• White blood cells are part of the body’s?immune system
• These specialised cells defend against pathogenic microorganisms
• There are two main types of white blood cell:
  • Phagocytes
  • Lymphocytes

   

Phagocytes

• Phagocytes carry out?phagocytosis?by?engulfing and digesting pathogens
  • Phagocytes have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells
  • Once they encounter the pathogenic cell, they will engulf it and?release digestive enzymes?to digest it
  • This is a?non-specific?immune response

   

• Phagocytes can be easily recognised under the microscope by their?multi-lobed nucleus?and their?granular cytoplasm

The process of phagocytosis

Lymphocytes

• Lymphocytes can easily be recognised under the microscope by their?large round nucleus?which takes up nearly the whole cell and their?clear, non-granular cytoplasm
• Lymphocytes?produce?antibodies
  • Antibodies are Y-shaped proteins with a shape that is?specific?(complementary) to the?antigens?on the surface of the pathogen
  • This is a?specific?type of immune response as the antibodies produced will only fit one type of antigen on a pathogen

   

The lymphocytes produce antibodies that are specific to the antigen on the pathogen

• Antibodies attach to the antigens and cause?agglutination?(clumping together)
• This means the pathogenic cells cannot move very easily
• At the same time,?chemicals?are released that signal to?phagocytes?that there are cells present that need to be destroyed

Agglutinated pathogens cannot move easily

• Lymphocytes?also produce?antitoxins?to neutralise toxins released by pathogens

Lymphocytes produce specific antitoxins to specific pathogens

• The body's?immune system?is highly complex, with white blood cells being the main component
• Once a pathogen has entered the body the role of the immune system is to prevent the infectious organism from reproducing and to destroy it
• An organism has immunity when they have?sufficient levels of antibodies?to protect it from a particular disease
  • As a result, they do not suffer from the disease or its symptoms

   

Response to infection

• The stages of infection and the subsequent immune response are as follows: 

   

  1. The pathogen enters the blood stream and?multiplies
  2. A release of?toxins?(in the case of bacteria) and?infection of body cells?causes?symptoms?in the patient
  3. Phagocytes?that encounter the pathogen recognise that it is an invading pathogen and?engulf and digest?(non-specific response)
  4. Eventually, the pathogen encounters a?lymphocyte?which recognises its?antigens
  5. The lymphocyte starts to produce?specific antibodies?to combat that particular pathogen
  6. The lymphocyte also?clones itself?to produce lots of lymphocytes (all producing the specific?antibody?required)
  7. Antibodies cause?agglutination?of pathogens
  8. Phagocytes?engulf and digest the agglutinated pathogens
  9. After the patient has recovered, they?retain antibodies?specific to the disease as well as?memory cells?(lymphocytes that recognise the pathogen)
  10. If the patient encounters the same pathogen again, it will trigger a secondary immune response
  11. Memory cells can produce much?larger quantities?of the required antibody in a much?shorter time?to fight off the pathogen before the patient suffers any symptoms