5.3 T lymphocytes and cell-mediated immunity

Question 1

What are antigens?

Answer 1

any part of an organism or substance recognized as non-self by the immune system and stimulate an immune response.

• usually proteins
• part of cell surface membrane/ cell wall
• triggers production of antibodies.

Question 2

What is cell-mediated immunity?

Answer 2

• immunity involving body cells
• respond to an organisms own cells which have been affected by non-self materials (anything with different antigens to self cells)

Question 3

What are antigen presenting cells?

Answer 3

cells which display foreign antigens on their surface.

• phagocytes do this after engulfing and hydrolyzing a pathogen.
• body cells invaded by viruses can present viral antigens

Question 4

How do T-lymphocytes respond to antigens?

Answer 4

• they only respond to antigens presented on a body cell
• The receptors on each T cell correspond to a single antigen, and there are a large number of different T cells, each one responding to a different antigen.

Question 5

How to T lymphocytes respond to a pathogen?

Answer 5

1) Pathogens invade body cells/ are taken in by phagocytes
2) Phagocyte places antigens on its surface
3) receptors on a specific T cell fit onto these antigens
4) this attachment causes t cells to rapidly divide by mitosis to form clones of genetically identical cells
5) Cloned T cells:
- develop into memory cells which respond rapidly to future invasion
- stimulate phagocytes to engulf pathogens
- stimulate B cells to divide and secrete antibody
- activate cytotoxic T cells

Question 6

How do cytotoxic T cells kill infected cells?

Answer 6

1) produce the perforin protein which makes holes in the cell surface membrane
2) The holes make cell freely permeable to all substances
3) cell dies