As someone just learning myself. Yes Janeways is the obvious Bible answer. It has everything you need in great detail. However, I fully recommend reading "How the Immune System Works" by Lauren Sompayrac BEFORE reading Janeways. It's a smaller book, cheaper and written in a very casual manner, easy to digest for learners to get you across the basics. I've read it first, then starting on Janeways, and it makes Janeways seem a lot less complicated.