OpenStax
Open Stax: Anatomy & Physiology: Leukocytes and Platelets
This study of white blood cells includes informational reading material, illustrated diagrams, vocabulary, and self-checking review and application questions.
PBS
Pbs: The Immune System's Battle Against Disease
A "just for fun" Shockwave game that allows you to control an animated macrophage against an invading virus. You must figure out how the let the Helper T-cells get involved.