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Immune system

Front-loading vocabulary

The Immune system is a system of cells and chemicals which recognize, target and destroy pathogens.

Pathogens are organisms that cause a disease in another organism.

RBC = red blood cells, which carry oxygen from the lungs to all body tissues.

WBC = white blood cells, which fight pathogens.

How does the immune system target invaders?

All cells have many different proteins on their cell membranes. Each has their own name and job.

antigens on cell membrane

When we learn how they are recognized by our immune system, we don’t care about their names. We just care whether or not they trigger an immune response. These cell membrane proteins are called antigens.


{ image from http://biginscience.com/big-in-science-articles/2013/12/1/cancer-vaccine-extends-life-for-patients-with-the-most-common-aggressive-form-of-brain-cancer }

When our WBCs “eat” a pathogen (like Pac Man), they then display broken bits of the dead pathogen on their surface. This helps other parts of the immune system recognize the pathogen.

from NobelPrize Org phagocyte antigen


{ from http://www.nobelprize.org/educational/medicine/immunity/immune-detail.html }

Killer T cells

  • Helper T cells can stimulate Killer T cells in response to a particular antigen
  • Killer T cells attack infected body cells and kill them
  • They release enzymes directly into pathogens causing them to lyse and die.

Killer T-Cells


{ from http://kmbiology.weebly.com/immune-response—notes.html }

B-cells bind to antigens

  • Then the B-cells are activated by helper T-cells and divide
  • The cloned B-cells can develop into either Plasma Cells or Memory Cells

Plasma Cells

  • Produce antibodies that are released into the blood stream and tissue spaces
  • Antibodies – Y-shaped proteins produced in reaction to antigens that react with and disable antigens
  • Pathogens covered with antibodies are easier to attack and engulf

B Cells bind to the antigens

Our WBCs that “touch” every cell in our body

If they recognize these antigens as “self” (part of you) then they do nothing. If they do not recognize them , then they are “non-self” (not part of you), and therefore targeted for destruction.

What cells would our WBCs not recognize?
* pathogens
* body cells which could become cancerous.
* On super rare occasions, a terrible mistake is made – and WBCs fail to recognize one of our own normal body cells. This could cause an auto-immune disease.

Many types of WBCs

RBC = carry O2 (oxygen gas) from the lungs, to every tissue in our body

RBC = carry CO2 (carbon dioxide gas) from every tissue in our body, back to our lungs, where we exhale it

WBC = White blood cell, job is to kill anything it doesn’t recognize

Phagocytes, like Pac Man, engulf and digest invaders

Antibodies are “Y” shaped proteins secreted by lymphocytes WBCs. They attach to the antigens on pathogens, targeting them for destruction by other WBCs.

The below text is loosely adapted from http://regentsprep.org/regents/biology/units/homeostasis/disease.cfm


When organisms are exposed to disease, they make specific antibodies. These destroy that pathogen during their first exposure to it. This is called the primary immune response.

Our immune system has a memory. If we’re ever exposed to that same antigen again, we’ll make antibodies rapidly in response to it This is  the secondary immune response.

Vaccinations use dead or weakened pathogens, or parts of them, to stimulate primary immune response

Why dead or weakened? Will not make the organism (us) sick

Because the vaccine has stimulated the immune system, the organism  now has memory. If there is a subsequent exposure, then body quickly fights it off.

Allergies and Auto-immune Diseases

In allergies, the body’s immune system produces chemicals in response to normally harmless substances which do not trouble other individuals. These chemicals make people with allergies feel sick.

In auto-immune diseases, the body’s immune system for usually unknown reasons may attack and destroy some its own cells. Some kinds of arthritis and degenerative diseases result from auto-immune diseases.

Two types of immunity

{ from http://kmbiology.weebly.com/immune-response—notes.html }

two types of immunity


  • Naturally antibodies are transferred from mother to child
    • Through the placenta before the baby is born
    • Through milk after birth
  • Artificial Passive Immunity à injecting antibodies from other animals/humans already immune to disease
    • Snake venom


  • Naturally antibodies are produced during an infection in response to antigens
  • Artificially by vaccines
  • Vaccines à substance consisting of weakened, dead, or incomplete portions of pathogens/antigens that when injected cause an immune response
  • Vaccines produce immunity because it prompts the body to act like it is infected

Other explanations of this process





T-Cells and B-Cells fighting a pathogen

Immune system T and B cells



Viral Attack (comic book)

Story Behind the Scenes

For Teachershttp://askabiologist.asu.edu/viral-attackhttp://askabiologist.asu.edu/body-depot/viral-attack_teachers
Click here to read the comic: “Viral attack!”



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