PBL Week 3 Flashcards
What are the different organs and cells of the immune system?
Bone marrow develops B cells while the Thymus gland develops T cells. (Primary immune tissues/organs).
Spleen, tonsils, appendix, lymph nodes, adenoids, peyer’s patches and mucosa associated lymphoid tissue (MALT) are where lymphocytes act on pathogens (Secondary immune tissues/organs).
The skin acts as a defensive barrier, while stomach acid, mucous, tears etc act to capturea and/or kill pathogens.
Lymph nodes are placed around the body, dendritic cells carry pathogens from the infected site to the lymph nodes.
Eosinophils, basophils and mast cells (which release histamine) bind to large pathogens and release toxic enzymes. They are also responsible for allergic responses.
Neutrophils and macrophages bind to medium pathogens (bacteria) and break them down with digestive enzymes (phagocytosis).
Natural Killer cells attack the smallest pathogens (viruses) by binding to them and releasing cytotoxic components.
T-lymphocytes bind to a specific antigen. Can be T-helper cells (fights bacteria + fungi) and cytotoxic T-cells (fights cancer + viruses).
B-lymphocytes also bind to specific antigens and, once they do, they become either memory cells (remembers antigens) or plasma cells (secrete antibodies).
Antibodies bind to specific antigens, either signalling phagoycytes or activating the complement system.
How does the immune response work?
The innate immune system is the first line of defense. It’s non-specific, responds in minutes and has no memory. Is made up of the epithelial barriers, which protect the body from infection, as well as phagocytes, dendritic cells and NK cells. Phagocytes bind to medium sized pathogens it comes across, releasing digestive enzymes and breaking them down. NK cells are signalled by invaded cells (e.g tumours, virus-invaded cells) and bind to them, releasing cytotoxic components to kill the cell. Dendritic cells are cells that pick up pathogens at the site of infection, presenting the pathogen’s antigen on their surface.
The adaptive immune system is next. It is specific, slower to respond and has a memory. A dendritic cells moves to a lymphocyte and presents the invading antigen. If a lymphocyte binds to a matching antigen, they activate and rapidly divide. Then, the specific B and T lymphocytes can function; T-helper cells activate B-cells, cytotoxic T-cells and macrophages. Cytotoxic T-cells kills viral-infected cells. B plasma cells create antibodies to fight the infection and B memory cells remain past infection to “remind” the immune system of the pathogen.
What is the difference between active and passive immunity?
Active - body makes antibodies, is specific and has a memory. Can be natural (fighting infection) or artificial (vaccinations).
Passive - antibodies placed into body, is specific but no memory. Can be natural (antibodies in breat milk) or artificial (innoculation).
What are the differences between different types of bacteria?
Bacteria either have a thick peptidoglycan layer and no outer lipid wall and can be stained purple (gram positive) or a thin layer and the presence of an outer lipid wall and can be stained pink (gram negative). Bacteria can also be circular cocci or the rod-shaped bacilli. Some are aerobic and some are anaerobic. Can come in clusters, chains or tiny spores.
What are the different microbiological agents?
Bacteria, Viruses (invade cells and use the cell’s resources to reproduce), Funghi, Protozoa, Prions (proteins), Helminths (parasitic worms) and Ectoparasites (e.g lice).
What are the different signs and symptoms of infection and how do they come about?
Tissue damage can have 5 symptoms - dolor (pain), calor (heat), rubor (redness), tumor (swelling) and functio laesa (loss of function). These symptoms are usually due to the increased blood supply and the migration of immune cells to the site.
Microbes cause symptoms such as fever, swollen glands and rashes not because of the microbes themselves, but due to our immune response. However, this isn’t always the case; endotoxins produced by bacteria excacerbate the immune response and exotoxins negatively affect our cells.
High lympocytes normally are a sign of a viral infection. High neutrophils are a sign of a bacterial infection.
How are laboratory investigations involved with the diagnosis of infectious diseases carried out and what are their shortcomings?
First, a medical history and clinical examination is taken. The doctor will then develop a diagnosis and take a clinical sample from the patient for testing. In the case of bacteria, this test will most likely be a gram stain, which is used to determine if a bacteria is gram postive or negative. It is performed on a smear sample (thin layer of bacteria on a slide).
First, chrystal violet is added to the sample, then water is applied to wash off the dye, with both types of bacteria now purple. Then, gram’s iodine is added and again washed off with water. Next, drops of alcohol or acetone is added until the drops running off the slide are colourless. This removes the violet dye from the gram negative only. Finally, safranin is added and is again washed off with water. This should make the gram negative pink and the gram positive should remain purple. The downside to this is that some pathgoens are missed by this test.
Alternatives include culturing the pathogen, however this can take weeks and not all pathogens can be cultured. Microscopy can also be done, but the accuracy of diagnosing the pathogen depends on the microscope used and the experience of the microscopist.
What are the key principles behind infectious disease control?
Prevention, preparation, detection, protection, response, control and elmination.
What is the role of antibiotics in treating infectious diseases?
Antiobiotics are a type of drug that targets bacteria - it has no effect on other pathogens. They work by targeting the bacterial cell wall, bacteria’s protein synthesis, their nucleic acid synthesis and the bacterial membrane.
However, bacteria can resist antibiotic effects by reducing permeability (antibiotic isn’t taken into cell), increased efflux (antibiotic is expelled quicker), target modification (the molecular strucutre of the binding site is altered so the antibiotic cannot bind) and inactivation (alter the antibiotic so that it degrades and cannot function).
Furthermore, some bacteria are becoming resistant to some and even all antibiotics due to increased exposure. Therefore, antibiotics must be used conservatively.
How have treatment options for bacterial infections changed over the last 150 years?
Joseph Lister focused more on prevention of bacterial infections rather than treatment. In 1965, he became one of the pioneers of aseptic surgery by cleaning wounds and surgical tools in carbonic acid, vastly reducing cases of bacterial infections.
Paul Ehrlich was interested in dyes that could both stain and kill bacteria, which he dubbed “magic bullets”. He only found one; in 1909, he found that Salvarsan was effective against Syphillis, but unfortunately was also toxic and had many side effects.
Gerhard Domagk carried on Ehrlich’s work and discovered Prontosil in 1939, which was effective against streptococcus and staphylococcus infections.
Jorgen Lehmann modified aspirin into para-amino salicyclic acid (PAS) in the 1940s, creating an effective treatment for TB.
In the 1920s and 1930s, bacteriophages were used as a treatment for bacterial infections. They are specific viruses that bind to their respective bacteria’s antigens. However, they were overshadowed by antibiotics due to their specificity and difficulty to produce.
In 1929, Alexander Fleming accidentally discovered Penicillin, a fungus with anti-bacterial properties. While he couldn’t find a way to use it effectively, Howard Florey and Ernst Chain were the first to create an effective way to grow and develop a treatment from penicillin in the early 1940s. Since then, many antibiotics have been found, although few have been discovered since the 1970s.
How has the understanding of the causes and cures of infectious disease changed over time?
Ancient times - Caused by evil spirits/trepanning.
Ancient Greeks (Hippocrates) - 4 humours
Middle Ages - astronomy, religious reasons
Renaissance - bacteria discovered but not thought to be important, lots of conflicting ideas. Miasmata theory (bad air) was the most believed.
1950s - Germ theory pioneered by Louis Pasteur.
What are the pros and cons of vaccination?
Pros - protects people from disease, creates herd immunity, are well researched so are most likely safe.
Cons - possible allergic reactions, not 100% effective, ethical considerations (religious reasons, personal reasons, children cannot consent to it themselves etc).
