S100 proteins

Calcium-binding proteins with a molecular mass of 9-13 kDa, which influence a variety of different cellular processes. The S100 proteins include at least 25 members that are expressed in a wide variety of cell types:

• S100B: in astrocytes, adipocytes, melanocytes and chondrocytes.
• S100A1: in cardiomyocytes, in cells of the salivary glands, in kidney and muscle cells, in nerve cells of the hippocampus.
• S100A6: in connective tissue cells and muscle cells.
• S100A8 and S100A12: primarily in phagocytes. The serum concentration correlates with the activity of inflammatory diseases.
• S100A9: Screening parameter for prostate carcinoma.
• S100A15: In normal epidermis, S100A15 is expressed by basal and differentiated keratinocytes, melanocytes and Langerhans cells of the epidermis. Within the pilosebaceous unit, S100A15 is found in the inner and outer root sheath and in the basal layer of the sebaceous gland. In the dermis, S100A15 is produced by dendritic cells, smooth muscle cells, endothelial cells and fibroblasts to control tissue regeneration.

S100 antibodies are frequently used indermatohistology. Due to the small size of the S100 proteins, formalin fixation is necessary for visualization in the tissue. It can be washed out of cryostat sections and insufficiently fixed tissue. S100 staining can be nucleolar or cytoplasmic. S100 marks: melanocytes and nevus cells, Langerhans cells, Schwann cells, myoepithelial cells, cartilage cells, etc. It is the most important marker for desmoplastic melanocytic markers.

S100 i.S (melanoma screening): in malignant melanomas, S100 positivity is often found even when other melanocytic markers are no longer formed due to progressive de-differentiation. Salivary gland tumors and tumors of the eccrine sweat glands often also show an expression of S100.

Note! For melanoma screening, the absolute values are less important than the fluctuations over time.

1. Hantschke M et al (2016) Immunohistological techniques. In: L. Cerroni et al. histopathology of the skin. Springer Publishing House Berlin-Heidelberg p. 33.
2. Sedagath F et al (2008) S100 protein family and its application in clinical practice. Hippocratia 12: 198-204