5.3 T lymphocytes and cell-mediated immunity

Question 1

What is antigen?

Answer 1

A molecule that triggers an immune response by lymphocytes.

Question 2

What are lymphocytes?

Answer 2

White blood cells that are responsible for the immune response. They become activated in the presence of antigens.

Question 3

What are the 2 types of lymphocytes?

Answer 3

1. T lymphocytes
2. B lymphocytes

Question 4

What are the characteristics of T lymphocytes?

Answer 4

1. mature in thymus gland
2. associated with cell-mediated immunity

Question 5

What will T lymphocytes only respond to?

Answer 5

Antigens that are presented on a body cell (rather than antigens within body fluids) .

Question 6

What is cell-mediated immunity or cellular response?

Answer 6

T lymphocytes only respond to antigens that are presented on a body cell.

Question 7

What are the stages of responses of T lymphocytes?

Answer 7

1. pathogens are taken in by phagocyte
2. phagocyte places antigens from pathogen on its cell-surface membrane
3. receptors on a specific helper T cell fits exactly onto these antigen
4. this attachment activates T cell to divide rapidly by mitosis and form a clone of genetically identical cells
5. the clone cells:
   ↳ develop into memory cells that enable a rapid response to future infections by the same pathogen
   ↳ stimulate phagocytes to engulf pathogens by phagocytosis
   ↳ stimulate B cells to divide and secrete their antibody
   ↳ activate cytotoxic T cells to kill infected cells

Question 8

How do cytotoxic T cells kill infected cells?

Answer 8

They kill infected cells by producing a protein called perforin that makes holes in the cell-surface membrane. These holes mean that the cell membrane becomes freely permeable to all substances and the cell dies as a result.

Question 9

Which type of pathogen are T cells most effective against? Why?

Answer 9

Viruses, because as viruses use living cells to replicate, the sacrifice of body cells prevents viruses multiplying and infecting more cells.