5.3: T-Lymphocytes and Cell-Mediated immunity

Question 1

What is an antigen?

Answer 1

An antigen is any part of an organism that is foreign and stimulate an immune response

Usually proteins on the membrane or cell wall of an invading cell. They lead to the production of antibodies

Question 2

What are the two types of Lymphocytes

Answer 2

T-Lymphocytes - Mature in the Thymus gland and are associated with Cell-Mediated immunity and body cells

B-Lymphocytes - Mature in the Bone marrow and are associated with Humoral immunity (involve antibodies in blood plasma and bodily fluids)

Question 3

How can T-Lymphocytes distinguish invader cells

Answer 3

1. Phagocytes that have engulfed a pathogen present some of the pathogens antigens on their cell-surface membrane
2. Body cells that have been invades present some of the viral antigens on their own membrane
3. Transplanted cells of individuals have different antigens
4. Cancer cells are different and present antigens on their CSM

Question 4

What do T-Lymphocytes respond to

Answer 4

T-Lymphocytes only respond to antigens presented on a body cell, rather than antigens in body fluids. This is a CELLULAR RESPONS

Question 5

Significance of receptors on T-Cells

Answer 5

There are millions of T-Cells, each corresponding to a different antigen. The receptors respond to a single anitgen

Question 6

Cell Mediated Response

Answer 6

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

• Divide into memory cells to enable a rapid response to future infections
• Stimulate phagocytes to engulf pathogens by phagocytosis
• Stimulate B Cells to divide and secrete their antibody
• Activate cytotoxic T cellls

Question 7

What 4 things can cloned T cells do during the cellular response

Answer 7

1. Divide into memory cells to enable a rapid response to future infections
2. Stimulate phagocytes to engulf pathogens by phagocytosis
3. Stimulate B cells to divide and secrete their antibody
4. Active Cytotoxic T cells which produce perforin to make the membrane freely permeable

Question 8

How do Cytotoxic T cells kill infected cells

Answer 8

Cytotoxic T cells produce a protein called perforin that makes holes in the cell surface membrane.

These holes mean the cell membrane becomes freely permeable to all substances and the cell dies.

This shows the important of a cell surface membrane

Question 9

What is the action of T cells the most effective against

Answer 9

Viruses, because viruses replicate inside cells and the destruction of a body cell stops the replication and infection of more cells