Howard Hughes Medical Institute
Hhmi: Bio Interactive: Cells of the Immune System
Slideshow with embedded video and audio explains our immune system and how it works. Includes a worksheet handout.
Khan Academy
Khan Academy: Innate Immunity
The human body requires a multilayered immune system to keep it running smoothly. The two main classes of the immune system are the innate immune system and the adaptive immune system, or "acquired immunity". This article discusses the...
CK-12 Foundation
Ck 12: Biology: Immune System Part I Study Guide
This study guide on the immune system covers key terminology and the different lines of defense the human body has to protect itself against pathogens. It is available for download with free registration.