All animals possess a non-specific defense system called the innate immune system. Innate immune responses attack microbes indiscriminately.
Vertebrates have an additional and powerful immune response called adaptive immunity. This feature focuses on elements of the adaptive immune system.
Also featured on the HHMI DVD, AIDS: Evolution of an Epidemic, available free from HHMI.
Download the accompanying worksheet (PDF) for students to complete as they go through the Click and Learn.