This is a dimeric acidic calcium-binding protein.  It was first isolated from the central nervous system. It is a dimer with alpha and beta subunits, able to combine in three isoforms S-100ao (alpha dimer), S-100a (alpha-beta isoform) and S-100b (beta dimer). There are structural similarities to the calcium-binding domain of calmodulin. It is a calcium flux regulator. The name derives from its solubility in 100% saturated ammonium sulphate.

It has more recently become apparent that there is a whole family of related calcium binding proteins.

Polyclonal and monoclonal antibodies are available. Some of the monoclonal antibodies are specific to alpha or betas subunits and so have a more limited range of immunoreactivity than do the polyclonal antibodies.

Immunohistochemical expression

S-100 is present in the nucleus and cytoplasm of:

It is expressed by the tumours derived from the above cells:







sustentacular cells also stain positively in carcinoids of foregut and midgut but not hindgut1

Diagnostic utility

The diagnostic value is limited by the widespread expression of S-100. 


1Al-Khafaji et al. Immunohistologic analysis of gastrointestinal and pulmonary carcinoid tumours. Human Pathol 1998;29:992-9.

2Diagnostic Immunohistochemistry edited by Professor D. J. Dabbs, page 70

3Zembowicz, A., S. R. Granter, et al. (2002). "Amelanotic cellular blue nevus: a hypopigmented variant of the cellular blue nevus: clinicopathologic analysis of 20 cases." Am J Surg Pathol 26(11): 1493-1500.

This page last revised 21.12.2001.

©SMUHT/PW Bishop