The Immune System

By: Harshita Dandu and Jenna Song, 1st Period

Innate Immunity

Definition: The body's earliest line of defense against any and all pathogens.


Skin and body secretions:

  • Intact skin is a formidable physical barrier to entrance of microorganisms.
  • Pathogens encounter body's secretion of mucus, oil, sweat, tears, and saliva.
  • Function of mucus: To prevent various parts of the body.
  • Mucus is thick and it traps microorganisms.
  • Sweat, tears, and saliva contain the enzyme lysozyme.
  • Enzyme lysozyme is capable of breaking down the cell walls of some bacteria.

Inflammation of body tissues:
  • If bacteria or other pathogens enter and damage body tissues, inflammation results.
  • Inflammation symptoms: redness, swelling, heat, etc.
  • Inflammation begins when damaged tissue cells called mast cells and white blood cells called basophils release histamine.
  • Histamine causes blood vessels in the injured area to dilate, which makes them more permeable to tissue fluid.
  • Fluid that leaks from the vessel into the injured tissue helps the body destroy toxin agents and restore homeostasis.
  • Inflammation can occur as a reaction to other types of injury as well as infections.

Phagocytosis of pathogens:

  • Pathogens that enter the body may encounter cells that carry on phagocytosis.
  • Phagocytes are white blood cells that destroy pathogens by surrounding and engulfing them.
  • Phagocytes include monocytes.
  • Macrophages are white blood cells that provide the first defense against pathogens that have managed to enter the tissues.
  • Macrophages are found in the tissues of the body.
  • Macrophages are sometimes called big scavengers.
  • Lysosomal enzymes inside the macrophage digest the particles it had engulfed.
  • If the infection is not stopped by tissue macrophages , another type of phagocyte, called a neutrophil comes to the site.
  • If the infection is not stopped by tissue macrophages and neutrophil, a third defense comes in.
  • Monocytes are small immature macrophages that circulate in the blood stream.
  • Once they reach the infected site they mature and are then called macrophages.
  • Pus formation usually continues until the infection subsides.
Protective proteins:

  • Phagocytes alone cannot destroy viruses.
  • A phagocytes that engulfs a virus will itself be destroyed if the virus multiplies within it.
  • Interferons are proteins that protect cells from viruses.
  • Interferons are host-cell specific.
  • Interferons are produced by a body cell that has been infected by the virus.

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Acquired Immunity

Definition: Defending against a specific pathogen by gradually building up a resistance. (White blood cells are developed to recognize specific foreign substances and inactivates or destroys the pathogen).


Acquired Immune Response: Occurs when the immune system recognizes an antigen and responds to it by producing antibodies against it.


Lymphatic System: This organ system helps the body defends against diseases and maintain homeostasis (keeps body fluids constant). Tissue fluids in body's cells diffuses blood into spaces between the cells and collects in open-ended lymph capillaries. The tissue fluid becomes a lymph when it enters the lymph vessels. Lymph flows towards the heart. The lymph veins form two major lymph ducts that returns the lymph to the bloodstream in the shoulder area.


Glands of the lymphatic system: A lymph node is a small mass of tissue that contains lymphocytes and filters pathogens from the lymph. A lymphocyte is a type of white blood cell that defends the body against foreign substances. Examples: Tonsils provide protection against bacteria that enters the nose and mouth and the spleen destroys bacteria and old red blood cells.


Antibody Immunity

Definition: B cells provide immunity against antigens and pathogens in the body fluids.

  • B cells grow and divide rapidly and produce plasma cells and memory B cells where plasma cells release antibodies.
  • Antibodies are proteins that recognize and bind to antigens.
  • The antibodies are carried in the bloodstream to attack the pathogen.
  • The plasma cells die out and stop producing antibodies.
  • After exposed to a pathogen, millions of memory B cells remain able to produce antibodies for that particular pathogen.
  • Memory B cells reduce the chance that the disease would occur a second time.
  • If it occurs a second time, then a secondary phase would occur where the memory B cells divide rapidly forming new plasma cells. The plasma cells then produce antibodies for the destruction of the particular pathogen.

Antibody Structure:

  • Has two identical antigen-binding sites.
  • The shape of the binding sites is affected by the differences in the amino acids.
  • Shape of binding site allow an antibody to recognize a specific antigen with a shape.
  • An healthy adult produces about 100 million different types of antibodies.

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Cellular Immunity

Process of immunity that uses T cells with antigens on the surface.

T-cells are in lymph nodes and transforms into cytoxic T-cells for a particular antigen, but they do not form antibodies. Cytoxic T cells produce identical clones where they travel to a infection site and releases the enzymes into the pathogens. In negative cases, the immune system overreacts to harmless substances and releases mast cells that releases histamines in large amounts. This creates allergic reactions to particular harmless substances. In other cases, the immune system can misunderstand its cells to a foreign cell, leading to attack on the normal cell (autoimmune disorder).

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Passive and Active Immunity

Active Immunity:

  • Vaccination: Injection of a weakened or mild form of pathogen to produce immunity.
  • Vaccines stimulate immune system to create more plasma cells to produce antibodies.
  • Active Immunity is produced by the body's reaction to a vaccine.
  • Appears after exposure to antigen from the result of a immune response.
  • Develops as a result of natural exposure (fighting an infection) or from deliberate exposure to the antigen (vaccine).


Passive Immunity:

  • Occurs when antibodies are produced by other animals against a pathogen injected into the bloodstream.
  • Passive immunity lasts a short time and the body destroys the foreign antibodies.
  • Can develop through natural exposure (fighting an infection) or from deliberate exposure to the antigen (vaccine).
  • Example: Occurs when antibodies produced by the mother are passed to the fetus during development or through breast milk. Immunity protects a child against infectious diseases for early years.
  • Antibodies are sometimes administered to fight infection or prevent disease.
  • Example: Travelers are given vaccines before leaving home which leads antibodies against tropical diseases.

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AIDS and the Immune System

Disease: Pneumonia and Kaposi's Sarcoma were seen as related to a pathogen identified a retrovirus or Human Immunodeficiency (HIV). HIV leads to the destruction of T-cells of the immune system and leads to Acquired Immune Deficiency Syndrome (AIDS). HIV is transmitted when blood or body fluids of a infected person is passed to someone through direct contact. It can also occur when touching a contaminated object of blood or other body fluids. Examples of transmission: Sexual contact, contaminated intravenous needles, and blood-to-blood contact (transfusions of contaminated blood).


Structure: The HIV virus is two copies of RNA wrapped into proteins and lipid coat. These viruses attach to helper T-cells of the immune system. HIV uses lysogenic and lytic cycle of viruses to immobilize the helper T-cells. People with HIV usually gets leaded to the AIDS. When AIDS progresses, the body's immune system weakens and the body's homeostasis is overly disrupted. Some symptoms of the HIV virus is: swollen lymph nodes, nodes, a loss of appetite, losing weight, fever, rashes, night sweats, and fatigue.

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