Module 4 definitions pk

• VIRUS: Acellular non-living particles which are smaller than bacteria, between 20-300nm. Consist of DNA or RNA enclosed within a protein coat called a capsid.
• PHAGOCYTOSIS: The upake of solid material into cells. Pseudopodia project from the cell, surround the solid material e.g. microbe, to encapsulate the material into a phagocytic vesicle/ vacuole. 'Cell eating'.
• PINOCYTOSIS: Method by which small particles and liquids are taken into cells. The plasma membrane invaginates to form very small vesicles. 'Cell drinking'.
• PSEUDOPODIA: Protrusions of the cell membrane which resemble 'false feet'. Formed during phagocytosis. Pseudopodia extend and surround large particles or microbes, to seal them into a vesicle.
• INVAGINATION: Folding in of the plasma membrane to form a pocket.
• PATHOGEN: A disease causing organism; many are microorganisms such as viruses, bacteria, fungi and protoctists.
• COMMUNICABLE DISEASE: Diseases caused by a pathogen which is transmitted from one host organism to another.
• NON-COMMUNICABLE DISEASE: Diseases not caused by pathogens and have numerous causes eg. Genetic; degenerative; deficiency and lifestyle.
• DISEASE TRANSMISSION: The transfer of a pathogen from an infected organism to an unifected organism.
• ANTIGEN: Any part of an organism or substance that is recognised as foreign/non-self by the immune system and stimulates an immune response. Antigens are often proteins on the cell surface membranes or cell walls of invading cells such as microorganisms or abnormal body cells.
• NATURAL PASSIVE IMMUNITY: This occurs when antibodies cross the placenta during pregnancy and when a young child is breast fed by its mother. No direct contact with the antigen is required to produce immunity. Antibodies are not replaced when they are broken down and no memory cells are formed so there is no lasting immunity.
• NATURAL ACTIVE IMMUNITY: Results from an individual becoming infected with a pathogen under normal natural circumstances. The body produces its own antibodies and may continue to do so for many years.
• ARTIFICIAL PASSIVE IMMUNITY: Occurs when antibodies are introduced into individuals from another source. No direct contact with the antigen is required to produce immunity. Antibodies are not replaced when they are broken down and no memory cells are formed so there is no lasting immunity. Examples include anti-venom given to victims of snake bites. People who are likely to have tetanus, diptheria or rabies are often given antitoxin antibodies by injection as a precaution.
• ARTIFICIAL ACTIVE IMMUNITY: This forms the basis of vaccination [immunisation]. The vaccine contains one or more antigens to stimulate an immune response.
• NEUTROPHIL: A short lived phagocytic cell produced in the bone marrow that circulates in the blood. They have lobed nuclei and granular cytoplasm.
• MONOCYTE: A larger cell than a neutrophil that circulates in the blood and leaves to remain as a long lived macrophage in tissues such as the lungs.
• MACROPHAGE: A large long lived phagocytic cell that remains in tissues. Macrophages process pathogens and present antigens to T lymphocytes.
• DENDRITIC CELL: A large phagocytic cell with lengthy extensions to give a large surface area to interact with pathogens and with lymphocytes.
• PHAGOSOME


  A phagocytic vesicle containing the engulfed pathogen.
• LYSOZYME: A type of enzyme present in lysosomes. Lysozymes hydrolyse the cell walls of ingested bacterial once lysosomes have fused with phagosomes during phagocytosis.
• B LYMPHOCYTE: Originate from stem cells in the bone marrow, where they differentiate and mature. B cells spread out through the body's lymphatic system and during an immune response, they become plasma cells.
• T LYMPHOCYTE: Type of white blood cell which originates in bone marrow but matures in the thymus gland. When T cells respond during an immune response, they do not make and release antibodies.
• HELPER T CELL: Type of T cell that coordinates an immune response by stimulating the responses of B cells and cytotoxic T cells by producing chemical signals such as interleukins.
• T KILLER CELL: Type of T cell that kills abnormal cells and body cells that are infected by pathogens, by producing a protein called perforin that makes holes in the cell surface membrane. The cell membrane becomes freely permeable to all substances.
• T REGULATOR CELL: Type of T cell that stops the immune responses and prevents T cells attacking the body's own cells and tissues.
• ANTIGEN PRESENTING CELL: Macrophages in the lymph nodes engulf pathogens by endocytosis and then 'cut up'. Antigens from the bacterial or virus surface are incorporated within proteins which then become part of the macrophage cell surface membrane.
• CELL MEDIATED IMMUNITY: T lymphocytes only respond to antigens that are presented on a body cell, rather than antigens within body fluids.
• HUMORAL IMMUNITY: B lymphocytes produce specific antibodies in response to specific antigens present on the surface of a pathogen, foreign cell, toxin, damaged or abnormal cell circulating in the blood and tissue fluid.
• ANTIBODY: A plasma protein known as an immunoglobulin. Synthesised by B cells. Y shaped molecule consisting of four polypeptide chains [two long heavy chains; two short light chains] with two specific identical binding sites in the variable region. Each binding site fits precisely onto a specific antigen.
• CLONE: A group of genetically identical cells. In the immune response, there are clones of B cells and clones of T cells. Each clone has its own unique cell surface receptor complementary to a specific antigen.
• CYTOKINES: Small protein molecules that act as cell signalling compounds. Many of them are involved in stimulating B cells to divide and develop into plasma cells and memory cells. Some T helper cells secrete cytokines that stimulate macrophages to carry out phagocytosis more aggressively. Interleukins are included in the cytokine group.
• INTERLEUKINS: A group of cytokines which regulate the immune and inflammatory responses. The majority of interleukins are produced by T helper cells [CD4], macrophages, monocytes and endothelial cells.
• MONOCLONAL ANTIBODY: A single type of antibody produced by a clone of plasma cells, which have originated from a specific B lymphocyte. Monoclonal antibodies have uses in medical diagnosis e.g. prostate cancer; pregnancy testing and therapeutic drug treatment for cancer.
• CLONAL SELECTION: The process during the immune responses when specific clones of B cells and/or T cells interact with antigens displayed on APC's.
• CLONAL EXPANSION: Small groups of identical B cells and T cells undergo cell division by mitosis to produce effector cells such as plasma cells and memory cells, during an immune response.
• PLASMA CELL: An activated B cell that makes and releases antibodies during the immune response.
• MEMORY CELL: Lymphocytes which develop during the primary immune response and retain the ability to antibodies quickly when an antigen enters the body on a second, or subsequent occasion.
• PRIMARY IMMUNE RESPONSE: The production of antibodies for the first time by plasma cells, following exposure to a foreign antigen.
• SECONDARY IMMUNE RESPONSE: The production of antibodies by memory cells, following a second or subsequent exposure to the original antigen. Response is quicker, more antibody molecules are produced and the response lasts for longer.
• VARIABLE REGION


  Antigen binding site on an antibody/immunoglobulin