Immune System Definitions Virus an acellular infectious particle consisting of nucleic acid surrounded by a protein shell Immune System a system of cells and tissues that acts to defend the body against foreign cells and infectious agents Immunity the resistance to a given pathogen conferred by the activity of the immune system Pathogen Infectious agents including certain viruses bacteria fungi and parasites Many pathogens trigger an immune response Innate Immunity nonspecific defenses such as physical and chemical barriers and phagocytic cells that are present from birth and are always active Adaptive Immunity a prospective response mediated by lymphocytes that confers longlasting immunity against specific pathogens Lymphocyte a specialized white blood cell of the immune system Histamine a molecule released by damaging tissue and during allergic reactions Inflammatory Response an innate defense that is activated by local tissue damage Phagocyte a type of white blood cell that engulfs and ingests damaged cells and pathogens Macrophage a phagocytic cell that resides in tissues and plays an important role in the inflammatory response Neutrophil a phagocytic cell in the circulation that plays an important role in the inflammatory response Natural Killer Cell a type of white blood cell that acts during the innate immune response to find and destroy virally infected cells and tumor cells Interferon antiviral proteins produced by virally infected cells to help protect adjacent cells from becoming infected Complement Proteins proteins in blood that help destroy pathogens by coating or puncturing them B Cells white blood cells that mature in the bone marrow and produce antibodies during the adaptive immune response Thymus the organ in which T cells mature T Cells white blood cells that mature in the thymus and can destroy infected cells or stimulate B Cells to produce antibodies depending on the type of T cell Lymph Nodes small organs in the lymphatic system where B and T cells may encounter pathogens Lymphatic System the organ system that works with the immune system allowing B and T cells to respond to pathogens Humoral Immunity the type of adaptive immunity that fights infections and other foreign substances in the circulation and lymph fluid Helper T Cell a type of T cell that helps activate B cells during humoral responses Antigen a specific molecule or part of a molecule to which specific antibodies can bind and against which an adaptive response is mounted Plasma Cell an activated B cell that divides rapidly and secretes an abundance of antibodies Antibody a protein produced by Bcells that binds to antigens and either neutralizes them or flags other cells to destroy pathogens Cell Mediated Immunity the type of adaptive immunity that rids the body of altered that is infected or foreign cells Cytotoxic T Cell a type of T cell that destroys altered cells including virally infected cells Allergy a misdirected immune response against environmental substances such as dust pollen and foods that causes discomfort in the form of physical symptoms Autoimmune Disease a misdirected immune response in which the immune system mistakenly attacks healthy cells Primary Response the adaptive response mounted the first time a particular antigen is encountered by the immune system Memory Cell a long lived B or T cell that is produced during the primary response and that is rapidly activated in the secondary response Secondary Response the rapid and strong response mounted when a particular antigen is encountered by the immune system subsequent to the first encounter Vaccine a preparation of killed or weakened microorganisms or viruses that is given to people or animals to generate a memory immune response Antigenic Drift changes in viral antigens caused by genetic mutation during normal viral replication Antigenic Shift changes in antigens that occur when viruses exchange genetic material with other strains
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