T lymphocytes and cell mediated responses Flashcards
What type of response does the body have to initial infection, does this type of response change depending on the type of infection?
The body’s initial response to infection is non - specific, meaning it responds the same way to all types of infections, regardless of the pathogen
What is immunity?
Immunity is the ability of an organism to resist infection by identifying and defending against pathogens or their toxins
What are the two main phases of the immune response?
- Non - specific response, which is the initial defence against an infection
- Primary immune response, which triggers long term immunity by producing antibodies
What is an antigen?
Antigens can be any foreign substance that is recognised by the immune system and triggers an immune response
What role do antigens play in immunity?
Antigens stimulate the production of antibodies as part of the body;s defence system
What are antigens usually made of?
Antigens are usually proteins found on cell surface membranes or cell walls of invading cells
What types of cells can display antigens?
Antigens can be found on pathogens (bacteria + viruses), abnormal body cells (cancer cells) and cells from other organisms (organ transplants)
Where are lymphocytes produced?
In the bone marrow from stem cells
What are the two types of lymphocytes, where do these lymphocytes mature?
B lymphocytes - matured in the bone marrow
T lymphocytes - matured in the thymus gland
What are lymphocytes?
A type of white blood cell involved in the specific immune response
What type of immunity do B cells provide?
Humoral immunity, which involves antibodies in bodily fluids eg. blood plasma
What type of immunity do T cells provide?
Cell - mediated immunity, which involves interactions with body cells eg infected cells
What is cell mediated immunity?
The immune response involving T lymphocytes, which respond to antigens displayed on body cells
Why do T lymphocytes respond to an organism’s own cells?
This is because they may be infected by a pathogen or display foreign antigens
Give four examples of cells that T lymphocytes can recognise as non - self
- Phagocytes that have engulfed and hydrolysed a pathogen
- Virus - infected cells displaying viral antigens
- Transplanted cells from a genetically different individual
- Cancer cells with abnormal antigens
What are antigen - presenting cells? (APCs)
Cells that display foreign antigens on their cell - surface membrane, triggering an immune response
Why are T cells described as specific in their response?
This is because each T cells has receptors that respond to a single specific antigen
What is the first step in the response of T lymphocytes to infection?
Pathogens invade body cells or are engulfed by phagocytes
How do phagocytes trigger a T cell response?
They place antigens from the pathogen on their cell - surface membrane
How do T helper cells (Th cells) recognise infected cells?
Their receptors fit exactly onto the presented antigens on the antigen presenting cells
What happens after a T helper cell binds to an antigen?
It is activated to divide rapidly by mitosis, forming a clone of identical cells
What are the four key roles of cloned T cells?
1) Develop into memory cells for future immunity
2) Stimulate phagocytes to engulf pathogens
3) Stimulate B cells to divide and produce antibodies
4) Activating cytotoxic T cells to kill infected cells
Outline the 5 stages involved in the response of T lymphocytes to infection by a pathogen
1) Pathogens will invade the body’s cells or are taken in by phagocytes
2) The phagocyte places antigens from the pathogens on its cell - surface membrane
3) Receptors on a specific helper T cell fit exactly onto these antigens
4) This attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
5) The cloned T cells:
A. Develop into memory cells that enable a rapid response future infections by the same pathogens
B. Stimulate phagocytes to engulf pathogens by phagocytosis
C. Stimulate B cells to divide and secrete their antibodies
D. Activate cytotoxic T cells
How do cytotoxic cells kill infected cells?
They produce perforin, a protein that create holes in the cell membrane
What is the function of cytotoxic T cells (Tc cells)?
They kill abnormal or infected cells by breaking down their cell membranes
What happens when perforin forms holes in the infected cell?
The membrane becomes freely permeable, leading to cell death
Why is the action of cytotoxic T cells, particularly effective against viruses
Viruses replicate inside host cells, so killing the infected cell prevents viral replication and stops further infection
