adaptive immunity - unit 4 AOS 1

Question 1

adaptive immunity/third line of defence

Answer 1

• The third line of defence (adaptive immune response) involves a specific response against a specific pathogen, with memory retained for future infection. This response is usually only required if an infection is not cleared by the innate response.

Question 2

initiation of the immune response

Answer 2

• antigen presentation
• a pathogen is engulfed via phagocytosis by either a macrophage or a dendritic cell
• parts of the pathogen get presented on the phagocytes MHC II markers.
• the antigen presenting cells travels to a lymph node where it will interact with T helper cells that carry receptors for that antigen.
• helper T cells then release cytokines which stimulate selected B and T cells to undergo clonal expansion and differentiation.

Question 3

B lymphocytes

Answer 3

• mature in bone marrow
• important for the humoral immune response
• differentiate into plasma cells and B memory cells
• plasma cells release antibodies against extracellular antigens
• B memory cells provide long- lasting immunity by retaining memory of antigens.

Question 4

T lymphocytes

Answer 4

• mature in the thymus and them migrate to lymph nodes
• important for the cell mediated immune response
• differentiates into cytotoxic T cells and T memory cells
• cytotoxic T cells eliminate infected and abnormal cells
• T memory cells provide long lasting immunity by retaining memory of antigens

Question 5

humoral immune response

Answer 5

• Humoral immunity involves the neutralisation and destruction of extracellular pathogens via the production and secretion of antibodies. It is also called the antibody mediated response

Question 6

steps of the humeral immune response

Answer 6

• Clonal selection occurs when an antigen presenting cell interacts with a B cell that is complementary.
• at the same time, antigen presenting cells interact with helper T cells which release cytokines that stimulate selected B cells to undergo clonal expansion and differentiation.
• B cells differentiate into plasma cells and B memory cells
• plasma cells secrete antibodies to destroy pathogens

Question 7

cell mediated immune response

Answer 7

• Cell-mediated immunity involves the destruction of infected or abnormal cells via the clonal selection of a cytotoxic T cell.

Question 8

steps in the cell mediated immune response

Answer 8

• Clonal selection occurs when an antigen presenting cell interacts with a naive T cell that is complementary.
• at the same time, antigen presenting cells interact with helper T cells which release cytokines that stimulate selected T cells to undergo clonal expansion and differentiation.
• T cells differentiate into cytotoxic T cells and T memory cells
• cytotoxic T cells asses MHC I markers for complementary foreign antigens an then releases chemicals which cause the cell to die via apoptosis.

Question 9

immunological memory

Answer 9

• B memory cells and T memory cells formed during the adaptive immune response remain in the blood for an extended period of time, allowing the body to respond to pathogens it has previously encountered quickly and effectively.
• B memory cells contribute to immunological memory by rapidly dividing and forming new antibody-producing plasma cells when they encounter an antigen that matches their receptor. they also release small amounts of their antibodies so these are constantly in the body.
• T memory cells proliferate rapidly into T helper cells and cytotoxic T cells upon stimulation by an antigen-presenting cell that is presenting a previously encountered antigen.

Question 10

antibodies

Answer 10

• Antibodies released by plasma cells are proteins with a quaternary structure anf they are specific to an antigen.
• They are composed of four polypeptide chains, including two heavy chains and two light chains, arranged into a ‘Y’ shape
• The two heavy chains are joined by a disulphide bond.
• The amino acid sequence varies greatly in the variable regions, located at the end of each arm of the Y-shaped molecule. These regions are called the antigen binding sites, where the antibody binds to its specific antigen.

Question 11

functions of antibodies

Answer 11

• Neutralisation of pathogens — antibodies bind to surface antigens on pathogens and form a coating that neutralises pathogens by blocking their receptors so that the pathogens cannot attach to healthy body cells and infect them.
• Opsonisation — antibodies bind to the surface antigens on pathogens to form antigen–antibody complexes and tag the pathogen for destruction. This activates phagocytes and complement proteins, leading to the destruction of the pathogen.
• antibodies bind to the surface antigens on pathogens to form antigen–antibody complexes. By doing this to various pathogens, it can cause them to clump together and be more visible to the immune system.
• Inflammation — antibodies can trigger the release of histamine, causing inflammation. They also activate a complement cascade.