2. Immune System Overview

3. What causes disease? ► An organism that causes an infection or disease is called a pathogen ► Types of pathogens include virus, bacteria, fungus, and protozoa

4. Pathogen A antigen A ► Pathogens have proteins on their cell membrane, and these proteins have unique shapes. ► These proteins are called antigens.

5. Pathogen A antibody A antigen A ► The body makes antibodies to fit the shape of these antigens.

6. Pathogen A antibody A antigen A ► Antibodies are produced by white blood cells. ► WBCs recognize pathogens that you’ve already been exposed to. By remembering them, you won’t get sick from the same pathogen.

7. Pathogen A White Blood Cell antibody A antigen A ► White blood cells engulf, or eat, pathogens. ► This is called phagocytosis.

8. Pathogen antibody A Antibody A antibody antigen White Blood Cell

9. How does your body know that these pathogens are harmful? ► Every organism’s cells have antigens ► Antigens act like name tags ► Antigens have their own unique or specific shape ► This allows your body to recognize things that don’t belong inside you.