presentation of Exogenous Antigen by Dendritic Cells - Essay Example As the paper stresses B and T cells differ in the manner they recognize antigens. B cells can recognize the antigen through its structure while T cells recognize the same protein only when it has been degraded and presented on the surface of the antigen presenting cell (APC). T cells do not attack free antigens that can be found in the cytosol. In the lymphoid tissues, dendritic cells are considered professional antigen presenting cells (APC) because they are strongest known stimulators of T cells in vivo and in vitro. Thus far, dendritic cells (DC) have only one known function, and that is to present antigens to T cells. Their name was derived dendron, Greek for tree, because of their morphological structure which resembles a tree with many branches or dendrites. From this paper it is clear that the DC arise from myeloid cells in the bone marrow and migrate to peripheral tissues like the skin and mucosa. In these tissues, the immature phenotype of dendritic cells prevail. Immature D C are not yet capable of stimulating T cells. However, the immature DC have receptors that allow them to recognize factors on microbial surfaces allowing them to take up or ingest exogenous antigens through macropinocytosis, endocytosis, and phagocytosis. During macropinocytosis, the dendritic cell membrane forms curved ruffles which fold in to form a pocket enclosing the antigens. The pocket forms a vesicle, called a macropinosome, with 1-5 um diameter, that is filled with extracellular fluid and other molecules including the antigens. The macropinosome then travels into the cytoplasm were it fuses with endosomes and lysosomes. This process occurs constitutively in immature DC and requires the presence of cholesterol. Macropinocytosis occurs in other cells but is only induced by the presence of growth factors.