The Human Immune System

• Your immune system can attack pathogens. If pathogens do make it into your body, your immune system kicks in to destroy them.

  The most important part of your immune system is the white blood cells. They travel around in your blood and crawl into every part of you, constantly patrolling for pathogens.
• TYPES OF WHITE BLOOD CELLS

  • Lymphocytes 
  • Phagocytes
  • Neutrophils 
  • Basophils
  • Eosinophils
  • Monocytes
• When phagocytes enter the body, our bodies start to produce antibodies.

  • Every cell has molecules on its surface called antigens.
  • Each antigen is unique to the specific cell type that it's found on. White blood cells have special receptors in their membrane which help them to identify antigens on pathogens.

  In a healthy person, white blood cells recognise antigens on pathogens as non-self (foreign) and antigens on normal body cells as self.

  When they come across non-self antigens the immune system is triggered to destroy any invading pathogens
• Three main lines of attack of our immune system:

  1. Consuming them
  2. Producing antibodies
  3. Producing antitoxins
• Consuming Them Phagocytes 

  • Some white blood cells (phagocytes) have a flexible membrane and contain lots of enzymes.
  • Type of white blood cell that when it enters the body, our bodies start to produce antibodies.

  Phagocytosis - engulfs (ingest) foreign cells and digests them.

  Eosinophils - a type of white blood cell that releases enzymes that break down pathogens.

  Phago - eating

   Cyto - cell 
• Antibodies

  • These are produced rapidly and are carried around the body to lock on to all similar pathogens.
  • May disable the pathogen or 'tag' the pathogens, which helps the phagocytes find them so they can engulf them.

  Antibodies are specific - they will neutralise the microbe they have been made for. They do this by recognising the antigen on the surface of the microbe.
• Producing Antibodies

  1. The white blood cell “sees” the pathogen (microbe).
  2. The cell produces antibodies to "fit" the pathogen.
  3. The antibodies fit onto the pathogens and cause them to "clump".
  4. The pathogens are "eaten" by the white blood cells.
• When white blood cells come across a foreign antigen on a pathogen, receptors in the membrane bind to the antigen. The white blood cells then start to produce proteins called antibodies which

  lock onto the antigens on the invading cells.The antibodies produced are specific to that type of antigen —they won't lock on to any others.

  • B-lymphocytes - white blood cells that produce antibodies.
• The white blood cells that detect the pathogen then divide to produce more copies (clones) of the same white blood cell, so that more antibodies can be produced.

  Memory cells  - Some white blood cells stay around in the blood after the pathogen has been fought off..

  • If the person is infected with the same pathogen again, the memory cells will trigger the rapid production of the antibodies needed to destroy it, before the pathogen causes the disease.
• Producing Antitoxins

  Some pathogens can cause problems for the body by the toxins which they produce.

  Some white blood cells also produce antitoxins which counteract these toxins and so limit any damage done by the invading pathogens
• Macrophages

  • effector cells of the innate immune system that phagocytes bacteria, secrete both pro-inflammatory and antimicrobial mediators.
  • detects things that are foreign to the body, e.g. pathogens
• Receptors

  • surface markers