immune system

2. A cell or group of cells that filters material from the blood, processes that material, and secretes it either for use again in the body or to be eliminated as waste.
4. Soft tissue located in the hollow centers of most bones; the marrow contains developing red blood cells, white cells, platelets and cells of the immune system.
7. a harmful substance which causes the body to make antibodies as a response to fight disease.
9. immune cells that are formed in the bone marrow but matured in the thymus.
12. a type of general protection; example:the skin.
13. pathogen; not actually "alive," and consists only of a fragment of DNA with a protective coat.
14. a white blood cell.
15. anything that can invade the body and cause disease.

1. an abdominal organ that filters the blood, recycles old red blood cells, and stores platelets and white blood cells.
3. the body's defense against infections.
5. a type of white blood cell that gives rise to antibodies, also known as B Lymphocyte.
6. an immune protein that is produced when an antigen enters the body.
8. pathogen; single celled organism, completely independent, and reproduces quickly.
10. a small white blood cell that plays a large roll in defending the body against disease.
11. tricks the body's natural defenses into reacting against a pathogen that is not attacking the body; acquired immunity.