National Center for Biotechnology Information
www.ncbi.nlm.nih.gov/?
Has this textbook free online, with search ability.
Immunobiology: The Immune System in Health and Disease. 5th edition.
"This book is intended as an introductory text for use in immunology courses for medical students, advanced undergraduate biology students, graduate students, and scientists in other fields who want to know more about the immune system."
http://www.ncbi.nlm.nih.gov/books/NBK10757/
Autoimmune responses are directed against self antigens
http://www.ncbi.nlm.nih.gov/books/NBK27155/#A1932