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| Question | Answer |
| Adaptive immunity | A form of immunity that is specifically stimulated by antigen, resulting in clonal selection of antigen-relevant lymphocytes. This provides a more potent immune response to support non-specific innate immunity. The adaptive immune response generates immunological memory. Also ‘acquired immunity’. |
| Immunoglobulin | A general term for all antibody molecules. |
| Th1 | A helper T lymphocyte that preferentially produces IFN-γ and stimulates cellular immunity. CD4+ |
| Th2 | A helper T lymphocyte that preferentially produces IL-4, IL-5, IL-9 and IL-13 and stimulates humoral immunity. CD4+ |
| Perforin | A molecule released from a cytotoxic cell that polymerises to form a pore within the cell membrane of the target cell, allowing the influx of other cytotoxic molecules, ions and water (cell lysis) |
| Adjuvant | A substance which results in a specific increase in the immunogenicity of a vaccine component; enhances the immune response. Traditional adjuvants are non-specific in their effect or they may have a ‘depot effect’ causing sustained release of antigen. Modern adjuvants may have a more targeted effect on the immune response (e.g. cytokine adjuvants, CpG motifs). |
| Langerhans cells | A type of dendritic APC located within the epidermis. |
| Microglial cells | A type of macrophage located within the brain. |
| Kupffer cells | A type of macrophage located within the liver. |
| Immunisation | Administration of an antigen to a live host with the purpose of inducing an immune response in the host |
| Hypersensitivity | All involve mostly the same effector mechanisms: inflammation, complement, mast cells and secondary cells. Major difference is in the mechanism of initiation. Types I-III are antibody-mediated responses; type IV has cell-mediated responses. Type I: immediate; types II+III: intermediate; type IV: delayed. |
| CD3 | All T cells |
| Autoimmune reaction | An immune response to self-antigen resulting in tissue pathology and autoimmune disease. |
| APCs | Antigen Presenting Cells: Dendritic cells, activated macrophages, B cells (pinocytosis). |
| Endogenous antigens | Antigens produced within the cytoplasm of an APC (i.e. self-antigen or viral antigen). |
| Peri-arteriolar lymphoid sheath | Area of white pulp of the spleen in which T lymphocytes reside. In three dimensions, the T cells form a cylindrical sheath that surrounds an arteriolar blood vessel. |
| Ileal Peyer's Patches | Areas of organised but unencapsulated lymphoid tissue within the small intestinal mucosa. |
| Myeloid cells | Attack cells, granulocytes and monocytes. |
| CD19 | B cells |
| B cells | B cells (CD19+) develop in bone marrow and express surface immunoglobulin. Through activation, B cells are differentiated into memory cells or plasma cells. |
| Antigen processing | Breakdown of antigen to small peptide components within the cytoplasm of an APC via either the endogenous or exogenous pathway. |
| Opsonisation | Coating of a particle with antibody and/or complement to enhance the effectiveness of phagocytosis. |
| Membrane Attack Complex (MAC) | Collection of terminal pathway complement components that form a channel through the membrane of a target cell and lead to osmotic lysis. |
| Major Histocompatibility Complex | Complex of genes encoding molecules that mediate histocompatibility and antigen presentation. Highly polymorphic and broadly divided into class I, II and III genes. |
| Antibody dependant cell cytoxicity (ADCC) | Cytotoxic destruction of a target cell coated by antibody that is recognized by an Fc receptor on the surface of the cytotoxic cell. |
| CD8 | Cytotoxic T cells |
| Memory cells | Differentiated B cells. |
| Haematopoiesis | Differentiation from haemopoietic stem cells into immune cells (Lymphoid + Myeloid cells mainly) |
| Effector function | Effector cell: cell that actively participates in an immune response (e.g. by producing antibody or destroying a target cell via cytotoxicity). |
| Granzymes | Enzymes released by NK cells which damage target cells |
