4.1.7 T-Lymphocyte Response

Question 1

What is 3rd line of defence?

Answer 1

Lymphocytes and antibodies

Question 2

What are lymphocytes and what do they do?

Answer 2

• White blood cell
• Smaller than phagocytes
• Large nucleus
• Produced in bone marrow
• B lymphocytes (mature in bone marrow)
• T lymphocytes (mature in thymus gland)

Question 3

How do T lymphocytes mature?

Answer 3

• Gain specific T receptors on their cell surface
• Receptors complementary to different antigens
• Some T cells have the same T cell receptors, so they are clones of each other
• The clones differentiate into different types of T cells (T helper cells, T killer cells, T regulatory cells)
• Variation in T cell receptors allow T cells to recognise lots of antigens found on pathogens and their toxins
• T cells remain inactive til they counter specific antigen again

Question 4

How do T lymphocytes respond to infection?

Answer 4

• Antigens presented by macrophages on their cell surface membrane
• Bind with complementary T cell receptors on T cells specific to the pathogen
• Causing T cells to be activated
• Clonal expansion occurs via mitosis producing clones

T helper cells :
- Release chemical signalling molecules called interleukins (type of cytokine)
- Increase phagocytosis
- Activate B cells

T killer cells :
- Attach to foreign antigens on cell surface membrane of infected cells
- Secrete perforins, punching holes in the membrane of infected cells
- Toxic substances secreted killing the infected cell and the pathogen

T regulatory Cells :
- Prevent T cells from attacking and killing uninfected host cells
- Shut down immune system once body is cleared of pathogen

T memory Cells :
- Remain in blood, so if same pathogen encountered the process of clonal selection occurs far quicker