5.3 T-lymphocytes and cell-mediated immunity

Question 1

Define an antigen

Answer 1

Molecules present on the surface of cells which are recognised as non-self and stimulate an immune response

Question 2

Describe the differences between B and T lymphocytes

Answer 2

B- mature in the bone marrow. T- mature in the thymus gland.
B-Associated with humeral immunity. T- associated with cell-mediated immunity.

Question 3

Why can t-lymphocytes distinguish invader cells from normal cells

Answer 3

-Phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogens antigens on their own cell-surface membrane
-body cells invaded by a virus present some of the viral antigens on their own cell-surface membrane
- cancer cells present antigens on their cell-surface membrane
- transplanted cells from individuals of the same species have different antigens on their cell surface membrane

Question 4

Describe the process of cell-mediated immunity

Answer 4

1. Pathogens invade body cells or are taken in by phagocytes
2. Phagocytes present antigens from the pathogen on its cell-surface membrane
3. Receptors on a t-helper cell fit exactly into these antigens
4. This attachment activates the T cell to divide rapidly by mitosis and form genetically identical cells
5. The cloned T cells
   - develop into memory cells that allow a rapid response upon infection by the pathogen again
   - stimulate phagocytes to engulf pathogens by phagocytosis
   - stimulate b cells to divide and secrete their antibody
   - activate cytotoxic t-cells

Question 5

How to cytoxic t-cells kill infected cells?

Answer 5

Produced a protein called perforin that makes holes in the cell-surface membrane
These holes mean that the cell-surface membrane becomes freely permeable to all substances and the cells die as a result