| Antigen presentation | Expression of small peptide fragments derived from an antigen (by antigen processing) on the surface of an APC within the binding groove of an MHC Class I or II molecule. |
| Exogenous antigens | External antigen taken up by an APC. |
| MHC Class I | Found on the surface of all nucleated ‘self’ cells. Long α chain (3 domains), short β chains (1 domain) |
| Fab region | Fragment antigen binding site. Antigen binding site at the N terminal end of the immunoglobulin molecule. |
| Fc region | Fragment crystallisable. Heavy chains at the C terminal end of the immunoglobulin molecule. |
| Basophil | Granulocyte, smaller than a mast cell. |
| T helper cells | Help B cells divide, differentiate and produce antibody. Recognise MHC Class II. CD4+. Central to the immune response |
| Vaccination | Immunisation for veterinary (or public) health purposes: induction of an adaptive immune response with immunological memory by deliberate exposure to an antigen. Typically the antigen is an attenuated or killed pathogen and the process of vaccination induces an immune response that can protect the individual from field exposure to virulent pathogen. |
| Humoral immunity | Immunity mediated by antibody. |
| IgA | Immunoglobulin A – α chain. Found in mucous secretions, e.g. saliva, bronchial mucous |
| IgD | Immunoglobulin D – δ chain. On surface of naïve differentiating B cells; binds to basophils |
| IgE | Immunoglobulin E – ε chain. Active in allergic responses and helminth infections |
| IgG | Immunoglobulin G – γ chain. Bind complement & effector cells (Macrophages/neutrophils/eosinophils). Birds/reptiles/amphibians have IgY instead of IgG. Primary defence against extracellular threats (toxins, bacteria) – through neutralisation |
| IgM | Immunoglobulin M – µ chain. Original antibody found on B cells before antigen exposure. Agglutinates red blood cells |
| BCR | Immunoglobulin receptor for antigen on the surface of a B lymphocyte. (B cell receptor) |
| Drug action on immunophilins | Immunosuppressant given to graft recipients. Cyclosporin suppresses function of T cells, prevents rejection by CD8+ Tc cells. |
| Glucocorticoids | Immunosuppressant given to graft recipients. Suppresses cytokine production by T cells, prevents inflammation driven by T cells, and thus suppresses graft rejection. |
| Clonal expansion | Increase in numbers for stronger attack. |
| IFN | Interferon: a type of cytokine. The type I interferons (e.g. IFN-α, IFN-β) are antiviral molecules, whereas type II interferon (IFN-γ) is a key immunological molecule. |
| IL | Interleukins: a type of cytokine secreted by one leucocyte that binds a receptor expressed by another leucocyte. |
| Phagocytosis | Internalisation of a particle by a phagocytic cell (e.g. neutrophil or macrophage). |
| Mast cell | Larger than basophils, mast cells are non-phagocytic granulocytes which bind allergens (IgE) and initiate/increase inflammation. |
| Plasma cells | Late stage of differentiation of a B lymphocyte. The cell that synthesises and secretes immunoglobulin. |
| Afferent lymph | Lymph draining from tissue to the regional lymph node. Carry to lymph node (A for Arrives) |
| Lymph | Lymph is the fluid bathing all tissues. |
| Efferent lymph | Lymphatic vessel draining lymph from a lymph node to the common thoracic duct. Carry away from lymph node (E for Exits) |
| Recognition cells | Lymphoid cells |
| Natural Killer cells | Lymphoid cells with granular cytoplasm that mediates cytotoxicity of targets via NK-cell receptors or Fc receptors (see also ADCC). CD16+ |
| Dendritic cells | Major APC for a primary immune response. Undertakes antigen capture, processing and presentation to T cells. Characteristic morphology with cytoplasmic dendrites. |
| CD25 | Majority of T reg cells |
| T cytotoxic cells | Mediates destruction of a specific target cell: binds and kills pathogens and infected or cancer cells. Recognise MHC Class I. CD8+. Primary defence against intracellular threats (viruses, bacteria). Kill via perforin, granzymes and TNF-α |
