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Antigen presentation stimulates immature T cells to become either mature "cytotoxic" CD8+ cells or mature "helper" CD4+ cells. An antigen-presenting cell (APC) or accessory cell is a cell that displays an antigen bound by major histocompatibility complex (MHC) proteins on its surface; this process is known as antigen presentation.
Because T cells recognize only fragmented antigens displayed on cell surfaces, antigen processing must occur before the antigen fragment can be recognized by a T-cell receptor. Specifically, the fragment, bound to the major histocompatibility complex (MHC), is transported to the surface of the antigen-presenting cell, a process known as ...
The discussion that follows now concerns alpha/beta T cells. The TCR (of αβ T-cells) binds a bimolecular complex displayed at the surface of some other cells called an antigen-presenting cell (APC). This complex consists of: a fragment of an antigen lying within the groove of a histocompatibility molecule. The complex has been compared to a ...
A dendritic cell (DC) is an antigen-presenting cell (also known as an accessory cell) of the mammalian immune system. A DC's main function is to process antigen material and present it on the cell surface to the T cells of the immune system. They act as messengers between the innate and adaptive immune systems. [1]
Cross-presentation is the ability of certain professional antigen-presenting cells (mostly dendritic cells) to take up, process and present extracellular antigens with MHC class I molecules to CD8 T cells (cytotoxic T cells).
During an immune response, professional antigen-presenting cells (APCs) endocytose antigens (typically bacteria or viruses), which undergo processing, then travel from the infection site to the lymph nodes. Typically, the APC responsible is a dendritic cell.
CD4 is a co-receptor of the T cell receptor (TCR) and assists the latter in communicating with antigen-presenting cells. The TCR complex and CD4 bind to distinct regions of the antigen-presenting MHC class II molecule. The extracellular D 1 domain of CD4 binds to the β2 region of MHC class II.
Function of T helper cells: Antigen-presenting cells present antigens on their Class II MHC molecules . Helper T cells recognize these by expressing the CD4 co-receptor . The activation of a resting helper T cell causes it to release cytokines and other signals (green arrows) that stimulate the activity of macrophages , killer T cells , and B ...