Fact 1: Antigens are found on cancer cells and the cells of transplanted organs.

Fact 2: Anything that can trigger an immune response is called an antigen.

Given the two facts above, answer the question "What can trigger immune response?" with the following options: 
- harmful substances
 - Transplanted organs
 - desire
 - an area swollen with pus
 - death
 - pain
 - colors of the spectrum
 - Contaminated wounds


 

  Transplanted organs       