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The Immune System. By the end of this class you should understand: The nature and needs of different types of pathogens The major components of our body’s.

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Presentation on theme: "The Immune System. By the end of this class you should understand: The nature and needs of different types of pathogens The major components of our body’s."— Presentation transcript:

1 The Immune System

2 By the end of this class you should understand: The nature and needs of different types of pathogens The major components of our body’s defenses against infection The difference between the two branches of the immune system The process by which the body mounts an immune response to infection

3 The Immune System The immune system is a vast and complex network of cells that protect us from infection by pathogens – A pathogen is anything that can cause illness The immune system is often described in military terms and includes imagery of violence – The essential function of the immune system is to distinguish self from nonself And to destroy the nonself

4 Pathogen A pathogen is anything that creates (generates) illness The two most common pathogens are bacteria and viruses Other pathogens include protozoans, worms, flukes, fungi, toxic chemicals, and inanimate objects such as asbestos fibers – Even a certain protein, called a prion, can cause disease by converting your own proteins to prions!

5 Bacteria Bacteria are free-living organisms – Satisfy all criteria for being alive, including having a metabolism and reproducing Most bacteria are entirely harmless – Die when exposed to oxygen, skin, or other bacteria Our body has colonies of bacteria that grow on our skin and in our guts to keep harmful bacteria out – These are called normal flora and taking antibiotics can harm these colonies and render you more vulnerable to infection!

6 Virus A virus is not alive A virus consists of two parts: a nucleic acid strand that contains the information for making more viruses, and a delivery package of protein Viruses convert target cells into factories for making more viral protein and DNA/RNA

7 Pathogenic Activity Every pathogen has its own reasons for harming the human body – Some bacteria invade cells to hide from the immune system – Many viruses destroy the cells they infect in the process of making more viruses – Some bacteria release toxins that harm our tissues – Many pathogenic bacteria that invade the blood do so to eat our glucose

8 Barrier Method Our body has a number of pathogen barriers to prevent pathogen entry – Skin is impermeable to almost all pathogens – Mucus, saliva, tears and earwax all contain pathogen-killing molecules Most infections begin either with breaking the skin or eating/inhaling pathogens that infect the epithelium of the throat or digestive tract

9 Lymphatic Circulation Much like the shoulder of the roads that only police and construction may drive on, our blood has a parallel circulatory system called lymph Lymph is blood plasma and white blood cells, and also picks up pathogens from the tissues Lymph filters through lymph nodes which are packed with white blood cells

10 Immune Tissue Immune tissue is tissue filled with different kinds of white blood cells – Lymph nodes filter the lymph – The spleen filters the blood – Other organs (appendix, tonsils, etc) filter other regions Note these organs can be removed, they are not vestigial but instead are redundant

11 Innate Immune System The innate immune system is one of the two branches of the immune system It is always active It targets anything that doesn’t belong in the body It is not sufficient to repel a major infection – Often compared to police officers (vs. national guard of the acquired immune system)

12 Innate Immune Components Natural Killer cells – Destroy malformed cells such as cancer cells and cells infected with certain viruses Phagocytes – A number of types of cells perform phagocytosis, which means “cell eating” – The two major phagocytes are neutrophils and macrophages Complement – Blood proteins that are toxic to bacteria

13 Phagocytosis Phagocytosis is a three- step process: 1.Detect that something is foreign (e.g. has bacterial cell wall) 2.Engulf that thing into a vesicle 3.Merge that vesicle with a lysosome (vesicle containing lysis enzymes)

14 Neutrophils Neutrophils are the most common white blood cell in the body They perform phagocytosis until they die – Large numbers of dead neutrophils form pus They live primarily in the bloodstream They can access tissues when the tissue is damaged and undergoes inflammation

15 Inflammation When tissue is damaged, histamines are released that signal the local capillaries to dilate, causing them to become leaky Additional blood flows to the larger capillaries – Four signs of inflammation: calor dolor rubor tumor – Heat, pain, redness, swelling – Aids healing and allows neutrophils to enter tissues

16 Inflammation Neutrophils are drawn to the inflammation by the histamines Complement proteins can also leak into the tissues and attach to bacteria Macrophages are large phagocytes that live in tissues – Macrophages can also perform antigen presentation

17 Antigen Presentation An antigen is a molecule from a pathogen that the immune system can respond to Antigen presentation is how the acquired immune system is activated When a macrophage ingests a pathogen it extracts markers from the pathogen and places them in a molecule called MHC2

18 Antigen Presentation A macrophage can migrate through the lymph to lymph nodes and present its MHC2 molecules to Helper T Cells – T cells are trained in a gland called the thymus – Helper T Cells are also sometimes called CD4+ cells because they express the CD4 receptor A Helper T Cell that recognizes the antigen will “activate” by cloning itself and releasing signal molecules

19 Helper T Cell activity Helper T Cells are in control of the other two types of lymphocytes: Killer T Cells and B Cells Helper T Cells are crucial for this activation – The HIV which causes AIDS infects Helper T Cells, preventing the acquired immune system from activating Depending on the type of infection, one or both of the other lymphocytes will be stimulated

20 Killer T Cells Killer T Cells are also known as cytotoxic T cells or CD8+ cells Killer T cells bind to MHC1 molecules found on all cells with a nucleus in the body – MHC1 is an antigen presenting molecule that collects antigens from inside the cell Any cell infected with hidden bacteria or viruses are revealed by the MHC1 and the cell is killed by the Killer T Cell

21 B Cells B Cells, when stimulated by the antigen presentation and Helper T Cell signals, clone themselves and begin producing massive amounts of antibodies – Antibodies stick to the antigen in the blood and tissues and cause them to stick together – Antibodies are also found in saliva, tears, etc

22 Flow of Information

23 Memory Cells When T and B cells are activated and make thousands of clones, some of them become memory cells Memory cells live for decades, constantly searching for the same antigen that activated them in the first place – This is why you normally only get a disease once

24 Vaccination It was noticed in the 19 th century that milk maids never got smallpox because they often got cowpox – Cowpox and smallpox share the same antigens Giving doses of cowpox made it so the subject would not get smallpox and became immune – This was derided as “encowment”, which in french is vaccination

25 Protip: VACCINES DO NOT CAUSE AUTISM There was a time when vaccines were packaged with an antiseptic called thimerosal, which is a mercury- containing compound – They are no longer packaged as such The original study linking vaccines and autism was discredited, and many scientists have repeated the experiment but found no statistically significant difference Autism is a developmental disorder and more prevalent in males, it cannot be caused by an injection at six months of age

26 Thanks for coming! Wednesday: Chapter 13!


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