5.3 T lymphocytes and cell-mediated immunity

Question 1

Define antigen

Answer 1

a molecule that triggers an immune response by lymphocytes

usually proteins that are part of the cell-surface membranes or cell walls of invading cells

Question 2

Where are lymphocytes produced?

Answer 2

By the stem cells in the bone marrow

Question 3

How do specific immune responses differ from non-specific immune responses?

Answer 3

They are slower in action but can provide long-term immunity.

Question 4

Where do B lymphocytes mature?

Answer 4

Bone marrow

Question 5

Where do T lymphocytes mature?

Answer 5

Thymus gland

Question 6

What are T lymphocytes associated with?

Answer 6

cell-mediated immunity, that is immunity involving body cells

Question 7

What are B lymphocytes associated with?

Answer 7

humoral immunity, that is immunity involving antibodies that are present in body fluids or ‘humour’ such as blood plasma

Question 8

How can T lymphocytes distinguish invader cells from normal cells?

Answer 8

1. phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogens antigens on their own cell surface membrane
2. body cells invaded by a virus present some of the viral antigens on their own CSM
3. transplanted cells from individuals of the same species have different antigens on their CSM
4. cancer cells are different from normal body cells and present antigens on their CSM

Question 9

What do you call cells that display foreign antigens on their surface?

Answer 9

Antigen-presenting cells

Question 10

Explain the type of response known as cell-mediated immunity or cellular response.

Answer 10

T lymphocytes will only respond to antigens that are presented on a body cell (rather than to antigens within the body)

Question 11

Explain the process of response of T lymphocytes to infection by a pathogen

Answer 11

1. pathogens invade body cells or are taken in by phagocytes
2. the phagocyte places antigens from the pathogen on its CSM
3. receptors on a specific helper T cell fit exactly onto these antigens
4. this attachment activated the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
5. the cloned T 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

Question 12

How do cytotoxic T cells kill infected cells?

Answer 12

1. kills abnormal cells and body cells that are infected by pathogens by producing a protein called ‘perforin’
2. perforin makes holes in the CSM meaning the cell membrane becomes freely permeable to all substances and the cell dies as a result