Monoclonal antibody CD133-2 (AC141) against hematopoietic stem cell antigen CD133 shows crossreactivity with cytokeratin 18

CD133 is an antigen expressed on hematopoietic progenitor cells and on some epithelial cells. We previously reported that a commercially available antibody against CD133, CD133-2/AC141, also reacted with an intracellular protein in placental trophoblasts. Here we show by 2D electrophoresis and mass spectroscopy that this reactivity is with cytokeratin 18, a cytokeratin present in most simple epithelia. Immunohistochemistry (IHC) with CD133-2/AC141 on a trophoblast cell line displayed a staining pattern typical for the cytoskeleton. Cryostat sections of stratified epithelia lacking cytokeratin 18 did not react with CD133-2/AC141. In conclusion, care must betaken not to misinterpret staining patterns using CD133-2/AC141 in IHC.