Immune response: the response made by the host to defend itself against the introduction of foreign substances.Antigen: An antigen is any agent capable of binding specifically to components of immune system, such as BCR and soluble antibodiesImmunogen - A substance that induces a specific immune response.(All immunogens are antigens, but not all antigens are immunogens)Hapten：A hapten is a small molecule which could never induce an immune response when administered by themselves, but which can when attached to a large carrier such as a protein. Haptens have the property of antigencity but not immunogenicity.Antigenicity: The ability of a compound to bind with antibodies or cells of the immune system. This binding is highly specific.Epitope: The portion of the antigen that binds specifically with the binding site of an antibody or a receptor on a lymphocyte. Epitopes determine the specificity of different antigens.Adjuvants: A substance that when mixed with an immunogen, enhances the immune response against the immunogen.Complement：A group of serum proteins involved in the control of inflammation, the activation of phagocytes and the lytic attack on cell membranes. It belongs to the innate immune system, and can be recruited and brought into action by the adaptive immune system.MHC：A cluster of genes on chromosome 6 in humans, encoding cell surface molecules that are polymorphic and that code for antigens which lead to rapid graft rejection between members of a single species which differ at these loci. They play an important role in the immune response, autoimmunity, and reproductive success.Cytokine (CK): Small soluble proteins that mediate immune and inflammatory reactions and are responsible for communications between leukocytes and other cells.Cytokine storm: Under certain circumstances (e.g. septic shock), large amounts of CKs (such as TNF) are produced, they may be active distant from their site of secretion.Leukocyte differentiation antigens: Cell surface molecules which may appear on or disappear from the cell membrane of leukocytes in the different stages of differentiation and activation. They can also be found on other cells.Cluster of differentiation (CD): Cell surface molecules can be recognized by particular monoclonal antibodies. All of the monoclonal antibodies that react with a particular membrane molecule are grouped together as a cluster of differentiationCell adhesion molecules, CAM: A group of proteins involved in adhesion of cell to cell or cell to extracellular matrix (ECM), such as ICAM-1, ICAM-2, ICAM-3, VCAM-1 and PECAM etc.APC：A variety of cell types specialized in the presentation of peptide-MHC to lymphocytes, causing either tolerance or immunity.Somatic hypermutation：Somatic hypermutation (or SHM) is a mechanism inside cells that is part of the way the immune system adapts to the new foreign elements which confront it (for example, microbes).Negative selection:Cells that bind to MHC-Ag on thymic stroma cells (or auto-reactive T cells, ART) will undergo apoptosis. Formation of central immune tolerancePositive selection: Double positive cells that bind, with moderate affinity, to MHC-Ag on thymic stroma cells survive. DP cell acquire MHC restriction though positive selection.Anergy：Anergy is a term in immunobiology that describes a lack of reaction by the body's defense mechanisms to foreign substances, and consists of a direct induction of peripheral lymphocyte tolerance.Regulatory T cell：Regulatory T cells (sometimes known as suppressor T cells) are a specialized subpopulation of T cells that act to suppress activation of the immune system and thereby maintain immune system homeostasis and tolerance to self-antigens.AICD：activation-induced cell death (AICD) recognition and deletion of T lymphocytes that have been induced to proliferate by receptor-mediated activation, preventing their overgrowth.ELISA (Enzyme linked immuno-sorbent assay) An immunological test, using an enzyme as a label to determine presence of target protein.ELISPOT (Enzyme-linked immuno-sorbent spot) A common method for monitoring immune responses in humans and animals. At appropriate conditions the ELISPOT assay allows visualization of the secretary product of individual activated or responding cells.Secondary Antibody: An antibody that binds to primary antibodies or antibody fragments. They are typically labeled with probes that make them useful for detection, purification or cell sorting applications.Artificial active immunization: Administration of an antigen for active production of immunity. Active immunization results in the production of antibodies directed against the infecting agent or its toxic products; it may also initiate cellular immunity.Vaccine: Administration of an antigen for active production of immunity is called artificial active immunization. The agent used for artificial active immunization is called vaccine.Artificial passive immunization:Immunization may be accomplished passively by administering either performed immunoreactive serum (Abs, CKs) or cells.Planned immunization: A rational program of childhood immunization against infectious disease, when many of the most damaging and preventable infections normally appear.。