Immunity Flashcards
The human body has a range of defences to protect itself from pathogens- some are general and immediate defences such as
- The skin forming a barrier of entry of pathogens
- phagocytosis
Some defences are specific, less rapid however
Longer-lasting
Specific responses involve a type of white blood cell called a
Lymphocyte
What are the 2 types of lymphocyte?
T lymphocyte and B lymphocyte
T lymphocytes are involved in
Cell-mediated response
B lymphocytes are involved in
Humoral response
To defend the body from invasion by foreign materials, lymphocytes must be able to distinguish the body’s own cells and molecules (self) from
Those that are foreign (non self)
What would happen if lymphocytes could not distinguish cells and molecules that are self and non self?
The lymphocytes would destroy the organism’s own tissues
Each type of cell has specific molecules on its surface that identify it. These molecules include
Proteins
What do proteins on cell surfaces enable the immune system to identify?
- pathogens e.g. HIV
- non-self materials such as cells from other organisms of the same species
- toxins (including those produced by certain pathogens like the bacterium that causes cholera)
- abnormal body cells such as cancer cells
Why does the immune system attempt to destroy organ or tissue transplants?
The immune system recognises these as non-self, even though they come from individuals of the same species; it therefore attempts to destroy the transplant.
What is done to minimise the effect of tissue rejection?
- Donor tissues for transplant are normally matched as close as possible to those of the recipient. The best matches often come from relatives that are genetically close.
- immunosuppressant drugs are often administered to reduce the levels of immune response
What is clonal selection?
When an infection occurs, the one type of lymphocyte already present that has complementary proteins to those of the pathogen is stimulated to divide to build up its numbers to a level where it can be effective in destroying it
Why is clonal selection necessary?
With so many different types of lymphocytes, there are very few of each type
Colonial selection explains why there is a lag time between exposure to the pathogen and ___ _____ ______ in brining it under control
The body’s defence
Explain how lymphocytes recognise cells belonging to the body
- approximately around 10 million lymphocytes present at any time, each capable of recognising a different chemical shape
- in the foetus, these lymphocytes are constantly colliding with other cells and because infection in the foetus is rare (protected from outside world and by placenta) lymphocytes will collide almost exclusively with the body’s own material (self)
- some of the lymphocytes will have receptors that exactly fit those of the body’s own cells and these lymphocytes either die or are suppressed
- only remaining lymphocytes are those that might fight fit foreign material (non-self) and therefore only respond to foreign material
- in adults, any lymphocytes produced in the bone marrow initially only encounter self-antigens
- any lymphocyte that shows an immune response to these self-antigens undergo programmed cell death (apoptosis) before they can differentiate into mature lymphocytes
- no clones of these ‘anti-self’ lymphocytes will appear in the blood, leaving only those that might respond to non-self antigens
If first line of defence fails (physical or chemical barrier), the next line of defence is
The white blood cells
2 types of white blood cell
- lymphocytes (involved in immune response)
- phagocytes (involved in phagocytosis)
Explain the stages of phagocytosis
1- phagocytes is attracted to the pathogen by the chemical products of the pathogen. The phagocytes moves towards the pathogen along a concentration gradient
2- phagocytes has several receptors in its cell surface membrane that attach to chemicals on the surface of the pathogen
3- phagocyte engulfs pathogen to form a vesicle known as a phagosome
4- lysosomes within the phagocyte migrate towards the phagosome
5- lysozymes are present within the lysosome; these lysozymes destroy ingested bacterium by hydrolysis of their cell wall
6- the soluble products from the break down of the pathogen are absorbed into the cytoplasm of the phagocyte
The initial response of the body to infection is non-specific(phagocytosis) the next stage is
The primary immune response that confers immunity
What is immunity?
Ability of organisms to resist infection by protecting against disease- causing microorganisms or their toxins that invade the body. It involves the recognition of foreign material (antigens)
What is an antigen?
Molecules (usually proteins) that generate an immune response when detected by the body as they are recognised as non-self (foreign) by the immune system and stimulates an immune response
Antigens are usually ___ that are part of the cell-surface membranes or cell walls of invading cells, such as microorganisms or abnormal body cells such as cancer cells
Proteins
The presence of an antigen triggers the production of
An antibody as part of the body’s defence system