[Unit 5.3] | T-Lymphocytes & Cell-Mediated Immunity

Question 1

What is an antigen?

Answer 1

A part of an organism that is recognised as non-self by the immune system.

Question 2

What are the differences between B-lymphocytes and T-lymphocytes?

Answer 2

• B: Matured in bone marrow.
• T: Matured in thymus gland.

•B: Associated with humoral immunity (involving antibodies present in bodily fluids / humour).
• T: Associated with cell-mediated immunity (involving body cells).

Question 3

If T-lymphocytes cannot directly recognise foreign antigens, how do they respond to infections?

Answer 3

• They recognise non-self material via antigen-presenting cells:

• Phagocytes
• Body cells invaded by a virus
• Cancer cells

Question 4

Describe the process of cell-mediated immunity.

Answer 4

1. Pathogens are taken in by phagocytosis.
2. The phagocyte places antigens from the pathogen on its cell-surface membrane.
3. Receptors on a specific helper T cell complement these antigens.
4. The attachment activates the T cell to rapidly divide by mitosis.
5. The cloned cells:

• Become memory cells
• Stimulate phagocytes (increasing the rate of phagocytosis)
• Stimulate B cells to divide & secrete their antibodies
• Activate cytotoxic T cells

Question 5

How do cytotoxic T cells destroy pathogens?

Answer 5

• Produces perforin.

• Which creates holes in the membrane of a cell and therefore makes it freely permeable to all substances.

• Cell dies (often by bursting).