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| An animal body's system of defenses against agents that cause disease. |
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| A form of defense common to all animals that is active immediately upon exposure to pathogens and that is the same whether or not the pathogen has been encountered previously. |
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| A vertebrate-specific defense that is mediated by B lymphoctyes (B-cells) and T lymphocytes (T-cells). It exhibits specificity, memory, and self-nonself recognition. Also called acquired immunity. |
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| An enzyme that destroys bacterial cell walls; in mammals, found in sweat, tears, and saliva. |
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| A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells in animals (in mammals, mainly macrophages, neutrophils, and dendritic cells). |
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| A membrane receptor on a phagocytic white blood cell that recognizes fragments of molecules common to a set of pathogens. |
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| The most abundant type of white blood cell. Neutrophils are phagocytic and tend to self-destruct as they destroy foreign invaders, limiting their life span to a few days. |
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| A phagocytic cell present in many tissues that functions in innate immunity by destroying microbes and inacquired immunity as an antigen-presenting cell. |
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| An antigen-presenting cell, located mainly in lymphatic tissues and skin, that is particularly efficient in presenting antigens to helper T cells, thereby initiating a primary immune response. |
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| A type of white blood cell that can kill tumor cells and virus-infected cells as a part of innate immunity. |
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| A protein that has antiviral or immune regulatory functions. Interferon-alpha and interferon-beta, secreted by virus-infected cells, help nearby cells resist viral infection; interferon-gamma, secreted by T cells, helps activate microphages. |
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| A group of about 30 blood proteins that may amplify the inflammatory response, enhance phagocytosis, or directly lyse extracellular pathogens. |
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| An innate immune defense triggered by physical injury or infection of tissues involving the release of substances that promote swelling, enhance the infiltration of white blood cells and aid in tissue repair and destruction of invading pathogens. |
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| A substance released by mast cells that causes blood vessels to dilate and become more permeable in inflammatory and allergic responses, |
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| A vertebrate body cell that produces histamine and other molecules that trigger inflammation in response to infection and in allergic reactions. |
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| Any of a group of small proteins secreted by a number of cell types, including macrophages and helper T cells, that regulate the function of other cells. |
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| A type of white blood cell that mediates immune responses. The two main classes are B cells and T cells. |
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| A small organ in the thoracic cavity of vertebrates where maturation of T cells is completed. |
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| The class of lymphocytes that mature in the thymus; they include both effector cells for the cell-mediated immune response and helper cells required for both branches of adaptive immunity. |
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| The lymphocytes that complete their development in the bone marrow and become effector cells for the humoral immune response. |
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| A substance that elicits an immune reponse by binding to receptors of B cells, antibodies, or of T cells. |
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| The general term for a surface protein, located on B cells and T cells, that binds to antigens, initiating adaptive immune responses. The antigen receptors on B cells are called B cell receptors, and the antigen receptors on T cells are called T cell receptors. |
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| A small, accessible region of an antigen to which an antigen receptor or antibody binds; also called an antigenic determinant. |
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| One of the two types of polypeptide chains that make up an antibody molecule and B cell receptor; consists of a variable region, which contributes to the antigen-binding site, and a constant region. |
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| One of the two types of polypeptide chains that make up an antibody molecule and B cell receptor; consists of a variable region, which contributes to the antigen-binding site, and a constant region. |
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| A protein secreted by plasma cells (differentiated B cells) that binds to a particular antigen; also called immunoglobin. All antibodies have the same Y-shaped structure and in their monomer form consist of two identical heavy chains and two identical light chains. |
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| Any of the class of proteins that function as antibodies. Immunoglobulins are divided into five major classes that differ in their distribution in the body and antigen disposal activities. |
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| MHC (major histocompatabiliy complex) molecule |
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| A host protein that functions in antigen presentation. Foreign MHC molecules on transplanted tissue can trigger T cell responses that may lead to rejection of the transplant. |
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| The process by which an MHC molecule binds to a fragment of an intracellular protein antigen and carries it to the cell surface, where it is displayed and can be recognized by a T cell. |
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