Immunology Flashcards
What is immunity
When the body’s defences prepared for a second infection from the same pathogen and can repel it before it causes any harm
Non specific mechanisms
Mechanisms that do not distinguish between one type of pathogen and another but respond to all of them in the same way these mechanisms isms act immediately and take two forms
A barrier to the entry of pathogens
Phagocytosis
Response is immediate and the same for all pathogens
Specific mechanisms
Do distinguish between different pathogens. The responses are less rapid but provide long lasting immunity. The responses involve a type of white blood cell called a lymphocyte and take two forms
Cell-mediated responses involving T lymphocytes
Humoral responses involving B lymphocytes
Response is slower and specific to each pathogen
What are lymphocytes and why is there a time lag
A type of white blood cell
Specific lymphocytes are not produced in response to an infection, but that they already exist. There’s so many different types that when a pathogen gets into the body one of these lymphocytes will have a protein on its surface that is complementary to one of the proteins of the pathogen. When an infection occurred the one type already present is stimulated to build up its numbers to a level where it can be effective. This explains why there’s a time lag between exposure to the pathogen and body’s defences bringing it under control.
What is the first line of defence against disease
Physical or chemical barrier next line of defence is phagocytes and lymphocytes which are types of white blood cells
Examples
- a protective covering - the skin covers the body surface providing a physical barrier that most pathogens find hard to penetrate.
- epithelia covered in mucus - many epithelial layers produce mucus which acts as a further defence against invasion. In the lungs, pathogens stick to this mucus, which is then transported away by cilia, up the trachea to be swallowed into the stomach.
- hydrochloric acid in the stomach this provides such low pH that the enzymes of most pathogens are denatured therefore the organism is killed.
What is an antigen
Usually a protein that protrudes from the cell surface membrane and is used in cell recognition . Antigens can be self or non self
They can generate an immune response
Usually found on the surface of cells including r body cells. Antigens that aren’t normally found in the body are called foreign antigens, it’s these antigens that the immune system usually responds to.
The presence of an antigen triggers the production of an antibody as part of the body’s defence system.
What is a pathogen
Organisms that cause disease e.g bacteria, virus and fungi. All pathogens have antigens on their surface- these are identified as foreign by immune system cells, which then respond to destroy the pathogen.
Abnormal body cells
Cancerous or pathogen- infected cells have abnormal antigens on their surface, which trigger an immune response.
Toxins
These are poisons. They’re also molecules, not cells. Some toxins are produced by bacteria e.g clostridium botulinum releases a protein toxin that affects the nervous system, causing the symptoms of botulism. The immune system can respond to toxins as well as the pathogens that release them.
The toxin itself is an antigen it doesn’t have antigens on its surface.
Receiving cells from other individuals of the same species
When you receive cells from another person, such as in an organ transplant or blood transfusion, those cells will have 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. For blood transfusions the most important antigens are the ABO blood group antigens- if the donated blood contains A or B antigens that aren’t recognised by the recipients immune system, they will generate an immune response.
What is phagocytosis Why can’t large particles like bacteria cross the cell surface membrane
They’re to large to cross cell surface membranes by diffusion or active transport. Instead they have to be engulfed by cells in the form of vesicles formed form the cell surface membrane. This is phagocytosis
What’s a phagocyte
A white blood cell
What’s phagocytosis
A process where a phagocyte engulfs and digests a pathogen
Where can phagocytes be found
Blood
In the alveoli
Lymph nodes
In infected tissue
What triggers a phagocyte to destroy a pathogen
Chemo attractant
What’s a phagosome
Is a vesicle- produced by Golgi , housing an engulfed pathogen that is formed when the cell surface membrane that invaginate sand engulfs
Describe the whole process of phagocytosis
1 Chemical products of the pathogen act as attractants, causing phagocytes to move towards the pathogen along a concentration gradient.
2 A phagocyte recognises the foreign antigens on a pathogen
3 Phagocytes attach themselves to the surface of the pathogen
4 the cytoplasm of the phagocyte moves round the pathogen engulfing it.
5 the pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte. Or say they engulf the pathogen to form a vesicle, known as a phagosome.
6 Lysosomes move towards the vesicle and fuse with it . Or say the lysosome fuses with the phagocytic vacuole.
7 lysozymes break down the pathogen. The process is the same as that for the digestion of food in the intestine, namely hydrolysis of larger insoluble food molecules into soluble ones.
8 the soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
9 the phagocyte then presents the pathogens antigens- it sticks the antigens on its surface to activate other immune system cells. The phagocyte is acting as an antigen presenting cell.
10 phagocytosis causes inflammation at the site of infection this swollen area contains dead pathogens and phagocytes.
What are B lymphocytes
Associated with humoral immunity. Produces antibodies mature in the bone marrow. Responds to foreign material outside body cells
Respond to bacteria and viruses.
T lymphocyte
Associated with cell mediated immunity
Mature in the Thymus gland
Responds to foreign material inside body cells
Responds to own cells altered by viruses or cancer and to transplanted tissues.
How can a T cell distinguish normal cells from invader cells
Phagocytes that have engulfed and broken down a pathogen present some of the pathogens antigens on their own cell surface membrane
Body cells invaded by a virus also manage to present some of the viral antigens on their own cell surface membrane as a sign of distress
Cancer cells likewise present antigens on their cell surface membranes
Why is it called cell mediated immunity
T cells will only respond to antigens that are attached to a body cell not cells within body fluids
What do T cells actually do
Has receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes. This activated the T cell.
Helper T cells release chemical signals that activate and stimulate phagocytes and cytotoxic T cells which kill abnormal and foreign cells.
Cell mediated immunity/ cellular response
Identified with killing infected body cells to free viruses for destruction by antibodies and phagocytosis .
- also works against cancerous/tumour cells and to expose intracellular bacteria hiding between body cells.
Model answer
1 a phagocyte or macrophage engulfs and digests a virus placing viral antigens on its cell surface membrane , its now an antigen presenting cell
2 a body cell becomes infected by the same virus and some viral antigens are placed on its cell surface membrane this body cell is also an antigen presenting cell.
3 a helper T cell specific to that viral antigen binds to the antigen presenting phagocyte.
4 the phagocyte now releases a chemical (called interleukin 1) that activates/stimulates/ triggers the helper T cell.
5 the helper T cell now releases a chemical (interleukin 2) that enters the honours (blood, tissue fluid, lymph) and activates a cytotoxic T cell, also specific to the viral antigen.
6 the cytotoxic T cell divides by mitosis to form many clones some of which travel to the site of infection.
7 each activated cytotoxic T cell binds to an infected cell and releases a chemical perforin that puts holes into the cells membrane and an influx of water bursts the cell, killing it.
8 freed viruses can now be dealt with by the humoral response and phagocytosis.
Four things that result from the response of T lymphocytes
- Produces memory cells that circulate in the blood and tissue fluid in readiness to respond to a future infection by the same pathogen.
- stimulates B cells to divide
- stimulates phagocytosis by phagocytes
- kills infected cells by making holes in their cell surface membrane
