3.2.4 Cell recognition and the immune system Flashcards
Antigens
What type of molecules may these be
Proteins
Antigens
What they enable the immune system to identify
- pathogens
- cells from other organisms of the same species
- abnormal body cells
- toxins
Pathogen
Definition
-microorganism that causes disease
Pathogen
ways in which it may cause disease when it has entered the body
- produces toxins
- damages/kills cells
Toxin
Definition
-poisons (molecules, not cells)
Types of defence mechanisms
- non-specific
- specific
Non-specific defence mechanisms
- immediate response
- same for all pathogens
Non-specific defence mechanisms
Examples
Physical barrier
└e.g. skin, mucus, saliva
Phagocytosis
└engulfing of large particles
Specific defence mechanisms
- slower response
- specific to each pathogen
Specific defence mechanisms
Examples
-cell mediated response
└T lymphocytes
-humoral response
└B lymphocytes
Lymphocytes
Where produced
- bone marrow
- as stem cells
B lymphocyte (B cells)
-mature in bone marrow
-associate with humoral immunity
└involving antibodies present in body fluids such as blood plasma
-act by infections in blood
T lymphocyte (T cells)
-mature in thymus gland
-associated with cell-mediated immunity
└immunity involving body cells
-act in response to infected cells
Antigen
Definition
-a protein that causes an immune response
Antigen
Location
-cell surface membranes/cell walls of invading cells
Antigenic variation
-pathogens can change their surface antigens due to change in their genes
Antigenic variation effect
- have to do primary response as memory cells for secondary response won’t recognise new antigens
- difficult to develop vaccines
Disease
Definition
-collection of symptoms
└not organisms
Phagocytosis of pathogens
Process
- phagocyte recognises antigens on the pathogen as foreign
- it is attracted to the pathogen by chemicals
- the pathogen is then engulfed
- and enclosed in a vesicle
- the vesicle fuses with a lysosome
- which contains hydrolytic enzymes
- which hydrolyse/digest the pathogen
Phagocyte
Location
- some travel in blood
- some leave and migrate to the site of the infection
EQ: structures a bacterial cell may have that a white blood cell does not have
- Cell wall
- Capsule / slime layer
- Circular DNA
- Naked DNA / DNA without histones
- Flagellum
- Plasmid
- Pilus
- 70s / smaller ribosomes
- Mesosome
Neutrophil structure
-lobed nucleus
Neutrophil/phagocyte function
-phagocytosis/engulfing
Lymphocyte structure
-large nucleus
Lymphocyte function
-produce antibodies
T cell and B cell
Similarities
- both are types of white blood cell
- both are produced from stem cells
T cell and B cell
Differences
- b cells = bone marrow
- t cells = thymus gland
- t cells are involved in cell-mediated immunity
- b cells are involved in humeral immunity
The cellular response
The response of T lymphocytes to a foreign antigen
Antigen presenting cells
Definition
cells displaying foreign antigens on their cell-surface membrane
Antigen presenting cells
Process
-phagocyte recognises antigens on the pathogen as foreign
-it is attracted to the pathogen by chemicals
-the pathogen is then engulfed
-and enclosed in a vesicle
-the vesicle fuses with a lysosome
-which contains hydrolytic enzymes
-which hydrolyse/digest the pathogen
-PAGOCYTE PRESENTS PATHOGENS ANTIGENS ON SURFACE
CAN ACTIVATE OTHER IMMUNE SYSTEM CELLS
T cells
what they respond to
-organism’s own cells that have been infected by non-self material
-cells from another individual of the same species that are genetically different
└e.g. transplanted material
└as have different antigens on their cell-surface membrane from the antigens on the organism’s own cells
T cells
How they distinguish between self and non self cells
- phagocytes present some antigens of the pathogen they have engulfed and hydrolysed on own cell-surface membrane (antigen presenting cells)
- body cells invaded by a virus present some viral antigens on 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 membrane
The cellular response
Stages
-pathogens invade body cells
└phagocytes engulf pathogens
-phagocyte presents antigens from pathogen on cell-surface membrane= antigen presenting cell
-receptors on a specific helper T cell (Th)
└fit exactly onto these antigens
-= activates T cell to divide rapidly by mitosis and form clone cells (genetically identical)
-cloned T cells:
└form memory cells
└enable rapid response to further infections by the same pathogen
└stimulate phagocytosis
└phagocytes to engulf pathogens
└stimulate B cells to divide and produce their antibody
└activate cytotoxic T cells (Tc cells)
T cells
- type of white blood cell
- receptor proteins on its surface that can bind to complimentary antigens presented by phagocytes = activates T cell
TH cells
Release chemical signals to activate and stimulate phagocytes, TC cells and B cells
cytotoxic T cells (TC cells)
what they kill
- abnormal cells
- body cells that are infected by pathogens
cytotoxic T cells (TC cells)
how they kill
-produce protein called perforin
└makes holes in the cell-surface membrane
└=membrane becomes freely permeable to all substances
└=cell dies
Why is it an issue that T cells are most effective against virus replicating inside cells
-viruses use living cells to replicate
└so sacrifice body cells prevents viruses multiplying and infecting more cells
The cellular response
B cells
- can be activated by Th cells
- secrete antibodies
The cellular response
phagocytes
- can be activated by Th cells
- phagocytosis
EQ: Explain the increase in specific plasma cells and antibody in people infected with the Ebola virus.
- the antigen on Ebola binds to and stimulates a specific B cell
- which causes replication/cloning of the B cell
- B cells produce antibodies
