ABSTRACT
S100 is a unique protein that was initially isolated in 1965 [1]. It derives its name from its solubility in a saturated ammonium sulfate solution. Although originally thought to be nervous system specific, its presence in diverse cell types and among many animal species is now well recognized. Few other antigens have been so voraciously sought after in diagnostic material. With the current advantage of 22 years of experience with this determinant, critics argue that there is an apparent lack of cellular specificity for its expression. Nevertheless, the demonstration that S100 may be diagnostically helpful in certain situations is supported by the approximately 1000 reports concerning its properties, in the English language literature of the last 7 years. After a brief review of its biochemistry and technical considerations, a detailed summary of the sites of immunolocalization of S100 protein is presented in the following sections.
