3.2.4 Cell rec & immune system

• Viruses, bacteria, fungi, and protists are four types of pathogens.
• Pathogens cause disease by damaging cells or releasing toxins.
• Lymphocytes build up in numbers in order to be effective at destroying the pathogen, a process known as clonal expansion.
• Non-specific barriers of the immune system include stomach acid, skin, and ciliated epithelial cells in the trachea/bronchi.
• White blood cells cause destruction of pathogens by making antibodies, making antitoxins, and ingesting and digesting pathogens through a process called phagocytosis.
• Memory cells remain in the blood following a vaccine.
• An antibiotic is a medicine that kills bacteria, used to treat bacterial infections only.
• Malaria is caused by a protist.
• HIV is spread through bodily fluids or sexual contact (STI).
• Non-specific immune response is immediate, includes phagocytes, but does not involve memory cells and provides short-term immunity.
• Specific immune response is slower, includes lymphocytes, is specific for each pathogen, and provides long-term immunity.
• Pathogens have proteins, called antigens, on their cell-surface membranes that cause an immune response.
• The immune system operates in both a non-specific (immediate response) and specific (slower response) manner.
• Physical barriers and chemical barriers are part of the non-specific immune system.
• Phagocytosis, a process where phagocytes engulf and digest pathogens, is a part of the non-specific immune system.
• Cell-mediated Response, a type of immune response that involves T lymphocytes, is a part of the specific immune system.
• Humoral Response, a type of immune response that involves B lymphocytes, is a part of the specific immune system.
• The specific immune system has a lag time due to the formation of memory cells, but its response is specific depending on the pathogen encountered.
• The non-specific immune system does not form memory cells and its response is the same no matter which pathogen is encountered.
• antigens allow the immune system to identify pathogens, cells from other organisms of the same species, abnormal (cancerous) body cells and toxins.
• what are key differences between the non-specific and specific immune system?

  • non-specific immune system has the same response no matter the pathogen, while specific immune system has a response specific to pathogen
  • non-specific immune system is faster, while specific is slower/has a lag time because it is antigen dependent
  • non-specific immune system doesn’t give long lasting immunity while specific does as memory cells are formed.
• examples of physical barriers in the non-specific immune system?

  Skin, mucous membranes, ciliated membranes
• examples of chemical barriers in the non-specific immune system?

  stomach acid, enzymes in tears, skin secretions
• 3 types of identifying molecules (antigens) on pathogens?

  proteins, glycoproteins, glycolipids
• how are phagocytes specialised?

  Contain lysosomes (that contain hydrolytic enzymes)

  Lobed nucleus allows the cell to be flexible and move freely around pathogens
• Immunity is the ability of organisms to resist infection, by protecting against disease causing pathogens and toxins.
• T lymphocytes only respond to antigens on the body’s own cells (self-cells).These could be infected cells, cells from other organisms/species, or cancerous cells.
• The cell-mediated response is most effective against viruses as viruses use body cells to replicate. 
• What type of cells can T-lymphocytes recognise?

  Antigen-presenting cells

  Infected cells

  Transplanted cells

  Cancerous/abnormal cells
• Cytotoxic T Cells kill infected/abnormal cells by producing a protein called perforin that makes holes in the cell-surface membrane.  This makes it freely permeable and so it dies.
• T Helper cells are involved in cell recognition and stimulate other immune responses.
• B lymphocytes produce antibodies which are soluble in bodily fluids 
• B lymphocytes are produced from stem cells in the bone marrow and mature here too.
• Some B lymphocytes will differentiate into plasma cells. These are the “antibody-factories”.
• both plasma cells and memory B cells have receptors, which are membrane-bound antibodies.
• The variable region of an antibody has tertiary structure. Antigen-antibody complexes are formed here. 
• antibody structure?

  Complex quaternary proteins

  4 polypeptide chains - 2 long and heavy chains & 2 light and short chains

  Constant region is same in all, variable regions changes from antibody to antibody to be specific to antigens. 

  Antigen binding site is where antigen-antibody complexes are formed.

  Disulfide bonds hold the light and heavy chains together 
• 1. Invading pathogen has an antigen that is complementary to a receptor on B cell.
  2. The pathogen enters the B cell by endocytosis the B cell presents an antigen on its cell-surface membrane.
  3. A activated T helper cell binds to presented antigen.
  4. This stimulates the B cell to divide by mitosis (clonal selection)
  5. In each clone of B cells, the cells develop into one of two types of cell: plasma cell or memory B cell
  6. Antibodies attach to antigens on the pathogen which leads to destruction. The antibodies act as markers for phagocytes; clump multiple pathogens together, which is called agglutination.
• Describe the purpose of the humoral response.

  Create antibodies which destroy pathogens and create memory cells for long-lasting immunity 
• Explain why a T-cell cannot recognise a pathogen, but a B-cell can.

  B-cells can bind to antigens directly but T-cells can’t. T-cells have a receptor that must bind to a receptor on a self cell when recognising an antigen. Pathogens do not have this.