5.3) T-lymphocytes and cell-mediated immunity

Question 1

What is immunity?

Answer 1

Immunity is the ability to resist infection by protecting against disease-causing microorganisms

Question 2

What is an antigen?

Answer 2

A molecule (protein) that triggers and immune response

Question 3

What does the presence of an antigen do?

Answer 3

It triggers the production of an antibody as part of the body’s defence system

Question 4

What are the two types of lymphocyte?

Answer 4

• T-lymphocyte (T-cell)
• B-lymphocyte (B-cell)

Question 5

Where do B-lymphocytes (B-cell) mature?

Answer 5

Bone marrow

Question 6

Where do T-lymphocytes (T-cell) mature?

Answer 6

Thymus gland

Question 7

What is involved with humoral immunity?

Answer 7

Antibodies that are present in body fluid

Question 8

What is involved with cell -mediated immunity?

Answer 8

Body cells

Question 9

How can T-cells distinguish invader cells from normal cells?

Answer 9

Phagocytes that have engulfed an hydrolysed a pathogen present some of the pathogen’s antigens on their own cell surface membrane

Body cells invaded by a virus present the viral antigens on their own cell surface membrane

Transplanted cells from individuals of the same species present antigens on their cell surface membrane

Cancer cells are different from body cells and present antigens on their cell surface membrane

Question 10

What are antigen-presenting cells?

Answer 10

Cells that display antigens of other cells on their own cell surface membrane

Question 11

What does T-cells only respond to?

Answer 11

Antigens that are presented on a body cell

Question 12

What is the role of the receptors on each T-cell?

Answer 12

To respond to a single antigen

Question 13

What are the stages in the response of T-lymphocytes to infection by a pathogen:

1.
2.
3.
4.
5.
a)
b)
c)

Answer 13

1. Pathogen invades body cells or is taken in by phagocytes
2. The phagocyte places antigens from the pathogen on its cell surface membrane
3. Receptors on a specific T-helper cell, fit exactly onto antigens
4. Attachment activates T-helper cells to divide rapidly by mitosis and form a clone of genetically identical cells
5. The clone T cells:

• Memory cells
• Stimulate phagocytes
• Stimulate B-cells to divide and secrete antibodies
  *Activate cytotoxic T cells

Question 14

What is the role of a cytotoxic T cell?

Answer 14

To kill abnormal cells and body cells that are infected by pathogens by producing a protein called ‘perforin’

Question 15

What protein does cytotoxic T-cells produce?

Answer 15

Perforin

Question 16

What is the role of the protein cytotoxic T-cells produce?

Answer 16

To make holes in the cells-surface membrane, this means the cell membrane becomes freely permeable to all substances and the cell will die

Question 17

Why is the action of T-cells most effective against viruses?

Answer 17

Because viruses replicate inside cells
- Viruses use living cells to replicate
- Killing body cells prevents viruses multiplying and infecting more cells