5.3 T lymphocytes and Cell-Mediated Immunity Flashcards
What is an antigen?
Any part of an organism or substance that is recognised as non-self (foreign) by the immune system and stimulates an immune response
What are antigens usually?
Proteins that are part of the cell-surface membranes or cell walls of invading cells such as microrganisms or abnormal body cells such as cancer cells
What does the presence of an antigen trigger?
Production of an antibody as part of the body’s defence systems
What is phagocytosis as an immune response?
Non-specific and occur whatever the infection
What are the advantages of specific responses?
Although they are slower in action they are specific to the infection and can provide long term immunity
What type of blood cell carries out specific immune responses?
Lymphocytes (type of white blood cell)
Where are lymphocytes produced?
In the bone marrow by stem cells
Why are B lymphocytes (B cells) names in such a way?
They mature in the bone marrow
What type of immunity are B lymphocytes associated with?
Humoral immunity
Where do T lymphocytes mature?
The thymus gland
What type of immunity are T cells involved in?
Cell-mediated immunity
In cell mediated immunity, what do lymphocytes respond to?
Organisms own cells that have been infected by non self material for a different species and cells from other organisms of the same species that are genetically different
What will cells that are from a different organism have?
Different antigens on their cell surface membranes from the organisms own cells
How do T lymphocytes distinguish between invader cells and own cells?
- phagocytes that have engulfed and hydrolysed a pathogen present some of the pathogens antigens on their own cell-surface membranes
- body cells invaded by a virus present some of the viral antigens on their own cell-surface membrane
- transplanted cells from individuals of the same species have different antigens on their cell-surface membrane
- cancer cells are different from normal body cells and present antigens on their cell-surface membranes
What are cells that display foreign antigens called?
Antigen-presenting cells because they can present antigens of other cells on their own cell surface membrane
What will T lymphocytes respond to?
Antigens present on body cells (rather than within body fluids)
What is t lymphocytes responding to antigens present on body cells known as?
Cell-mediated immunity or cellular response
What do the receptors on each T cell respond to?
A single antigen
(Response of T lymphocytes to infection by a pathogen)
What is the first stage?
Pathogens invade body cells or are taken in by phagocytosis
(Response of T lymphocytes to infection by a pathogen) stage 2, what does the phagocyte do?
Places antigens from the pathogen on its cell-surface membrane
(Response of T lymphocytes to infection by a pathogen) stage 3, what happens to the now antigen-presenting cell?
The receptors on a specific helper T cell fit exactly on to these antigens
(Response of T lymphocytes to infection by a pathogen) stage 4, what does the attachment of the specific helper T cell onto the antigens of the antigen presenting cell cause?
It activates the T cell to divide rapidly by mitosis and form a close of genetically identical cells
(Response of T lymphocytes to infection by a pathogen) what do the cloned T cells do?
- they develop into memory cells that enable a rapid response to future infections by the same pathogen
- they stimulate phagocytes to engulf pathogens by phagocytosis
- they stimulate B cells to divide and secrete their antibody
- activate cytotoxic T cells
What do cytotoxic T cells do?
They kill abnormal cells and body cells that are infected by pathogens
How do cytotoxic T cells kill infected cells
They produce a protein called performing that makes holes in the cell-surface membrane causing the cell membrane to be freely permeable to all substances and the cell dies as a result
What type of pathogen are T cells most effective against?
Viruses because viruses replicate inside cells
What type of cells do viruses use to replicate?
Living cells
What does the sacrifice of body cells prevent?
Viruses multiplying
Define antigen
A protein found on the cell surface membrane that triggers an immune response by lymphocytes
State two similarities between T cells and B cells
- both are white blood cells
- both have a role in immunity
- produced from stem cells
State two differences between T cells and B cells
- T cells mature in the thymus gland
- B cells mature in the bone marrow
- T cells are cell-mediated
- B cells are humoral immunity
