5.3 T lymphocytes and cell-mediated immunity

Question 1

What is an antigen

Answer 1

Any part of an organism or substance that is recognised as non-self by the immune system and stimulates an immune response

They are usually proteins that are part of the cell-surface membranes or cell walls of invading cells. The presence of an antigen triggers the production of an antibody as part of the body’s defence system

Question 2

What type of response is phagocytosis

Answer 2

Non-specific, occurs whatever the infection

Question 3

What type of response is the cellular response

Answer 3

Specific, which react to specific antigens

Question 4

Where are lymphocytes produced

Answer 4

By stem cells in the bone marrow

Question 5

What are the two types of lymphocytes

Answer 5

1. B Lymphocytes (Bone marrow)

2. T lymphocytes (Thymus gland)

Question 6

What are B lymphocytes involved in

Answer 6

Humoral immunity, immunity involving antibodies that are present in body fluids

Question 7

What are T lymphocytes involved in

Answer 7

Cell mediated immunity, immunity involving body cells

Question 8

How do T lymphocytes distinguish invader cells from normal cells

Answer 8

1. Phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogen’s antigens on their own cell membrane
2. Body cells invaded by a virus present some of the viral antigens on their own cell membrane
3. Transplanted cells from individuals of the same species have different antigens on their cell membrane
4. Cancer cells are different from normal body cells and present antigens on their cell membrane

Question 9

What are cells called that display foreign antigens on their surface

Answer 9

Antigen-presenting cells

Question 10

What will T lymphocytes only respond to

Answer 10

Antigens that are present on a body cell (rather than to antigens within the body fluids)

Question 11

What is the process of cell mediated immunity

Answer 11

1. Pathogens invade body cells or are taken in by phagocytes
2. The phagocyte places antigens from the pathogen on its cell membrane
3. Receptors on a specific helper T cell fit exactly onto these antigens
4. This attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
5. The cloned T cells:

a) Develop into memory cells that enable a rapid response to future infections by the same pathogen
b) Stimulate B cells to divide and secrete their antibody
c) Stimulate phagocytes to engulf pathogens by phagocytosis
d) Activate cytotoxic cells

Question 12

How do cytotoxic T cells kill infected cells

Answer 12

They produce a protein called perforin that makes holes in the cell membrane. These holes mean the cell is freely permeable and therefore dies