Topic 11.1: Defence Against Infectious Disease Flashcards
Define clotting
is a mechanism that prevents the loss of blood from broken vessels
Describe the process of blood clotting (7)
Clotting (haemostasis) is a mechanism that prevents the loss of blood from broken vessels
Damaged cells and platelets release chemical signals called clotting factors which trigger a coagulation cascade:
Clotting factors convert the inactive zymogen prothrombin into the activated enzyme thrombin
Thrombin catalyses the conversion of the soluble plasma protein fibrinogen into an insoluble form (fibrin)
Fibrin forms an insoluble mesh of fibres that trap blood cells at the site of damage
Clotting factors also cause platelets to become sticky, which then adhere to the damaged region to form a solid plug called a clot
The clot prevents further blood loss and blocks entry to foreign pathogens
What is the purpose of clotting factors?
Clotting factors convert the inactive zymogen prothrombin into the activated enzyme thrombin
What does thrombin do?
Thrombin catalyses the conversion of the soluble plasma protein fibrinogen into an insoluble form (fibrin)
What does fibrin do?
Fibrin forms an insoluble mesh of fibres that trap blood cells at the site of damage
Outline the principle of challenge and response (4)
When the body is challenged by a foreign pathogen it will respond with both a non-specific and specific immune reaction
The body is capable of recognising invaders as they do not possess the molecular markers that designated all body cells as ‘self’ (MHC class I)
Non-specific immune cells (macrophages) present the foreign antigens to lymphocytes as examples of ‘non-self’ (on MHC class II)
These lymphocytes can then respond with the production of antibodies to destroy the foreign invaders
Outline the principle of clonal selection (4)
Each B lymphocyte has a specific antibody on its surface that is capable of recognising a specific antigen
When antigens are presented to B cells (and TH cells) by macrophages, only the B cell with the appropriate antibody will become activated and clone
The majority of B cell clones will differentiate into antibody-producing plasma cells, a minority will become memory B cells (BM cells)
Because pathogens may contain several antigenic determinants, several B cell clones may become activated (polyclonal activation)
Outline the principle of memory cells (5)
Because the adaptive immune response is dependent on clonal expansion to create sufficiently large amounts of antibodies, there is a delay between initial exposure and the production of antibodies
When a B cell does divide and differentiate into antibody-secreting plasma cells, a small proportion of clones will differentiate into memory cells
Memory cells remain in the body for years (or even a lifetime)
If a second infection with the same antigen occurs, the memory cells react faster and more vigorously than the initial immune response, such that the symptoms of the infection do not normally appear
Because the individual no longer presents with the symptoms of infection upon exposure, the individual is thus said to be immune
Define active immunity
Immunity due to the production of antibodies by the organism itself after the body’s defence mechanisms are stimulated by antigens
Define passive immunity
Immunity due to the acquisition of antibodies from another organism in which active immunity has been stimulated
How can passive immunity be attained? (3)
This passive acquisition of antibodies can be achieved via the placenta, colostrum or by injection (e.g. blood transfusions)
Explain antibody production (7)
Antigens stimulate an immune response via the production of antibodies
When a pathogen invades the body, it is engulfed by wandering macrophages which present the antigenic fragments on its surface
This macrophage becomes an antigen-presenting cell, and presents the antigen to helper T cells (THcells)
The TH cells bind to the antigen and become activated, and in turn activate the B cell with the specific antibody for the antigen
This B cell clones and differentiates into plasma cells and memory cells
The plasma cells produce high quantities of specific antibody to the antigen, whereas memory cells survive in the bloodstream for years
Upon re-exposure to the antigen, memory cells initiate a faster and stronger response and thus confer long-term immunity
Describe the production of monoclonal antibodies and their use in diagnosis and treatment (10)
Monoclonal antibodies (mAb) are antibodies derived from a single B cell clone
An animal (typically a mouse) is injected with an antigen and produces specific plasma cells
The plasma cells are removed and fused (hybridised) with tumor cells capable of endless divisions (immortal cell line)
The resulting hybridoma is capable of synthesising large quantities of specific antigen, for use in diagnosis and treatment
Diagnostic Use:
Monoclonal antibodies can be used to test for pregnancy via the presence of human chorionic gonadotrophin (hCG)
An antibody specific to hCG is made and is tagged to an indicator molecule (e.g. chromatophore or pigment molecule)
When hCG is present in the urine it binds to the anti-hCG monoclonal antibody and this complex will move with the fluid until it reaches a second group of fixed antibodies
When the complex binds to the fixed antibodies, they will appear as a blue line (positive result) due to the presence of the indicator molecule
Treatment Use:
Monoclonal antibodies can be used for the emergency treatment of rabies
Because the rabies virus is potentially fatal in non-vaccinated individuals, injecting purified quantities of antibody is an effective emergency treatment for a very serious viral infection
Explain the principle of vaccination (6)
Vaccinations induce artificial active immunity by stimulating the production of memory cells
A vaccine contains weakened or attenuated forms of the pathogen and is (usually) injected into the bloodstream
Because a modified form of the pathogen is injected, the individual should not develop disease symptoms
The body responds to the vaccine by initiating a primary immune response, resulting in the production of memory cells
When exposed to the actual pathogen, the memory cells trigger a secondary immune response that is much faster and stronger
Vaccines confer long-term immunity, however because memory cells may not survive a life time, booster shots may be required
Discuss the benefits and dangers of vaccination
Benefits:
Vaccination results in active immunity
It can limit the spread of infectious diseases (pandemics / epidemics)
Diseases may be eradicated entirely (e.g. smallpox)
Vaccination programs may reduce the mortality rate of a disease as well as protect vulnerable groups (e.g. youth, elderly)
Vaccinations will decrease the crippling effects of certain diseases (e.g. polio)
It will decrease health care costs associated with treating disease conditions
Risks:
Vaccinated individuals may produce (mild) symptoms of the disease
There may be human error in the preparation, storage or administration of the vaccine
Individuals may react badly to vaccines (e.g. hypersensitive / allergic reactions)
Immunity may not be life long - booster shots may be required
There may be possible toxic effects of mercury-based preservatives used in vaccines
