7D: Third Line of Defence

Question 1

Third Line of Defence

Answer 1

a subset of the immune system within vertebrae’s that is composed of the humoral and cell-mediated responses which create a specific immune response and form immunological memory

- Known as the adaptive/specific immune system

Question 2

Characteristics of the Third Line of Defence

Answer 2

• Specificity: the adaptive immune system responds to each distinct pathogen in a unique and tailored manner
  - Immunological Memory: the adaptive immune system results in the production of cells that allow the body to respond to future re-infections by a previously encountered pathogen quickly and effectively.

Question 3

Antigen Presentation

Answer 3

involves the selection of a T helper cell

Question 4

T Lymphocyte

Answer 4

a lymphocyte that plays an important role in cell-mediated immunity.

- Differentiates into Cytotoxic T cells, T memory Cells and T helper cells

Question 5

T Helper Cell

Answer 5

helps selected B and T cells differentiate and undergo clonal expansion

- Each has a unique set of T cell receptors for a single antigen on its surface, facilitating the specificity of the adaptive immune response
- When this interaction occurs, the cell becomes 'selected' and helps to initiate the adaptive immune response either through the humoral or cell-mediated responses

Question 6

B Lymphocyte

Answer 6

a type of lymphocyte that plays an important role in humoral immunity and differentiates into plasma cells and B memory cells

- Their surface is covered in B cell receptors / antibodies
- Reside within lymph nodes
- Activated through interactions with pathogenic antigens and T helper cells

Question 7

B Lymphocyte Cells Differentiate into

Answer 7

• B Memory Cell: responsible for providing long lasting immunological memory of an antigen
• Plasma Cells: responsible for the generation and secretion of antibodies during the humoral response

Question 8

Humoral Immunity

Answer 8

an adaptive immune response in which extracellular pathogens are neutralised and destroyed by the secretion of specific antibodies produced by plasma cells

- Known as B cell immunity
- Primarily acts against extracellular pathogens

Question 9

Humoral Immune Response

Answer 9

1. • A pathogen with an antigen that is complementary in shape to the antigen binding site on the receptor of a B cell interacts with that B cell.
   • When this occurs, the B cell is said to have been selected
   2. • a T helper cell is then selected through antigen presentation which also has a complementary receptor to the antigen
      • The complementary receptor to the antigen will recognise the selected B cell and secrete a number of different cytokines and interleukins
      • These cytokines cause the B cell to undergo clonal expansion
   3. • The T helper cell also then stimulates the selected B cell via cytokines to undergo the process of differentiation
      • B cells are driven to differentiate into B memory cells and Plasma cells
   4. • After differentiating, plasma cells secrete antibodies into the blood in order to defend against the selected pathogen
        
        • B memory cells reside in the body for a prolonged period of time and are responsible for immunological memory

Question 10

Clonal Expansion

Answer 10

the process in which many copies of a lymphocyte are generated

Question 11

Clonal Selection

Answer 11

the process in which B and T cells encounter an antigen that matches their antigen binding site,

Question 12

Antibodies

Answer 12

Antibodies: proteins produced by plasma cells during the Adaptive Immune Response that is specific to an antigen and combats a pathogen by binding to the antigens on the pathogens surface

- Released by plasma cells and are proteins
- composed of 4 polypeptide chains(2 heavy and 2 light chains)
- Heavy chains are joined by a disulphide bond Each antibody is constructed with two regions; a constant and variable region

Question 13

Types of Antibodies

Answer 13

• IgA: found in mucus, breast milk and saliva
  
  • IgD: important or the activation of other immune cells
  • IgE: least common and protects against parasitic worms and responsible for allergic reactions
  • IgG: most common antibody which is able to cross the placenta and travel to the foetus
    IgM: the first type of antibody produced by plasma cells in response infections

Question 14

5 Key Functions of Antibodies

Answer 14

Neutralisation:
- Antibodies can block pathogens by blocking the site viruses use to enter the host cell

Agglutination:
- Antibodies bind with antigens from 2 different pathogens, forming an antigen-antibody complex making it easier for phagocytes to recognise and destroy pathogens

Immobilization:
- Antibodies can restrict the movement of pathogens around the body when forming large antigen-antibody complexes

Opsonisation:
- Antibodies can directly bind to the surface of pathogens, making it easier for phagocytosis to occur

Activation of Complement Proteins:
- Antibodies attach to the outside of pathogens, facilitating the formation of Membrane Attack Complexes

Question 15

Cell Mediated Immunity

Answer 15

involves the destruction of infected or abnormal cells via clonal selection of a cytotoxic T Cell

• Primarily acts against intracellular pathogens

Question 16

Cytotoxic T Cell

Answer 16

responsible for destroying infected or abnormal cells

• Looks for cells with MHC I markers displaying antigens that have been broken down on the cell surface signifying foreign viral antigens

Question 17

Key steps In Cell Mediated Immunity

Answer 17

1. • As T Helper Cells are selected, antigen presenting cells come upon a naive T Cell with a T receptor matching the antigen, initiating clonal selection
   • The naive T cell becomes selected and is stimulated by cytokines, from the T Helper Cell, to help undergo the process of clonal expansion and differentiation
   2. • The new clones differentiate into cytotoxic T cells and T memory Cells
   3. • The cytotoxic cells then arrive at the infection site and all have T cell receptors specific to the foreign antigen
      • Upon finding an abnormal cell presenting complementary foreign antigens on its MHC I , the cytotoxic T cell binds to the abnormal cell via interactions between the T cell receptor and the antigen MHC I complex
      • Chemicals such as perforin are secreted by the cytotoxic T cell to induce apoptosis

Question 18

Types of Long Lasting Immunological Memory

Answer 18

• B Memory Cells: rapidly divide and form new antibody-producing plasma cells when they encounter an antigen matching their receptor
  
  • Are also constantly secreting low amounts of antibodies meaning the person will always have a trace of antibodies in their blood

T Memory Cells: change rapidly into T helper cells and cytotoxic T cells upon stimulation by an antigen presenting cell that is presenting a previously encountered antigen

Question 19

Advantages of Immunological memory

Answer 19

• Creates more rapid and effective immune responses
• Helps prevent the formation of a disease in those re-exposed to a previously encountered pathogen, as it can no longer replicate fast enough