T-lymphocytes and cell-mediated immunity Flashcards
Define immunity.
The ability of organisms to resist infection by protecting against disease-causing microorganisms or their toxins that invade their bodies.
Define an antigen.
An antigen is any part of an organism or substance that is recognised as non-self by the immune system and stimulates an immune response.
Antigens are usually proteins that are part of the cell surface membrane or cell wall of the invading cell.
What are lymphocytes?
Lymphocytes are a type of WBC that provides a specific immune response, they are slower in action at first but they can provide long term immunity.
Where are lymphocytes produced?
By stem cells in the bone marrow.
What are the 2 types of lymphocytes and what are the roles in immune response?
B lymphocytes (B cells):
- Matured in the BONE marrow.
- Associated with humoral immunity (immunity that involves antibodies).
T lymphocytes (T cells):
- Matured in the THYMUS gland.
- Associated with cell-mediated immunity (immunity that involves body cells).
What do lymphocytes do in immune response?
Respond to an organism’s own cells that have been infected by non-self material from a different species e.g. a virus.
They also respond to cells from the same species but are genetically different. Those, therefore, would have different antigens on their cell surface membrane from the antigens on the organism’s own cells.
How can T-lymphocytes differentiate invader cells and normal cells?
- Phagocytes that have engulfed and hydrolysed a pathogen will present some of the pathogen’s antigen on its own cell surface membrane.
- Body cells that are invaded by viruses will present some of the viral antigens on their own cell surface membrane.
- Transplanted cells will have different antigens on their cell surface membrane from the organism’s own cells.
- Cancer cells are different from normal cells, therefore, it presents the antigens on its cell surface membrane.
What is the name of the cells that display antigens on their surface?
Antigen-presenting cells because they present the antigens of other cells on their own cell surface membrane.
When will T-lymphocytes respond?
They only respond to antigens that are presented on the body cell, rather than the antigens within the body fluid.
The type of response is called cell-mediated immunity or cellular response.
Why are the receptors on T-cells important?
Because receptors on each T cell responds to a single antigen because there’s a vast number of different types of T-cells.
Describe the stages of a T-cell response to infection by a pathogen.
1) Pathogens invade body cells or taken in by phagocytes.
2) The phagocyte presents the antigens onto its cell surface membrane.
3) Receptors on a specific helper T cell (Th cell) fits exactly onto these antigens.
4) The attachment to the T cell activates it to rapidly divide by mitosis and form clones of genetically identical cells.
5) The cloned T cells will:
* Develop into memory cells so it can rapidly respond if the same pathogen infects in the future.
* Stimulates B cells to divide and secrete antibodies.
* Stimulates phagocytes to engulf pathogens by phagocytosis.
* Activate cytotoxic T cells (Tc cells).
What are cytotoxic T cells?
Tc cells kill abnormal cells and body cells that are infected by pathogens.
How do cytotoxic T cells kill pathogens?
They produce a protein called perforin that makes holes in the cell surface membrane which will allow the cell membrane to become freely permeable to all substances and cell dies as a result.
Why is the action of T cells the most effective against viruse?
Because viruses replicate inside cells and they use living cells to replicate so the sacrifice of body cells will prevent virus multiplying and infecting more cells.
