CD15 is actually a number of different cell surface glycoproteins and glycolipids that all have in common either the unsialylated or sialylated LewisX (LeX, CD15s) antigens. It is best to consider CD15s separately but historic antibodies detected both CD15 and CD15s which could cause confusion.
The key unsialylated CD15 epitope is a trisaccharide with the structure Galβ(1-4)Fucα(1-3)GlcNAc that mediates mediates phagocytosis and chemotaxis and that is expressed as a relative simple glycolipid on:
- Mature granulocytes.
- Certain activated lymphocytes
- Leukaemic myeloid and monocytic cells (particularly acute promyelocytic leukaemia)
- Reed-Sternberg and Hodgkin's cells in Hodgkin's lymphoma
It is also expressed in some (about 50%) of adenocarcinomas such as colon and breast carcinoma. It is likely to be involved in cellular recognition during fertilization, embryogenesis and neural development and appears to be a marker for pluripotent stem cells.
It is used in histopathology to identify Reed-Sternberg cells where it is heavily expressed in the membrane and golgi apparatus, and its presence can suggest adenocarcioma rather than say mesiothelioma.
Myeloid maturation is accompanied by relative loss of CD15s and gain of CD15 expression.
Sialyl-Lewis x (CD15s, sLex, NeuNAcα2-3Galβ1-4(Fucα1-3)GlcNAc) is essentially the epitope that makes humans as it is key to human fertilisation as well as being expressed on cancer cells and with leukocytes is the major ligand for endothelial E-selectin and P-selectin.