This website was invaluable to me for TAQ 4 and explained the role of helper T cells in detail but in a straightforward and understandable manner, so thought I'd share
Wow! How did I not know about the Khan Academy before. This guy has just made me jump around the living room telling my other half all about B-Cells, T-Cells, antigens etc. He now thinks I'm a complete nerd, but that's ok because I understand it!!!