Immune System

Two Types of Immune Defenses

1) Innate Immunity

  • Nonspecific defense
  • Rapid response to various microbes
  • Surface Barriers:
    • Skin
    • Saliva
    • Tears
    • Stomach acid
  • Inflammation- biological response to harmful stimuli (pathogens, injury)
    • Chemokine- attract white blood cells to inflamed area
    • Neutrophils- first responder to inflammation
    • Phagocytes- engulfs and absorbs microbes
    • Leukocytes- white blood cells
    • Macrophages- large phagocytic cells
    • Fever- due to increase in temperature, which kills bacteria
  • Complement- proteins that enable removal of microbes and damaging of infected cells
  • Natural Killer Cells- release substances that will kill/ pop cell
    • May cause apoptosis (suicide of the cell)
  • Histamines- trigger vasodilation (enlargement of blood vessels), increasing blood supply to inflamed area --> more phagocytes --> more microbes killed
  • Interferons- chemicals that fight viral infections

External Defense

  • Skin
  • Tears
  • Mucus
  • Secretions

Internal Defense

  • Phagocytes
  • Natural Killer Cells
  • Inflammation
  • Antimicrobial proteins


2) Adaptive Immunity

  • Specific Defense
  • Slower response to specific microbes
  • More efficient because it produces memory cells
  • 1) Humoral Response
  • 2) Cell-Mediated Response

Humoral Response

  1. Activation of B lymphocytes
  2. Plasma B cells- produce antibodies; activated by a Helper T Cell
    1. Antibodies: identify and remove foreign antigens
      1. Bind to a particular antigen only
        1. Antigen: a foreign substance that triggers an immune response from a B cell or T cell
      2. Structure:
        1. 2 identical heavy chains and 2 identical light chains
        2. Antigen binding site: located at the end of the antibody; binds to a specific antigen
  3. Memory B cells- fight same antigens as plasma B cells
    1. Immunological memory: ability to remember specific viral pathogens to prevent an individual from receiving the same viral infection again

Cell- Mediated Response

  1. Activation of T lymphocytes
    1. T cells destroy infected host cells
    2. T cells mature in an organ called the thymus
    3. 4 Types of T cells:
      1. Helper T cells
      2. Killer T cells
      3. Suppressor T cells
      4. Memory T cells
  2. Helper T cells- triggers Humoral response and Cell-Mediated response
    1. Triggers Plasma B cells to produce antibodies to a specific antigen
  3. Killer T cells- terminate cells infected by a virus or bacteria and cancer cells
  4. Suppressor T cells- release hormones that stop Killer T cells after the immune response has achieved its goal
  5. Memory T cells- remember antigens that the immune system has already encountered to defeat the same antigen in the future


Immune Diseases


  • The Immune System is impaired from defending the body and fighting foreign substances 
  • For example: Human Immunodeficiency Virus (HIV)
    • Virus that causes progressive failure of the immune system, making the body vulnerable to harmful pathogens.
    • HIV is a retrovirus that attacks helper T cells, thus helper T cells can no longer activate plasma B cells to produce antibodies to specific pathogens
    • HIV may lead to acquired immunodeficiency syndrome (AIDS) 
    • AIDS develops when HIV is advanced and the body is too weak to fight off many infections

Auto Immune Disorders

  • An individual's body is too weak to distinguish between "self" and "non-self," and the immune system attacks itself
  • Healthy cells are attacked
  • For example: Multiple Sclerosis
    • Body attacks its own nerve cells

Two Types of Immunity

Active Immunity

  • The body produces its own antibodies
  • Immunity lasts for a long time
  • For example
  1. When an individual is exposed to a pathogen, and the immune system produces antibodies to fight that specific pathogen
  2. When an individual is injected with a weakened form of the pathogen (vaccine) and develops antibodies to the pathogen

Passive Immunity

  • The body does not make its own antibodies
  • Immunity lasts for a short period of time
  • For example:
  1. When an individual receives antibodies from breastfed milk
  2. When an individual is injected with antibodies to fight a specific pathogen

Test Yourself

Which of the following statements is not true?

  • An antibody has one antigen-binding site
  • Neutrophils attract white blood cells to the inflamed area
  • B cells respond the first time a pathogen is present; T cells respond subsequent times
  • Passive immunity provides immediate, long term immunity

True or False

  • Macrophages are specialized proteins that fight disease.

The inflammatory response includes all of the following EXCEPT

  • Engulfing of microbes
  • Vasodilation
  • Production of antibodies
  • Increase in body temperature

True or False

  • HIV is such a deadly disease because AIDS attacks helper T cells.

The immune response is terminated by

  • Suppressor B cells
  • Killer T cells
  • Suppressor T cells
  • none of the above; the immune system cannot be terminated

A vaccination is an example of

  • Naturally acquired passive immunity
  • Artificially acquired active immunity
  • Naturally acquired active immunity
  • Artificially acquired passive immunity