In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.
A cytotoxic T cell (also known as TC, cytotoxic T lymphocyte, CTL, T-killer cell, cytolytic T cell, CD8+ T-cell or killer T cell) is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected by intracellular pathogens (such as viruses or bacteria), or cells that are damaged in other ways.
The major histocompatibility complex (MHC) is a large locus on vertebrate DNA containing a set of closely linked polymorphic genes that code for cell surface proteins essential for the adaptive immune system. These cell surface proteins are called MHC molecules.
An oligosaccharide is a saccharide polymer containing a small number of monosaccharides. Oligosaccharides can have many functions including cell recognition and cell adhesion.
Antigen processing, or the cytosolic pathway, is an immunological process that prepares antigens for presentation to special cells of the immune system called T lymphocytes. It is considered to be a stage of antigen presentation pathways. This process involves two distinct pathways for processing of antigens from an organism's own (self) proteins or intracellular pathogens, or from phagocytosed pathogens ; subsequent presentation of these antigens on class I or class II major histocompatibility complex (MHC) molecules is dependent on which pathway is used. Both MHC class I and II are required to bind antigens before they are stably expressed on a cell surface. MHC I antigen presentation typically involves the endogenous pathway of antigen processing, and MHC II antigen presentation involves the exogenous pathway of antigen processing. Cross-presentation involves parts of the exogenous and the endogenous pathways but ultimately involves the latter portion of the endogenous pathway.
CD1 is a family of glycoproteins expressed on the surface of various human antigen-presenting cells. CD1 glycoproteins are structurally related to the class I MHC molecules, however, in contrast to MHC class 1 proteins, they present lipids, glycolipids and small molecules antigens to T cells. Both αβ and γδ T cells recognise CD1 molecules.
In immunology, central tolerance is the process of eliminating any developing T or B lymphocytes that are autoreactive, i.e. reactive to the body itself. Through elimination of autoreactive lymphocytes, tolerance ensures that the immune system does not attack self peptides. Lymphocyte maturation occurs in primary lymphoid organs such as the bone marrow and the thymus. In mammals, B cells mature in the bone marrow and T cells mature in the thymus.
CD1D is the human gene that encodes the protein CD1d, a member of the CD1 family of glycoproteins expressed on the surface of various human antigen-presenting cells. They are non-classical MHC proteins, related to the class I MHC proteins, and are involved in the presentation of lipid antigens to T cells. CD1d is the only member of the group 2 CD1 molecules.
Antigen presentation is a vital immune process that is essential for T cell immune response triggering. Because T cells recognize only fragmented antigens displayed on cell surfaces, antigen processing must occur before the antigen fragment, now bound to the major histocompatibility complex (MHC), is transported to the surface of the cell, a process known as presentation, where it can be recognized by a T-cell receptor. If there has been an infection with viruses or bacteria, the cell will present an endogenous or exogenous peptide fragment derived from the antigen by MHC molecules. There are two types of MHC molecules which differ in the behaviour of the antigens: MHC class I molecules (MHC-I) bind peptides from the cell cytosol, while peptides generated in the endocytic vesicles after internalisation are bound to MHC class II (MHC-II). Cellular membranes separate these two cellular environments - intracellular and extracellular. Each T cell can only recognize tens to hundreds of copies of a unique sequence of a single peptide among thousands of other peptides presented on the same cell, because an MHC molecule in one cell can bind to quite a large range of peptides. Predicting which antigens will be presented to the immune system by a certain MHC/HLA type is difficult, but the technology involved is improving.
MHC Class II molecules are a class of major histocompatibility complex (MHC) molecules normally found only on professional antigen-presenting cells such as dendritic cells, mononuclear phagocytes, some endothelial cells, thymic epithelial cells, and B cells. These cells are important in initiating immune responses.
Leukocyte immunoglobulin-like receptor subfamily B member 1 is a protein that in humans is encoded by the LILRB1 gene.
HLA class II histocompatibility antigen, DM beta chain is a protein that in humans is encoded by the HLA-DMB gene.
HLA class II histocompatibility antigen, DM alpha chain is a protein that in humans is encoded by the HLA-DMA gene.
T-cell surface glycoprotein CD1e, membrane-associated is a protein that in humans is encoded by the CD1E gene.
HLA class II histocompatibility antigen, DX beta chain is a protein that in humans is encoded by the HLA-DQB2 gene.
Major histocompatibility complex class I-related gene protein (MR1) is a non-classical MHC class I protein, that binds vitamine metabolites produced in certain types of bacteria. MR1 interacts with mucosal associated invariant T cells (MAIT).
CD1a is a human protein encoded by the CD1A gene.
Vincenzo Cerundolo was the Director of the Medical Research Council (MRC) Human Immunology Unit at the University of Oxford, at the John Radcliffe Hospital and a Professor of Immunology at the University of Oxford. He was also a Supernumerary Fellow at Merton College, Oxford. He was known for his discoveries in processing and presentation of cancer and viral peptides to T cells and lipids to invariant NKT cells. Cerundolo died of lung cancer on 7 January 2020.
Cd1-restricted T cells are part of the unconventional T cell family, they are stimulated by exposure to CD1+ antigen presenting cells (APCs). Many CD1-restricted T cells are rapidly stimulated to carry out helper and effector functions upon interaction with CD1-expressing antigen-presenting cells. CD1-restricted T cells regulate host defence, antitumor immunity and the balance between tolerance and autoimmunity.
Group 1 CD1-restricted T cells are a heterogeneous group of unconventional T cells defined by their ability to recognize antigens bound on group 1 CD1 molecules with their TCR. Natural killer T (NKT) cells are a similar population with affinity to CD1d. Both groups recognize lipid antigens in contrast to the conventional peptide antigens presented on MHC class 1 and 2 proteins. Most identified T-cells that bind group 1 CD1 proteins are αβ T cells and some are γδ T cells. Both foreign and endogenous lipid antigens activate these cells.
