THE FINAL SHOWDOWN! This is the last episode on the immune system and also the very last episode of Crash Course Anatomy & Physiology. In it, Hank explains how the cellular immune response uses helper, cytotoxic, and regulatory T cells to attack body cells compromised by pathogens. He also explores how cytokines activate B and T cells, and what happens if your immune system goes rogue and starts causing autoimmune trouble.