11.1 Defence Against Infectious Disease Flashcards
Describe the process of blood clotting
- 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
State the functions of blood clotting
To prevent further loss of blood from broken vessels and to block entry to foreign pathogens
Outline the principle of challenge and response
Immunity to a specific pathogen is only developed once the body is challenged by that pathogen
• When challenged, the body responds with both a specific and non-specific immune reaction
• Non-specific immune cells (macrophages) engulf the pathogen, incorporate its antigens into its membrane, and present the antigens to lymphocytes (non-specific response)
• These lymphocytes can then produce antibodies to specifically target the pathogen (specific response)
Outline the principle of clonal selection
Macrophages must present antigens to the appropriate, specific B cell (lymphocyte) so that it can begin to clone itself into plasma and memory cells, and produce the needed antibodies
• Each B cells has a specific antigen receptor on its surface which is capable of recognising a specific antigen
• When macrophages present antigens to lymphocytes, only the specific B cell will activate and clone, meaning only the needed antibodies are produced
• The majority of B cell clones will differentiate into antibody-producing plasma cells, while the minority will become memory cells
• Because pathogens may contain several antigenic determinants, several B cells may become activated by a single pathogen (polyclonal activation)
Outline the principle of memory cells
Allow the body to have long term specific immunity against the pathogen, even after B-cells and antibodies are gone
• Memory cells remain in the body for years (or even a lifetime)
• If a second infection of the same antigen occurs, the memory cells react faster and more vigorously than the initial response, such that the symptoms of the infection do not normally appear
• Because the individual does not present symptoms of infection upon exposure, they are 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
• Can be achieved via placenta, colostrum (early breast milk), or vaccination
Define innate immunity
Immunity from birth due to genetic factors
Explain antibody production (HL)
- Pathogen enters body
- Pathogen engulfed by macrophage, which presents pathogen’s antigens on its surface
- Macrophage binds to and activates helper T cell
- Helper T cell activates B cells
- B cell clones, differentiating into plasma cells and memory cells
- Plasma cells secrete large amounts of antibodies
- Memory cells remain in body and provide long term specific immunity
Describe production of monoclonal antibodies
- Monoclonal antibodies 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 tumour cells capable of endless divisions (immortal cell line)
- The resulting hybridoma is capable of synthesising large quantities of specific antigen as it continues to divide and grow
- Antibodies can then be extracted and purified for use in diagnosis and treatment
Describe a diagnostic use for monoclonal antibodies
Can be used to test for malaria
• The monoclonal antibodies can bind to the malaria antigens
• A blood sample is taken and placed on a test plate covered in antibodies
• An enzyme is added which causes the plate to change colour in the presence of antibodies bound to antigens
Describe how monoclonal antibodies can be used for treatment
Can treat anthrax
• Anthrax bacteria secrete poisons, and monoclonal antibodies can be injected to neutralise the toxins until the body has time to respond and produce its own antibodies
Explain the principle of vaccination
Vaccinations induce artificial specific immunity by triggering the production of memory cells
• A vaccine contains a dead or weakened form of the pathogen and is (usually) injected
• The modified version of the pathogen does not cause the individual to develop disease symptoms
• The body responds to the vaccine, 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 of vacination
- Protection for the individual from an infection and its harmful effects
- Protection for a community through herd immunity
- Diseases can be eradicated entirely (smallpox)
- Can limit the spread of infectious diseases, preventing epidemics
- Reduced economic burden of healthcare for the sick
Discuss the dangers of vaccination
- Vaccinated individuals may show mild symptoms of the disease
* Individuals may present allergic/hypersensitive reactions- Possible toxic side-effects of mercury-based preservatives used in vaccines
