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Chapter 24: Immune System - Coggle Diagram

- - - - Immune system, the body’s system of defenses against agents that cause disease.
        
        The immune systems of all animals include innate immunity, a set of defenses that are active immediately upon infection and are the same whether or not the pathogen has been encountered previously.
    - - Neutrophils, the most abundant type of white blood cell, circulate in the blood and enter tissues at sites of infection.
        
        Macrophages are large phagocytes that wander through the interstitial fluid, “eating” any bacteria and viruses they encounter.
  - - - In other words, you experience an inflammatory response, a major component of our innate immunity. Any damage to tissue, whether caused by insect bites, microorganisms, or physical injury, triggers this response.
        
        The main function of the inflammatory response is to disinfect and clean injured tissues.
    - - ➊ The bacteria activate macrophages, which produce signaling molecules that increase local blood flow. At the injury site, mast cells (white blood cells that reside in connective tissue) release histamine.
        
        ➋ Induces neighboring blood capillaries to dilate and become leaky. Fluid passes out of the leaky capillaries into the affected tissues. Clotting proteins present in blood plasma pass into the interstitial fluid.
        
        ➌ The neutrophils that migrate into the area engulf bacteria and the remains of any body cells killed by them or by the physical injury. Many of the neutrophils die in the process (or simply come to the end of their short life span), and their remains are also engulfed and digested.
- - - - Any molecule that elicits an adaptive immune response is called an antigen. Antigens are nonself molecules that protrude from pathogens or other particles, such as viruses, bacteria, mold spores, pollen, house dust, or the cell surfaces of transplanted organs.
        
        Antigens may also be substances released into the extracellular fluid, such as toxins secreted by bacteria.
        
        An antibody is an immune protein found in blood plasma that attaches to one particular kind of antigen and helps counter its effects.
    - - Lymphocytes are the white blood cells responsible for adaptive immunity.
    - - It is also possible to acquire passive immunity by receiving premade antibodies.
        
        For example, a fetus obtains its mother’s antibodies through the placenta; after birth, breast milk supplies the baby with antibodies. The effects of a poisonous snakebite may be counteracted by injecting the victim with antivenom, which consists of antibodies extracted from animals previously immunized against the venom. Passive immunity is temporary because the recipient’s immune system is not stimulated by antigens. Immunity lasts only as long as the antibodies do; after a few weeks or months, these proteins break down and are recycled by the body.
  - - - It consists of a branching network of vessels, numerous lymph nodes little round organs packed with macrophages and lymphocytes the bone marrow, and several organs.
        
        The lymphatic vessels carry a fluid called lymph, which is similar to the interstitial fluid that surrounds body cells but contains less oxygen and fewer nutrients.
  - - - Some of these cells, called effector cells, act immediately to combat infection, while others known as memory cells lie in wait, ready to help activate the immune system upon subsequent exposure to the antigen.
  - - - The tip of each arm of the Y forms an antigen-binding site, a region of the molecule responsible for the antibody’s recognition-and-binding function.
  - - - A type of T cell called a helper T cell triggers both the humoral and cell-mediated immune responses. Helper T cells themselves do not carry out those responses. Instead, signals from helper T cells initiate the production of antibodies that neutralize pathogens and activate the cytotoxic T cells that kill infected cells.
        
        The role of helper T cells is so central to immunity that without functional helper T cells, there is virtually no immune response.
    - - First, there must be a foreign molecule that can bind specifically to the antigen receptor of the T cell.
      - Second, this antigen must be displayed on the surface of an antigen-presenting cell. Macrophages and B cells are two types of antigen-presenting cells.
    - - ➊ First, they stimulate clonal selection of the helper T cell, producing both memory cells and additional effector helper T cells.
      - ➋Second, the signaling molecules help activate B cells, thus stimulating the humoral immune response.
      - ➌Third, the signals stimulate the activity of cytotoxic T cells of the cell-mediated immune response, our next topic.
  - - - ➊A cytotoxic T cell with a matching receptor binds to an infected body cell. The T cell then synthesizes several toxic proteins that act on the bound cell, including one called perforin.
      - ➋ Perforin is discharged from the T cell and attaches to the infected cell’s plasma membrane, forming pores in it. T cell enzymes, which enter the infected cell by endocytosis, break down proteins.
      - ➌ The breakdown of proteins kills the infected cell. The death of the infected cell deprives the pathogen of a place to multiply and also exposes the contents of the infected cell to circulating antibodies, which mark the released antigens for disposal.
      - ➍ The cytotoxic T cell may move on to destroy other cells infected with the same pathogen.
  - - - If a virus strain becomes resistant to one drug, it may be defeated by another drug, so patients are typically given multidrug regimens. Unfortunately, some HIV strains have already evolved resistance to multidrug regimens.
    - - . The resistant virus may mutate during this waiting period, causing it to become susceptible to the drugs again. The battle continues, with medical science on one side and the constantly evolving HIV on the other.
  - - - The immune system’s ability to recognize foreign antigens does not always work in our favor. When a person receives an organ transplant or tissue graft, the person’s T cells recognize the MHC markers on the donor’s cells as foreign.
    - - Otherwise, identical twins provide the closest match, followed by nonidentical siblings.
        
        In addition, doctors use drugs to suppress the immune response against the transplant. Unfortunately, these drugs may also reduce the ability to fight infections and cancer.
- - - - In the autoimmune disorder called systemic lupus erythematosus (lupus), B cells produce antibodies against a wide range of self molecules, such as histones and DNA released by the normal breakdown of body cells.
        
        Lupus is characterized by skin rashes, fever, arthritis, and kidney malfunction.
      - Rheumatoid arthritis is another antibody-mediated autoimmune disorder, in which the immune system attacks synovium, a thin layer of tissue that lines joints.
        
        Symptoms of rheumatoid arthritis include damage to and painful inflammation of the cartilage and bone of joints.
    - - Immunodeficiency may be acquired later in life, as in the case of AIDS. Another example of an acquired immunodeficiency is Hodgkin’s disease, a type of cancer that damages the lymphatic system and can depress the immune system.
  - - - Later exposure to the same allergen
        
        ➍ The allergen enters the body and binds to the antibodies attached to mast cells.
        
        ➎ This causes the mast cells to release histamine, which causes blood vessels to dilate and leak fluid, leading to nasal irritation, itchy skin, and tears.
      - Sensitization: Initial exposure to an allergen
        
        ➊ After an allergen enters the bloodstream, it binds to effector B cells with receptors specific to the allergen.
        
        ➋ The B cells then proliferate through clonal selection and secrete large amounts of antibodies to this allergen.
        
        ➌ Some of these antibodies attach to the surfaces of mast cells that produce histamine and other chemicals, which trigger the inflammatory response.