Adaptive Immune System

Question 1

What is an antigen?

Answer 1

Any molecule that can trigger an adaptive immune response aganist itself or the cell that it is bearing (or immunogen)

Question 2

Describe the basic adaptive immune response in 3 stages

Answer 2

1. Encounter and recognition of antigen by lymphocyte
   - antigen binds to receptors on lymphocyte (each antigen is specific for one type of antigen)
2. Lymphocyte activation
   - upon binding the lymphocyte becomes activated and undergoes several rounds of cell division, this is called clonal expansion
   - after activation some function as effector lymphocytes some are set aside as memory cells
3. The attack
   - Activated B cells differentiate into plasma cells that secrete antibodies into the blood
   - These antibodies opsonize pathogens or foreign substances and target them for attack by innate immune cells
   - Activated cytotoxic T cells directly attack and kill the antigen bearing cells
   - After the attack the majority of B cells, plasma cells and T cells die by apoptosis
   - Memory cells persist after immune response is complete

Question 3

What are primary lymphoid organs

Answer 3

The bone marrow and the thymus, this are the sites of initial sites of lymphocyte development. They supply the body with mature but naive lymphocytes (not yet activated)

Question 4

What are secondary lymphoid organs

Answer 4

Lymph nodes, spleen, tonsils and lymphocyte accumulations in linings of intestinal, respiratory, genital and urinary tracts.
This is where naive lymphocytes are activated to partcipate in adaptive immune response
(once in a secondary lymphoidal organs a mature lymphocyte from the primary organs can undergo cell division to produce identical lymphocytes, these are lymphocyte clones)

Question 5

What is the thymus?

Answer 5

• Lies in upper part of the chest
• relatively large at birth, grows till puberty
• gradually atrophies and is replaced by fatty tissue
• before atrophy the thymus contains mainly immature lymphocytes that develop into mature lymphocytes and migrate via blood to the secondary lyphpoidal organs

Question 6

What is the spleen?

Answer 6

• largest secondary lyphpoidal organs
• left part of abdominal cavity between stomach and diaphragm
• large collections of lymphocytes, macrophages and dendritic cells
• also phagocytoses ageing or dead erythrocytes

Question 7

Name 3 types of T cell

Answer 7

• Cytotoxic T cells CD8 - attack cells
• Helper T cells CD4 - activate B cells, macrophages and cytotoxic T cells
• Regulatory T cells (inhibits function of B cells and cytotoxic cells)