immunity

• Pathogen


  A microorganism that causes disease
• Self


  The body's own cells and molecules.
• Foreign (non-self)


  Not your own body's cells and molecules.
• Antigen


  A molecule that triggers an immune response by lymphocytes.
• Lymphocyte


  Type of white blood cell responsible for the immune response. They become activated in the presence of antigens. There are two types: B lymphocytes and T lymphocytes.
• Phagocyte


  Type of white blood cell which carries out a non-specific immune response and ingests and breaks down pathogens by phagocytosis.
• Phagocytosis


  Mechanism by which phagocytes engulf particles to form a vesicle or a vacuole.
• Lysosome


  Contain enzymes called lysozymes which they release into the phagosome which hydrolyse the bacterium.
• Phagosome


  A vesicle formed as the bacterium is engulfed by the phagocyte. The lysosome release their lysozymes into the phagosome.
• Antigen-presentation


  When an antigen-presenting cell e.g. phagocyte displays foreign antigens on their own cell-surface membrane.
• Cell-mediated immunity


  The type of response when T lymphocytes respond to antigens that are presented on a body cell.
• T Cells


  Cells which mature in the thymus and are associated with cell-mediated immunity.
• Clonal Selection


  As the receptor on a helper T cell attaches to the antigen this activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells. These cloned T cells stimulate B cells to divide and form a clone of identical B cells all of which produce the antibody that is specific to the foreign antigen.
• TH cells (helper T cell)

  Contain receptors which respond to a single antigen. Many different types of T cell, each one responds to a different antigen.
• TC cells (cytotoxic T cells)


  Kill abnormal cells and body cells that are infected by pathogens by producing a protein called perforin which makes holes in the cell-surface membrane.
• Humoral Immunity


  The type of response which involves B lymphocytes and antibodies.
• B Cells


  Each type of B cell produces a specific antibody that responds to one specific antigen.
• Plasma B Cells


  When the B cell is activated to divide by mitosis it gives a clone of plasma cells which produce and secrete the specific antibody that exactly fits the antigen on the pathogen's surface.
• Antibody


  A protein with specific binding sites produced by B cells in response to the presence of appropriate antigen.
• Memory B Cells


  Some B cells develop into memory cells which can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies as part of the secondary response.
• Monoclonal antibodies


  Antibodies produced by a single clone of cells.
• Primary Response


  Caused by initial response to the antigen which involves the production of antibodies and memory cells.
• Secondary response


  Caused by second exposure to the antigen. Memory cells are responsible for this response - they divide rapidly and develop into plasma cells (which secrete many antibodies quickly) and more memory cells.
• Passive immunity


  Resistance to disease that is acquired from the introduction of antibodies from another individual, rather than an individual's own immune system e.g. across the placenta or in the mother's milk. It is usually short lived.
• Active immunity


  Resistance to disease resulting from the activities of an individual's own immune system whereby an antigen induces plasma cells to produce antibodies.
• Natural immunity


  A type of active immunity resulting from an individual becoming infected with a disease under normal circumstances.
• Artificial immunity


  A type of active immunity resulting from vaccination. It involves inducing an immune response in an individual without them suffering symptoms of the disease.
• Vaccination


  The introduction of a vaccine containing appropriate disease antigens into the body, by injection or mouth, in order to induce artificial immunity.
• Herd immunity


  Arises when a sufficiently large proportion of the population has been vaccinated which makes it difficult for a pathogen to spread within that population.
• Antigenic variability


  Pathogen may mutate frequently so that its antigens change suddenly rather than gradually which means vaccines become ineffective because the new antigens on the pathogen are no longer recognized by the immune system.
• HIV


  Human immunodeficiency virus which causes the disease acquired immune deficiency syndrome (AIDS). It has a lipid envelope, attachment proteins, a capsid and two single strands or RNA and enzymes.
• Reverse transcriptase


  An enzyme in HIV which enables the production of DNA from RNA.
• Retrovirus


  A group of viruses which have the ability to make DNA from RNA because they have reverse transcriptase.
• mRNA


  A single stranded polynucleotide found in HIV.
• AIDS


  The disease caused by HIV.
• ELISA test

  Enzyme linked immunosorbent assay which uses antibodies to detect the presence and quantity of a protein in a sample.
• Antibiotic


  A substance produced by living organisms that can destroy or inhibit the growth of microorganisms