inclusion body

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An abnormal structure in a cell nucleus or cytoplasm having characteristic staining properties and usually composed of protein, occurring primarily in infectious diseases, especially viral infections such as rabies.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any small intracellular body found within another (characteristic of certain diseases)