| Chemotaxis | Migration of a leucocyte along a chemotactic gradient of increasing concentration of a chemoattractant. |
| Attack cells | Myeloid cells |
| Macrophage | Myeloid monocyte which breaks up antigens by phagocytosis. Kill via TNF-α, nitric oxide, superoxide radicals, hydrogen peroxide, cationic proteins, hydrolytic enzymes, ADCC |
| CD16 | Natural killer cells |
| Granulocytes | Neutrophils, eosinophils, mast cells, basophils. Myeloid cells. |
| Cluster of Differentiation | Nomenclature used to define immune cell surface molecules. Activation needed to produce certain CDs. Not expressed by all cells. Many are receptors for cytokines or ligands for binding to cells/antigens. |
| Epithelial barrier | One of the 4 barriers of primary defence in the innate immune system. Includes skin and mucous membranes. Normal skin microflora compete with incoming bacteria; skin sebum has antimicrobial effects and prevents hair and skin from drying out. Mucous membranes feature cilia (respiratory), villi (gut), mucous goblet cells; microflora in the gut competes with pathogens; peristalsis suppresses colonisation. |
| Physiological barrier | One of the 4 barriers of primary defence in the innate immune system. Includes temperature (fever induction), pH (acidity of stomach), and chemical mediators. Chemical mediators damage pathogens and assist phagocytes to engulf pathogens, and include enzymes (e.g. lysozyme in secretions/tears), peptides (e.g. ?-defensins, Paneth cells in skin and mucosa), cytokines, immune hormones, interleukins, interferons, tumour necrosis factor, acute-phase proteins (e.g. C-reactive protein helps phagocytosis; haptoglobin sequesters iron), and complement serum proteins. |
| Phagocytic barrier | One of the 4 barriers of primary defence in the innate immune system. Phagocytes are white cells that engulf pathogens. |
| Inflammatory barrier | One of the 4 barriers of primary defence in the innate immune system. Tissue damage (e.g. abrasions, cuts, wounds) is a breach of anatomical barriers. Damaged cells release chemical factors. Vasodilation increases capillary permeability and allows phagocytes to enter tissue. Chemotaxis attracts phagocytes to infection sites (macrophages, neutrophils) and extravasation occurs (migration of phagocytes via capillaries to damaged tissue). |
| Neutrophil | Phagocytic cell: most abundant granulocyte (90% of granulocytes) |
| Antibody | Protein that binds specifically to an antigen. Antibodies are secreted by plasma cells and can bind to pathogens to target them for removal. Each antibody has unique antigen binding capacity, but shares structure with other antibodies or immunoglobulins. |
| Recombinant (vaccine) | Pure source of protein produced in vitro by inserting a gene into a vector (e.g. bacterial, insect or mammalian cell). The gene is expressed and the protein released from the cells into the culture medium. Such recombinant proteins can form the basis for vaccines. |
| Lymphoid cells | Recognition cells of antigens or epitopes; small-medium cells with large nuclei. T cells, B cells, NK cells, Plasma cells. |
| Secondary lymphoid tissue | Responsible for cell storage and antigen contact. |
| Primary lymphoid tissue | Responsible for T and B cell production. |
| MHC Class II | Same size α chain and β chain (2 domains) |
| Clonal selection model | Selection for activation of antigen-relevant lymphocytes from the entire repertoire on exposure to antigen. |
| Complement | Series of plasma proteins which when activated interact sequentially, forming a self-assembling enzymatic cascade and generating biologically active molecules that mediate a range of end processes. Activated by Classical, Alternate or Lectin pathways. Mediate inflammation: smooth muscle contraction, increased vascular permeability and plasma leakage, mast cell degranulation. Opsonins – promote phagocytosis by macrophages and neutrophils. |
| Lymph nodes | Site of antigen and immune cell interaction: B cells in follicles, T cells in paracortex, densely packed. |
| Paratope | Site of specific antigen binding on an antibody |
