immunity

• capsule (prokaryotic cell)


  function of capsule is to protect the bacterial cell against the immune system of the host .

  IMPORTANT TO NOTE: capsule found on the very outside of the cell whereas cell wall SEPARATES capsule from the cell membrane
• Describe the first three steps of phagocytosis.


  When a pathogen invades the body, the pathogen releases chemicals such as toxins that attract phagocytes towards it down a concentration gradient. When the phagocyte reaches the pathogen, it binds to the pathogen via complementary receptors. The phagocyte then engulfs the pathogen encasing it in a vesicle. This structure is called a phagosome.
• What do pathogens release to attract phagocytes?

  Chemicals such as toxins
• How do phagocytes move towards pathogens?

  Down a concentration gradient
• What happens when a phagocyte reaches a pathogen?

  It binds to the pathogen via complementary receptors
• What structure is formed when a phagocyte engulfs a pathogen?

  A phagosome
• What do lysosomes do when they move towards the phagosome?

  They fuse with the phagosome
• What do lysosomes release into the phagosome?

  Lysozymes
• How do lysozymes break down the pathogen?

  Through hydrolysis reactions
• What happens to the soluble products from the breakdown of the pathogen?

  They are absorbed by the cytoplasm
• What happens to the remaining parts of the pathogen after digestion?

  They are expelled from the phagocyte
• explain how a pathogen can be destroyed by phagocytosis


  1. The phagocyte is attracted to chemicals released by the pathogen and moves down a concentration gradient.
  2. Receptors on the phagocyte bind to the pathogen.
  3. The phagocyte engulfs the pathogen to form a phagosome.
  4. Lysosomes in the phagocyte fuse with the phagosome.
  5. The lysosomes release lysozymes which hydrolyse the pathogen.
  6. The cytoplasm absorbs the soluble products of this reaction.
• Explain how the immune system carries out a nonspecific response against a pathogen.


  Phagocytes are involved in the nonspecific response against pathogens.The phagocyte is attracted to chemicals released by the pathogen and moves along a concentration gradient. Receptors on the phagocyte bind to the pathogen. The phagocyte engulfs the pathogen to form a phagosome. Lysosomes in the phagocyte fuse with the phagosome. The lysosomes release lysozymes which hydrolyse the pathogen. The cytoplasm absorbs the soluble products of this reaction.

  Explanation
• monoclonal antibodies


  antibodies with the same tertiary structure produced from cloned B cells
• Describe the sequence of events that produce plasma and memory B cells from a naive B cell.


  The naive B cell’s receptors bind to a complementary antigen on a pathogen. The B cell internalises the pathogen, processes the pathogen’s antigens and presents them on its surface.The processed antigens bind to complementary receptors on a helper T cell. Once stimulated, the helper T cell releases chemicals that cause the B cell to clone itself.Finally, the cloned B cells differentiate into plasma cells and memory B cells.
• What is the first stage of the humoral immune response?

  The primary response
• What happens when a naive B cell's receptors bind to complementary antigens on a pathogen?

  The B cell internalizes the pathogen, processes its antigens, and presents them on its surface
• How do processed antigens interact with helper T cells during the primary response?

  The processed antigens bind to complementary receptors on helper T cells
• What is the role of helper T cells in the primary immune response?

  They stimulate the B cell to clone itself
• What do cloned B cells differentiate into during the primary response?

  Plasma cells and memory B cells
• What is the function of plasma cells in the humoral immune response?

  They secrete antibodies
• What is the role of memory B cells after the pathogen is gone?

  They remain in the body for future encounters with the same antigen
• What occurs if the body re-encounters the same antigen?

  Memory B cells clone themselves and differentiate into plasma cells and memory B cells
• What is the term for the immune response that occurs upon re-encountering the same antigen?

  The secondary response
• What are the key steps in the primary stage of the humoral immune response?

  1. Naive B cell binds to complementary antigens.
  2. B cell internalizes and processes the pathogen.
  3. Antigens are presented on the B cell surface.
  4. Processed antigens bind to helper T cells.
  5. Helper T cells stimulate B cell cloning.
  6. Cloned B cells differentiate into plasma and memory B cells.
• What are the key steps in the secondary stage of the humoral immune response?

  1. Memory B cells recognize the same antigen.
  2. Memory B cells clone themselves.
  3. Cloned memory B cells differentiate into plasma cells and memory B cells.
• Describe the cell-mediated immune response.


  First, a naive helper T cell’s receptor binds to an antigen on an antigen-presenting cell. This stimulates the helper T cell to clone itself.The cloned helper T cells stimulate BB cells to clone, phagocytes to undergo phagocytosis, and cytotoxic T cells to target virus-infected body cells.When cytotoxic T cell receptors bind to antigens on virus-infected body cells, they release perforin. This protein creates holes in the cell surface membrane leading to cell death.
• Describe how antibodies lead to the destruction of a pathogen


  Antibodies bind to complementary antigens on the surface of the pathogen, forming antibody-antigen complexes.This causes pathogens to clump together in a process called agglutination, which makes it easier for phagocytes to engulf and destroy pathogens.
• HIV replication


  • Viral RNA enters the cell
  • Viral reverse transcriptase enzymes produce a DNA copy of the viral RNA
  • The DNA copy is inserted into the chromosomes of the cell
  • Each time the cell divides it copies the viral DNA
  • The infected cells remain normal as the viral DNA is inactive
• What occurs to the viral DNA after a person becomes HIV positive?

  It becomes active within the host cells.
• How does HIV affect helper T cells?

  It takes control of the helper T cell.
• What is the consequence of HIV taking control of helper T cells?

  More HIV particles are produced.
• What happens to helper T cells as a result of HIV infection?

  The helper T cell dies.
• What is released when helper T cells die due to HIV?

  Thousands of new HIV particles are released.
• What can the new HIV particles do after being released?

  They can infect other helper T cells.
• How does HIV affect the number of helper T cells in the immune system?

  It gradually reduces their number.
• What happens to B cells as a result of HIV infection?

  B cells are no longer activated.
• What is the consequence of B cells not being activated?

  No antibodies are produced.
• How does the decrease in antibodies affect the body?

  It decreases the body's ability to fight infections.
• What condition can result from the progression of HIV infection?

  AIDS (Acquired immune deficiency syndrome).