The Immune System (ch. 43)
  • Innate Immunity:
    • Rapid response of the immune system
    • Recognizes traits that generally are in pathogens, using receptors.
    • Innate immune system contains two sub parts: Barrier Defenses and Internal Defenses
      • Barrier defenses: Skin, Mucous membranes, Secretions, etc.
      • Internal Defenses: Phagocytic cells, Natural Killer cells*, Antimicrobial proteins*, Inflammatory response*, etc.
        • Phagocytosis:
  • Natural Killer Cells
  • Inflammatory response


*only occurs in vertebrates
  • Adaptive Immunity:
    • Slow response of the immune system
    • Recognizes specific traits of specific pathogens, using a large amount of different receptors
    • Adaptive Immune System has two sub parts: Humoral response and Cell-mediated response
      • Humoral Response: Antibodies (B and T cells) defend against infection in body fluids(plasma, lymphatic fluid, etc.) using antibodies to neutralize the antigens
      • Cell-mediated Response: Cytotoxic cells defend against infection in body cells.

  • Innate immunity in invertebrates vs. vertebrates
    • the barriers for vertebrates are generally more effective at blocking pathogens than the barriers of invertebrates
    • Utilizes Phagocytic cells, Natural killer cells, the Inflammatory response, and many more
    • the barriers in vertebrates include not only skin, but also mucous covered membranes that are in reproductive, digestive, respiratory, and urinary tracts.
    • The cellular innate defenses in vertebrates include TLR's (Toll-like receptor), Neutrophils, macrophages, dendritic cells, natural killer cells, and interferons.
      • TLR's
        • They recognize certain pathogens, and attach to them, so they can be "eaten" by Phagocytic cells
        • Look at figure 43.6 in textbook for diagram representation of TLR signaling
      • Neutrophils
        • They are the most abundant type of white blood cell
        • They are phagocytic, and they tend to die when they "eat" unknown materials, (they may not be pathogens, but if it does not recognize it, it will "eat" it), so their life span is usually only a few days.
      • Macrophages
        • macro=big, phage=eat ----> macrophage = big eater
        • Macrophages are a type of white blood cell.
        • Macrophages are Phagocytic, but unlike Neutrophils, they do not die after "eating" an unknown material.
      • Dendritic Cells
        • they are an antigen-presenting cell, mainly found in lymphatic tissues and the skin that are particularly efficient when it comes to presenting antigens to the helper T cells.
        • By presenting it to the Helper T cells very efficiently, this initiates a primary immune response.
      • Natural Killer Cells
        • They are cells that can kill tumor cells and cells that are infected with a virus.
      • Interferons
        • They are proteins that have antiviral or immune regulatory functions.
        • Interferon-alpha or Interferon-beta, are secreted by virus-infected cells, they help cells that are near not get infected.
        • Interferon-gamma is secreted by T cells, and they help with the activation of macrophages.
    • vertebrates also have an inflammatory response, which invertebrates do not.
      • When the skin is punctured, mast cells and macrophages are nearby, releasing signaling molecules, one of the most important signaling molecule is histamine.
      • Neutrophils then go to the site of puncture and phagocyte any unfamiliar material that may have entered the body via the puncture site.

  • Adaptive immunity in vertebrates: development and function of antigen receptor cells
    • lymphocytes
      • lymphocytes are very important for adaptive immunity
      • They are a type of white blood cell that mediate immune responses
      • There are two types of lymphocytes: B cells and T cells
        • B Cells
          • These are lymphocytes that mature in bone marrow and then become effector cells for the humoral immune response.
        • T cells
          • They are lymphocytes that mature in the thymus(small organ in thoracic cavity of vertebrates)
          • They include both effector cells for the cell-mediated immune response, and helper cells required for both branches of adaptive immunity, Humoral and Cell-mediated
    • Antigen
      • anything that educes a response from a B cell or T cell.
      • B and T cells have Antigen receptors, which bind to antigens, and initiate adaptive immune responses
        • The place where the B and T cells bind to the antigens is called the epitope
      • Antibody
        • A protein that is secreted by plasma cells, that bind to specific antigens.
        • They are also known as Immunoglobin
        • All anti bodies have Y-shaped structure and in their monomer form consist of two identical heavy chains and two identical light chains.
  • Effector Cells: A lymphocyte that has undergone clonal selection and is capable of mediating an adaptive immune response
  • Memory Cells: One of a clone of a long-lived lymphocytes, formed during the primary immune response, that remains in a lymphoid organ until activated by exposure to the same antigen that triggered its formation. activated memory cells mount the secondary immune response
  • Primary immune response: the initial adaptive immune response to an antigen, which appears after a lag of about 10 to 17 days
  • Secondary immune response: The adaptive immune response educed on second or subsequent exposures to a particular antigen. It is longer, greater in magnitude, and takes longer time than the primary immune response.
  • Helper T cells: A type of T cell that, when active, will secrete cytokines that promote the response of B cells and Cytotoxic T cells to antigens.
  • Cytotoxic T cells: A type of lymphocyte that, when active, will kill infected cells and certain cancer cells and transplanted cells.
  • The following figure is an overview of the adaptive immune response (figure 43.20 from textbook)

