Specific Immune Response

Question 1

Specific Immune Response

Answer 1

Antigens: (glyco)proteins in the plasma membrane of a pathogen that stimulate the immune response.

Receptors on B/T plasma membranes are transmembrane glycoproteins that have specific external shape.

Question 2

T lymphocytes:

Answer 2

T lymphocytes: Surface covered with T cell receptors (involved in cell mediated immunity).
T helper cells – release cytokines (chemical messengers e.g. interleukins) that activate B cells, T killer cells and stimulate phagocytosis.
T killer cells – Attack and kill body cells that display the foreign antigen (i.e. infected by pathogen).
T memory cells – provide long-term immunity, remember specific antigen and will recognise it.
T regulator cells – inhibit or end the immune response after pathogen has been successfully removed. They are involved in preventing autoimmunity.

Question 3

B lymphocytes:

Answer 3

B lymphocytes: B cell receptors on cell surface membrane (humoral immunity).
Plasma cells – circulate in the blood, manufacturing and releasing antibodies.
B memory cells – immunological memory, remember specific antibodies needed to bind to antigen.

T & B lymphocytes made in bone marrow, T move to and mature in thymus gland, B mature in bone marrow

Question 4

Cell signalling:

Answer 4

Cells need to communicate to coordinate specific immune response. Chemicals called cytokines are released, they bind to complementary receptors on target B/T cell plasma membranes.
Examples of cytokines:
- Monokines released by macrophages, which attract neutrophils (by chemotaxis – movement of cells towards a chemical).
- T helper cells and macrophages release interleukins, which stimulate clonal expansion and differentiation of B and T cells.
- Many cells release interferon, which inhibits virus replication and stimulates T killer cell activity. Monokines, interleukins, and interferon are types of cytokine.

Cell-mediated immunity to the response to cells form the body that have been changed by pathogens by antigen processing. Humoral immunity is the response to foreign antigens leading to antibody production.

Question 5

Specific immune response

Answer 5

1. Macrophages engulf pathogens:
2. Clonal selection of T lymphocytes:
3. Clonal selection of B lymphocytes:
4. Plasma cells produce more antibodies:

Question 6

1. Macrophages engulf pathogens:

Answer 6

• Macrophage recognises foreign antigens of the pathogen and binds them (may be aided by
  opsonins).
• The pathogen is engulfed by endocytosis forming a phagosome.
• Lysosomes fuse to the phagosome and release hydrolytic enzymes into it that digest pathogen.
• The harmless products are absorbed into the cell.
• The macrophage does not fully digest pathogen, it moves the antigens to its cell surface membrane
  and exposes them – antigen presentation, forming an antigen-presenting cell (APC), so B/T lymphocytes recognise the foreign antigen – initiating the specific immune response.
• Role: to increase likelihood that antigen will come into contact with B/T cells.
• Macrophages also release monokines (cytokines), which attract neutrophils to infected area.
• Neutrophils are phagocytes that fully digest pathogens, they die after digesting a few.

Question 7

2. Clonal selection of T lymphocytes:

Answer 7

• T lymphocytes recognise foreign antigens on APCs (or pathogens that have entered lymph nodes),
  the specific complementary receptors on their surface membrane binds to the foreign antigen, activating the T lymphocyte – clonal selection.
• Each T lymphocyte has a specific receptor complementary to 1 specific foreign antigen.
• Clonal expansion – the T lymphocyte divides by mitosis to produce clones of itself.
• Differentiation – clones differentiate into T helper cells, T memory cells or T killers cells.
• T helper cells (and macrophages) produce interleukins (cytokines) which activate B lymphocytes –
  clonal selection, stimulate clonal expansion of B cells, and stimulate phagocytosis.
• Also release interferon, which inhibits virus replication and stimulates T killer cell activity.

Question 8

3. Clonal selection of B lymphocytes:

Answer 8

• B lymphocytes each have different receptors on their plasma membrane, that are complementary to
  a specific foreign antigen.
• The receptors on B lymphocytes also bind to the foreign antigens on APCs. Also T helper cells release
  interleukins that bind to receptors on B lymphocytes. These 2, activate B lymphocytes – clonal
  selection.
• Clonal expansion & differentiation – activated B lymphocytes divide by mitosis to form genetically
  identical plasma cells – that all produce same antibody) some don’t differentiate & become B memory cells.

Question 9

4. Plasma cells produce more antibodies:

Answer 9

• Plasma cells produce and secrete large numbers of the specific antibody that is complementary to
  the foreign antigens.
• Antibodies bind to the antigens on the pathogen rendering them harmless and aiding phagocytosis
  (opsonins/agglutinins) or neutralising toxins.
• B/T memory cells provide long-term immunity (protection) from the disease as they remain in the
  blood (not permanent, immunity lost if the person is no longer exposed to antigens).