5.3 - T Lymphocytes and cell mediated immunity

Question 1

What are antigens

Answer 1

Any part of an organism/substance that is recognised as non-self by the immune system
—> stimulating an immune response
—> antigens are usually proteins on the surface of invading cells

Question 2

What does the presence of antigens trigger

Answer 2

Presence of antigens triggers a production of antibodies or other specific immune response

Question 3

What are the 2 types of lymphocytes and where do they develop

Answer 3

• T cells: produced in bone marrow, mature in thymus gland
• B cells: produced and matured in bone marrow

Question 4

Where can you find antigens

Answer 4

The surface of
- Pathogens
- Transplanted cells
- Cancer cells

Question 5

How can T lymphocytes distinguish invader cells from normal cells

Answer 5

• phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogen’s antigens on their own CSM
• body cells invaded by a virus present some of the viral antigens on their own CSM
• transplanted cells from individuals of the same species have different antigens on their CSM
• Caner cells are different from normal body cells and present antigens on their CSM

Question 6

What is antigen presentation

Answer 6

• After phagocytosis, phagocytes display the antigens of foreign cells on their CSM
• this is called antigen presentation and they are now antigen presenting cells (APCs)
• T-helper cells only respond to antigens present on other cells

Question 7

What is cell-mediated immunity

Answer 7

When the T helper lymphocytes only respond to antigens that are presented on a body cell

Question 8

Describe the steps in Cell-mediated immunity that Th cells do

Answer 8

• Each Th cells has a specific receptor to different types of antigens
• the th cell binds to the complementary antigen presented on the phagocyte
• this activates it to divide rapidly by mitosis making clones of the required specific Th cell = clonal selection
• the clonal Th cells produce cytokines which stimulate more responses

Question 9

What are the responses that the cloned T cells cause

Answer 9

• produce cytokines that stimulate more phagocytosis
• produce cytokines that stimulate the division of B cells for antibody production
• develop into T memory cells, which give a rapid response if this pathogen invades the body again
• Activation of T cytotoxic cells
  —> this is called the cascade defect

Question 10

What do cytotoxic cells do

Answer 10

• kill abnormal cells and any infected body cells
• they produce a protein called perforin
• it makes holes in CSM, compromising the cell
• the holes means = cell membrane becomes freely permeable to all substances and the cell dies as a result

Question 11

What are all the stages involved in Cell-mediated immunity

Answer 11

• process begins with phagocytosis and then antigen presentation (APC)
• everywhere all the APC travels in the blood, it can present these antigens to T-helper cells
• If the T-cell receptors on the membrane of the T-helper cells is complementary to to the antigen on the APC, the T-helper cell = an actives T-cell and begins to divide by mitosis (clonal selection)
• the APC has to find the specific T-helper cell with the right TCR, therefore there’s a time lag before the immune system starts to respond to the infection
• this clonal selection of the activated T-cell stimulates other types of responses:
  1) produce cytokines that stimulate more phagocytosis
  2) produce cytokines that stimulate the division of B cells for antibody production
  3) develop into T memory cells, which give a rapid response if this pathogen invades the body again
  4) Activation of T cytotoxic cells

Question 12

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

Answer 12

• because viruses use living cells in which to replicate
• the sacrifice of body cells prevents viruses multiplying and infecting more