Defence Against Infectious Disease Flashcards
Explain why antibiotics are effective against bacteria but not viruses
Antibiotics block specific metabolic pathways found in bacteria. Viruses reproduce using host cell’s metabolic pathways which aren’t affected by antibiotics.
Define pathogen
Organism or virus that causes a disease
Outline the role of skin and mucous membranes in defence against pathogens
Skin
- physical barrier (tough and difficult to penetrate)
- natural microbes inhibit (competitive) growth of pathogenic microbes
- sebaceous glands secrete chemicals to make skin acidic
- tears/saliva wash bacteria away
Membranes
- line respiratory, urinary, reproductive, gastrointestinal tracts
- contain lysozyme (destroys bacteria)
- in respiratory, sticky mucous catches pathogens which are pushed by cilia out the trachea
Distinguish between antigens and antibodies
Antibodies - proteins secreted by plasma B cells which recognize/bind to specific regions of pathogens/antigens
Antigens - foreign molecules that elicit specific immune response by lymphocytes
Outline how phagocytic leukocytes ingest pathogens in the blood and in body tissues
WBC count increases 2-4 times; phagocytes migrate into tissues.
- Detection - phagocyte detects microbes by chemicals they give off (chemotaxis)
- Ingestion - endocytosis of microbe by pseudopods
- Phagosome forms - phagocytic vesicle encloses microbe in membrane
- Fusion with lysosome - lysosome contain enzymes to digest microbe
- Digestion - microbes are broken down
- Discharge - exocytosis
Explain antibody production
Many different types of lymphocyte exist. Each type recognizes one specific antigen and responds by dividing to form a clone. This clone then secretes a specific antibody against the antigen.
B cells produce antibodies, macrophages and helper T cells activate them.
1. Antigen presentation - macrophages endocytosis the antigens and present them on MHC proteins through exocytosis
2. Activation of helper T cells - inactive Th cell binds to macrophage which sends signal (interleukin) to active it
3. Activation of B cells - antigen on Th cell binds to antibody on inactive B cell; Th cell sends signal (interleukin) to activate
4. Production of plasma cells - B cells divide (mitosis) to form clones (plasma cells); contain rER to synthesize antibody
5. Production of memory cells - last 20+ years; allow secondary immune response
Outline the effects of HIV on the immune system
- reduction in the number of active lymphocytes
- loss of the ability to produce antibodies
Discuss the cause, transmission and social implications of AIDS
Cause: HIV (retrovirus) contains RNA and uses helper T cells as a host; infected die from other diseases
Transmission: transfer of body fluids through sex, needles, childbirth, blood
Social Implications: grief of family, reduced workforce, discrimination, increased cost of health care, decrease in sex
Describe the process of blood clotting
- Blood vessel tears which releases clotting factors (platelets, damaged cells, plasma)
- Platelets adhere to form plug
- Fibrin clot with trapped cells (insoluble)
Plasma -> Prothrombin (inactive) -> Thrombin (active) catalyzes Fibrinogen (soluble) -> Fibrin
Define active immunity and passive immunity
Active immunity - immunity from production of antibodies after body’s defence mechanisms have been stimulated by antigens
Passive immunity - immunity from acquiring antibodies from another organism so active immunity has been stimulated, including via the placenta, colostrum, or injection of antibodies
Outline the principle of challenge and response, clonal selection and memory cells as the basis of immunity
Principle of Challenge and Response: Immunity is only developed if immune system is activated (challenged) by pathogen and response is elicited
Clonal Selection: Antigen-driven cloning of B cells where antigen selects B cells that will proliferate
Memory Cells: B cells differentiate into plasma and memory cells (retained in lymph node so secondary response can occur)
Polyclonal Selection: Multiple types of antibody bind to same antigen so more than one clone produced
- infectious diseases, cancers, transplant rejections
- small quantities of different types of B cells are generated during lymphocyte development
• capable of producing antibodies for different antigens (even un-encountered antigens)
• has specific type of antigenic receptor
- B cell binds to antigen and divides by mitosis to form clone cells that produce antibodies
Describe the production of monoclonal antibodies and their use in diagnosis and in treatment
Production:
- Large quantity of one type of pure antibody used in medical research/treatments
1. antigens (eg. cancer) injected into mouse
2. B plasma cells extracted
3. tumour cells obtained
4. in culture, B plasma and tumour cells fuse, producing hybridoma cells
5. hybridoma cells are cultured so antibodies can be extracted/purified
Uses of Monoclonal Antibodies:
a) Treatment
- injections control rabies (temporary), vaccine increases antibodies
- target cancer cells using conjugated monoclonal antibodies with attached drugs
• limited use; could be rejected
• hope to use human cells vs mouse cells
b) Diagnosis (for malaria)
- monoclonal antibodies bind with antigens in malarial parasites (protozoan Plasmodium)
- blood sample from patient is left in antibody-covered plate so antigens can bind to antibodies
- bound antigens are detected using enzymes on monoclonal antibodies that change colour
- ELISA test (Enzyme-Linked ImmunoSorbent Assay)
- measure levels of infection; distinguish between strains of malaria
- also used for diagnosis of HIV, herpes virus, heart attack, pregnancy (HCG)
Explain the principle of vaccination
- attenuated (weakened) or killed form of pathogen, or chemicals produced by pathogen
- injected or swallowed
- induce develop of memory B cells
- cause primary exposure and response so subsequent exposure elicits secondary response
Primary Immune Response:
- exposure occurs; causes selective proliferation of B cells
- 10-17 days needed to produce max # of antibodies
- symptoms stop as antibodies/T cells clear antigen; not severe as real disease
Secondary Immune Response:
- production of antibodies is faster (2-7 days), greater, and longer
- antibodies have greater affinity to antigen
- memory cells proliferate and differentiate rapidly the second time; eliminates pathogen before illness
- first response generated from memory cells; also as normal exposure produces activated T cells and plasma B cells
Discuss the benefits and dangers of vaccination
Benefits:
- epidemics/pandemics prevented; some diseases completely wiped out (smallpox, soon polio)
- death/disability prevented
- decreased health costs
Dangers:
- allergic reactions (anaphylaxis) to eggs/antigens
- fever/pain/swelling
- mercury is toxic
- overload of immune system (reduces response to new diseases)
• more afraid of vaccine than disease (eg. MMR vaccine associated with autism)
