Cell recognition and the Immune System Flashcards
What’s an infection
interaction between the pathogen and the bodies defence mechanisms
What’s immunity
Having overwhelmed the pathogen the body’s defences seem to be better prepared for a second infection from the same pathogen and can kill it before it causes any harm
Defence mechanisms
Longer lasting 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
Recognising your own cells
To defend the body, lymphocytes must be able to distinguish the body’s own cells (self) from those that are foreign (non-self)
- each cell, self or non self has specific molecules on its surface that identify it, they may have proteins on its surface, proteins have variety and tertiary structure. it’s the variety of specific 3-D structure that distinguish one cell from another
These protein molecules which usually allow the immune system to identify:
- pathogens e.g HIV
- non self material such as cells from other organisms of the same species
- toxins including those produced by certain pathogens
- abnormal body cells such as cancer cells
> specific lympocytes are not produced in response to an infection but they already exist
Stages in recognising
1) identification in removing the threat they pose
2) immune system recognises these as non self even though they have come from individuals of the same species
3) it attempts to destroy the transplant
When destroying the pathogen
the lymphocyte will most likely have a protein on the surface that’s complementary to one of the proteins of the pathogen
Clonal selection
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 point where it can be effective in destroying it
How lymphocytes recognise cells belonging to the body
- in the fetus, lymphocytes are constantly colliding with other cells
- some of the lymphocytes will have receptors that exactly fit those of the body’s own cells
- These lymphocytes either die or are suppressed
- no clones of these anti-self lymphocytes will appear in the blood, leaving only those that might respond to non- elf antigens
two types of white blood cell
phagocytes and lymphocytes
Phagocytosis
- chemicals of pathogens or dead cells act as attractants causing phagocytes to move towards the pathogen
- phagocytes have several receptors on their cell surface membrane that recognise and attach to chemicals on the surface of the pathogen
- they engulf the pathogen to form a vesicle known as phagosome
- lysosomes move towards the vesicle and fuse with it
- lysozymes are present within the lysosome. they destroy ingested bacteria by hydrolysis of cell walls
- the soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
Antigens
foreign proteins that stimulate an immune response
- Antigens are part of cell surface membranes on invading cells
- presence of an antigen triggers the production of an antibody as part of the defence system
Lymphocytes
- phagocytosis is a non specific response
- the body has specific responses that react to specific antigens, they’re slow but provide long term immunity
- Lymphocytes are produced by stem cells in the bone marrow and there are two types of Lymphocytes:
- B Lymphocytes (B cells) are associated with humoral immunity involving antibodies that are present in body fluids or ‘humour’ such as blood plasma
- T Lymphocytes they’re present in thymus gland. There associated with cell mediated immunity
T Lymphocytes can distinguish these invader cells from normal cells
- phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogen’s antigens on their own cell surface membrane
- body cells invaded by a virus present some of a viral antigens on their own cell 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 surface membranes
cells that display foreign antigens on their surface are called
antigen-presenting cells
What response is when T Lymphocytes will only respond to antigens that are presented on a body cell
Cell mediated or cellular response
The role of receptors on T cells
- the receptors on each t cell respond to a single antigen
Stages in response of T Lymphocytes to infection by a pathogen
- pathogen invade body cells
- phagocyte places antigen from the pathogen on its cell surface membrane
- receptors on a specific helper T cell fit exactly onto these antigens
- The attachment of T cell to divide rapidly by mitosis and form a clone of genetically identical cells
- The cloned T cells:
> develop into memory cells that enable a rapid response
> stimulate phagocytes to engulf pathogens by phagocytosis
> stimulate B cells to divide and secrete their antibody
> activate cytotoxic T cells