An excellent immunology book at the post-graduate level is:
Fundamental Immunology, 3rd ed., edited by William E. Paul, published
by Raven Press, N.Y., 1993, ISBN 0781700221. It is 1490 pages long
and is a collection of chapters written by experts in their
respective fields. A much shorter book that is very popular is:
Cellular and Molecular Immunology, 2nd ed., by Abul K. Abbas et al.,
W.B. Saunders Co., Philadelphia, 1994, ISBN 0-7216-5505-X. I don't
know if one would call it a postgraduate-level book, but many post-
graduates buy it for their own use.
Jack Komisar