cells and the immune system Flashcards
what are antigens
cell surface membrane contains proteins that act as antigens.
antigens are molecules (usually proteins) that can generate an immune response when detected by the body
they are usually found on the surface of cells, including our own body cells
Antigens that aren’t normally found in the body are referred to as foreign antigens - it’s these antigens that the immune system usually responds to
what do antigens allow the immune system to identify
antigens allow the immune system to identify:
PATHOGENS
ABNORMAL BODY CELLS
TOXINS
CELLS FROM OTHER INDIVIDUALS OF THE SAME SPECIES
how are pathogens detected by the immune system
PATHOGENS
Pathogens are an organism that causes disease, e.g. bacteria, viruses and fungi
All pathogens have antigens on their surface -these are identified as foreign by immune systems, which then responds to destroy the pathogens
how are abnormal cells detected by the immune system
ABNORMAL BODY CELLS
Cancerous or pathogen-infected cells have abnormal antigens on their surface, which triggers an immune response
how are toxins detected by the immune system
TOXINS
These are poison. They’re also molecules, not cells. Some toxins are produced by bacteria e.g. the bacterium Clostridium botulinum releases a protein toxin that affects the nervous system, causing the symptoms of botulinum
The immune system can respond to toxins, as well as the pathogens released by them.
It’s important to know that the toxin itself is the antigen
how are cells from other individuals ( of the same species) of the same
when you receive cells form another person, such as in an organ transport or blood transfusion, those cells will have some antigens that are different to your own ( unless the donor is genetically identical to you)
The foreign antigens trigger an immune response. This response leads to the rejection of transplanted organs if drugs aren’t taken to suppress the recipients immune system
blood transfusion
-most important antigen are the ABO blood group antigens - if the donated blood contains A or B antigens that aren’t recognised by the recipients immune systems, they will generate an immune response
what are the body’s different defence mechanisms
if a pathogen is to infect the body, it must first gain entry
the body’s first defence is to form a physical or chemical barrier to entry e.g. skin
the next line ( if this fails) of defence is the white blood cells
what are the two types of white blood cells
- phagocytes
2. lymphocytes
what is phagocytosis
large particles such as some types of bacteria, can be engulfed by cells in vesicles formed from the cell surfaced membrane
This is called phagocytosis
what white blood cell carries out phagocytosis
the type of white blood cells that carries out phagocytosis are known as phagocytes
what are the stages of phagocytosis
- Chemical products/ the foreign antigens of pathogens or dead, damaged and abnormal cells act as attractants, causing phagocytes to move towards the pathogen (e.g. bacterium)
- phagocytes have several receptors on their cell - surface membrane that recognise and attach to chemicals/ antigens on the surface of the pathogen
- They engulf the pathogen to form a vesicle, known as a phagosome
- lysosomes move towards the vesicle and fuse with it
- Enzymes called lysozymes are present within the lysosome. These enzymes destroy ingested bacteria by hydrolysis of their walls
- the soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
- the phagocyte then presents the pathogen’s antigens on its surface to activate other immune systems. The phagocytes acting as an antigen-presenting cell
what are non- specific immune responses
non specific immune responses happen whatever the infection
e.g phagocytosis and skin barrier
what are specific immune responses
specific immune responses only react to specific antigens
what does the specific immune response depend on
the specific immune response depends on a type of white blood cell called a lymphocyte
how are lymphocytes produced
lymphocytes are produced by stem cells in the bone marrow. There are two types of lymphocytes each with its own role in the immune response
what are B lymphocytes (B cells)
B lymphocytes (B cells) are so called because they mature in the bone marrow.
They are associated with humoral immunity, that is immunity involving antibodies that are present in body fluids, or humour such as blood plasma
what are T lymphocytes ( T cells)
T lymphocytes are so called because they mature in the thymus gland. They are associated with cell - mediated immunity, that is immunity involving body cells
how can T - lymphocytes distinguish invader cells from normal cells
phagocytes that have engulfed and hydrolysed a pathogen present some of the pathogen’s antigen on their own cell -the 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 - surfaced membranes
what are antigen - presenting cells
cells that display foreign antigens on their surface are called antigen - presenting cells because they can present antigens of other cells on their own cell - surface membrane
what will T lymphocytes only respond to /what is cell - mediated immunity
T lymphocytes will only respond to antigens that are presented on a body cell ( rather than antigens within the body fluids)
This type of response is called cell - mediated immunity or the cellular response
why are the receptors on T lymphocytes important
receptors on T cells are important as it means that there are a vast number of different type of cells, each one responding to a different antigen
how do T lymphocytes respond to infection by pathogen
- Pathogens invade body cells or are taken in by phagocytes
- the phagocyte places antigens from the pathogen on its cell - surface membrane
- receptors on a specific helper T cell (T h cell) fit exactly on to these antigens
- this attachment activates the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
- The cloned T cells :
a) develop into memory cells that enable a rapid response to future infections by the same pathogen
b) stimulate phagocytes to engulf pathogens by phagocytosis
c) stimulate B cells to divide and secrete their antibody
d) activate cytotoxic T cells (Tc cells)
how do cytotoxic T cells kill infected cells
cytotoxic T cells kill abnormal cells and body cells that are infected by pathogens, by producing a protein called peforin that makes holes in the cell - surface membrane
These holes mean the cell membrane becomes freely permeable to all substances and the cell dies as a result
why is the action of T cells the most effective against viruses
the action of T cells is the most effective against viruses because viruses replicate inside cells
As viruses use living cells in which to replicate, the sacrifice of body cells prevent viruses multiplying and infecting