  • Immunization: active vs. passive
    • An immunization is the process of generating a state of immunity to a certain pathogen, using artificial means.
      • Active Immunization (vaccination)
        • A vaccination is when a weakened or inactive form of a pathogen is given, and this induces B and T cell responses, and immunological memory.
          • Example: MMR vaccination
      • Passive Immunization
        • antibodies specific for a particular pathogen are given, this activates immediate protection, but this protection is also temporary.
          • Example: Tetanus shot, Rabies shot, Hepatitis B shot

  • Transplantation and immune rejection
    • transplantation is when a body part/body fluid is transferred into an organism
      • For transplants to work, the organ needs to come from the same organism, that organism also needed to have a blood type that would conform to the transplantee's blood type. For example, someone who is blood type O negative, they can only get organs from other person who had blood type O negative, while blood type AB positive can get a transplant from any blood type.
    • Immune rejection
      • cells from another person are considered foreign cells to the cells in a persons body. The cells may attack the foreign cells, even if they are transplanted cells. This is expected because these cells are foreign, and the immune system is designed to reject foreign cells
        • An unanswered question is why a pregnant woman does not reject her fetus as no her own tissue.
      • Blood groups
        • Blood transfusions need to be done very carefully. Only some blood types can be mixed with others. This table should be helpful

Blood type
What blood types can receive this type
What blood types this type can receive
O+, A+, B+, AB+
O+, O-
all blood types
A+, AB+
A+, A-, O+, O-
A+, A-, AB+, AB-
A-, O-
B+, AB+
B+, B-, O+, O-
B+, B-, AB+, AB-
B-, O-
all blood types
AB+, AB-
AB-, A-, B-, O-
      • Tissue and Organ transplants
        • MHC molecules are molecules that stimulate immune response that leads to rejection of cells. No ones MHC molecules are the same, except for identical twins
        • What doctors do is that they find the closest match for MHC molecules between the donor and the receiver of the organ/tissue.
        • Hospitals need great variability of donors for a great variability of MHC.
  • Exaggerated, self-directed, and diminished immune responses (allergies, autoimmune, and immunodeficiency diseases)
    • Allergies
      • Allergies are exaggerated responses to certain antigens called allergens. (Not all organisms have allergies)
      • Allergies usually involve antibodies of the IgE
        • An example of an allergy is Hay Fever. Hay Fever is when plasma cells secrete IgE antibodies specific for antigens on the surface of pollen grain.
      • Allergies often cause the release of a hormone called histamine
      • Many allergies can be reduced by taking an antihistamine.

    • Autoimmune diseases
      • An autoimmune disease is a disease that causes the immune system to attack its own cells.
        • Example: lupus
          • Lupus is a disease where the immune system creates antibodies and against histones and DNA released by normal breakdown of body cells. This causes rashes, kidney dysfunction, arthritis, fever, and possibly many more symptoms.
        • More examples of autoimmune diseases: rheumatoid arthritis, type 1 diabetes, multiple sclerosis.
      • Women are 2 to 3 times more likely to develop rheumatoid arthritis or multiple sclerosis, and 9 times more likely to develop lupus than males.
    • Immune system and moderate exercise
      • Moderate exercise can improve the function of your immune system.
      • Exercise to the point of exhaustion does not improve immune system.
        • A study was done and shown that marathon runners did not get sick during training.
    • Immunodeficiency diseases
      • Immunodeficiency is when the immune system is unable to protect against pathogens, meaning the ability is either absent or defective.
        • Inborn immunodeficiency is developed when the immunodeficiency is a genetic or developmental defect in the immune system
          • example: Severe Combined Immunodeficiency (SCID)
        • acquired immunodeficiency is developed later in life due to exposure to chemical or biological agents.
          • example: Acquired immunodeficiency syndrome (AIDS)
  • Antigenic variation
    • Antigenic variation is when an antigen can change forms, causing a longer time for the immune system to recognize it,
      • example: Trypanosomiasis (sleeping sickness)
    • Flu outbreak
      • the Influenza outbreak in 1918-1919 lasted so long because their were so many forms that the disease was changing to. This outbreak cause more deaths than World War I.
    • H1N1
      • H1N1 became a pandemic in 2009 because of its antigenic variation. Luckily, we were able to quickly develop a vaccine.
  • Latency
    • Latency is when a virus in a host enter a state of inactivity
  • HIV, cancer, and immunity
    • Human Immunodeficiency Virus (HIV)
      • Causes AIDS
      • HIV does both escape and attack the adaptive immune response.
      • It highly efficiently infects Helper T cells, and eventually the virus DNA is integrated into the human's genome
      • The Immune system does try to stop the HIV< but some of the HIV does escape
      • The HIV evolves with the human body, and this is helped by latency, as seen in figure 43.25 below.

    • Cancer and Immunity
      • When adaptive immunity is inactive, the frequency of cancer is dramatically increased
        • example: People with AIDS are 20,000 times more likely to get Kaposi's sarcoma than healthy people.
      • It has been found out that 15-20% of cancer is caused by a virus.
      • This means an immune system can help defend against cancer, because the immune system will attack foreign cells.
      • Scientists have identified 6 types of viruses that can cause cancer, two of them being Kaposi's sarcoma herpesvirus and Hepatitis B.
        • In 1986, a vaccine was created for Hepatitis B, which became the first vaccine that could prevent a human cancer.
        • Human papillomavirus (HPV) causes cervical cancer, and in 2006, a vaccine for HPV was released, and over 500,000 women are afflicted every year by this.