| Epitope | Site on an antigen that may be recognised by an antibody or TCR. The nature of epitopes bound by these two types of receptor is different. Also called an antigenic ‘determinant’. |
| Cytokines | Soluble protein secreted by one cell that binds to a specific cytokine receptor expressed by another cell, leading to a change in function of the target cell. Cytokines are considered intercellular messengers of the immune system. A generic term for molecules including interleukins, monokines and lymphokines. |
| Bursa of Fabricius | Specialised organ associated with the cloaca that is the primary site of B-cell development in birds. |
| Affinity | Strength of binding of one molecule to another; specifically the binding of a single antigenic epitope to a single Fab binding site within an immunoglobulin. |
| Avidity | Strength of overall binding of two molecules that contact at multiple sites; specifically the binding of multiple antigenic epitopes by multiple Fab binding sites within an immunoglobulin. |
| Anaphylotoxin | Substance capable of directly degranulating a mast cell; typically C3a and C5a of the complement pathway. |
| Antigen | Substance that initiates a specific immune response; technically a molecule that can bind to specific antibody, although some antigens do not elicit antibodies as part of the immune response. |
| T cells | T cells develop in bone marrow and mature in thymus. All T cells have CD3+. Antigen presentation stimulates T cell to become either cytotoxic CD8+ cells or helper CD4+ cells. |
| CD4 | T helper cells, some T reg cells |
| T regulatory cells | T lymphocyte that mediates suppression of T and B cell activity. Categorised as either natural or induced. CD4+, CD25+ |
| Th1/Th2 | Th1 and Th2 cells cross-regulate each other: Th1 cells are pro-inflammatory; Th2 cells are anti-inflammatory. |
| Innate immunity | That form of more primitive immunity that is evolutionarily older and provides continuous protection of body surfaces. Nonspecific defence mechanisms that come into play immediately or within hours of an antigen’s appearance in the body. Primitive defence systems include antibiotics (e.g. penicillins – soluble molecules released by bacteria and fungi), and phagocytosis (phagocytes e.g. neutrophils, macrophages, basophils – engulf organic material and whole cells). |
| Specificity | The probability that a diagnostic test will correctly identify those animals in a population that do not have the disease under consideration. |
| Thymus | Thymus selects cells that can distinguish self and foreign proteins. T cells mature in thymus (origin of term ‘T cell’). |
| Passive immunity | Transfer of collected antibody or serum to animal, clearing body of toxin by neutralisation e.g. antitoxins (tetanus, snakebite antivenin, rabies treatment), colostrum |
| Allograft | Transplant of tissue or organ between genetically dissimilar individuals of the same species. |
| Isograft | Transplant of tissue or organ between genetically identical individuals. |
| Xenograft | Transplant of tissue or organ from one species to another. |
| Autograft | Transplant of tissue or organ in a single individual but from different sites. |
| Cross-reactivity | Two antigens may share common or similar epitopes, enabling recognition by more than one antigen receptor (immunoglobulin or TCR). |
| TCR | Two-chain molecule (or chains) on the surface of a T lymphocyte that recognises antigenic peptide combined with Major Histocompatibility Complex on the surface of the APC. (T cell receptor) |
| Subunit (vaccine) | Vaccine containing an antigenic fragment of an organism rather than the entire organism itself. |
| Idiotope | Variable region of an antibody: location of the paratope (which binds to epitope) |
| Leukocyte | White blood cells = immune cells (no haemoglobin, i.e. not red blood cells) |
| Eosinophil | White cells that stain with eosin. 2-5% of granulocytes. Can be phagocytic but main function is exocytosis (release of tissue-destroying and anti-parasitic acidic granules) |
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