Question

T cells have to work in a partnership with an Antigen Presenting Cell (APC). Before this can occur, the APC must modify the antigen. Please discuss how this process happens and the major protein that is involved. Be detailed.

Answer 1

An antigen-presenting cell (APC) or accessory cell is a cell that displays antigen complexed with major histocompatibility complexes (MHCs / MHC family of proteins) on their surfaces. This process is known as antigen presentation. Dendritic cells, B-cells and macrophages are the principal antigen-presenting cells for T-cells.

APC cells can process a protein antigen, break it into peptides and present it in conjunction with class II major histocompatibility complex molecules on the cell surface where it may interact with appropriate T-cell receptors. This process is achieved by interacting with APC, which presents an antigen recognized by their T-cell receptor. The APC involved in activating T-cells is usually a dendritic cell. Dendritic cells are one of the principal antigen-presenting cells for T-cells. T-cell can only recognize and respond to antigen that has been processed and presented by cells via carrier molecules like MHC molecules. They cannot recognize and respond to free or soluble antigens. Cytotoxic T-cells can recognize endogenous antigen presented on MHC class I. Helper T-cells can recognize exogenous antigen presented on MHC class II. Most cells in the body can present antigen to CD8+ cytotoxic T-cells via MHC class I; however, the term antigen-presenting cell is often used specifically to describe professional APCs. Such cells express MHC class I and MHC class II molecules and can stimulate CD4+ helper T-cells as well as cytotoxic T-cells.

T-cells recognize these complexes using their T-cell receptors (TCRs). APCs process antigens and present them to T-cells.