T Lymphocytes and Cell-Mediated Immunity

Question 1

What is immunity?

Answer 1

The ability of organisms to resist infection by protecting against disease-causing microorganisms or their toxins that invade their bodies. It involves the recognition of foreign material (non-self).

Question 2

What are Antigens?

Answer 2

Part of an organism or substance that is recognised as non-self by the immune system and stimulates a immune response.

Question 3

Where are antigens located on the invading cells?

Answer 3

Antigens are usually proteins that are part of the cell-surface membrane or cell wall of the invading cells.

Question 4

What does the presence of an antigen trigger?

Answer 4

The production of an antibody as part of the body’s defence system.

Question 5

Where are lymphocytes produced?

Answer 5

By stem cells in the bone marrow.

Question 6

What produces specific immune responses and what is the nature of these responses?

Answer 6

Depend on lymphocytes. These are slower in action at first, but they can provide long term immunity.

Question 7

What produces non-specific immune responses?

Answer 7

Phagocytes.

Question 8

What are T Lymphocytes (T cells)?

Answer 8

They mature in the thymus gland. They are associated with cell-mediated immunity, immunity involving body cells. They respond to an organisms own cells that have been infected with non-self material.

Question 9

How can T lymphocytes distinguish invader cells from normal cells?

Answer 9

• Phagocytes present engulfed pathogens antigens on their own cell-surface membrane.
• Body cells invaded by a virus present viral antigens on their own cell-surface membrane.
• Transplanted cells have different antigens on their cell-surface membrane.
• Cancer cells present antigens on their cell-surface membranes.

Question 10

What are the cells that present antigens on their surface called?

Answer 10

Antigen-presenting cells because they can present antigens of other cells on their own cell surface membranes.

Question 11

What is a cell-mediated immunity response?

Answer 11

Where T Lymphocytes only respond to antigens that are presented on a body cell (rather than antigens within body fluid).

Question 12

What is the role of the receptors on T Cells?

Answer 12

The receptors on each T cell respond to a single antigen.

Question 13

How do T Lymphocytes respond to infection by a pathogen?

Answer 13

1. Pathogen invade cells or are taken in by phagocytes.
2. Phagocyte presents pathogens antigen on surface.
3. Receptors on a specific T helper Cell fit exactly to one of these antigens.
4. Attachment activates T cell to divide rapidly by mitosis and form a clone of genetically identical cells.
5. The cloned T cells:
   - develop into memory cells
   - stimulate phagocytes to engulf pathogens
   - stimulate B cells to divide and secret their antibody
   - activate cytotoxic T cells.

Question 14

What do cytotoxic T cells do?

Answer 14

They kill abnormal cells and body cells that are infected by pathogens, producing a protein called perforin that makes holes in cell-surface membranes.

Question 15

What is the significance of the holes in the cell-surface membranes as a result of perforin production?

Answer 15

They allow the cell membrane to be freely permeable to all substances, resulting in cell death.

Question 16

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

Answer 16

Because viruses replicate inside cells. As viruses use living cells to replicate, the sacrifice of body cells prevents viruses multiplying and infecting more cells.