CD55 cell surface antigen is a GPI linked molecule also known as decay accelerating factor (DAF). CD55 is expressed by a wide range of cell types. CD55 is the complement regulatory protein, decay accelerating factor (DAF) (Lublin and Atkinson 1989). Human CD55 is a ~70 kDa glycoprotein (in erythrocytes) anchored in the membrane by glycosylphosphatidylinositol tail. In other cells the apparent molecular weight is somewhat larger. It has a substantial content of O-glycans, and also on N-glycan. DAF binds to activated C4b or C3b complement fragments on the cell surface, preventing the assembly and accelerating the decay of both classical and alternative pathways. DAF carries the Cromer related blood group antigens. DAF has a wide distribution on cells in non-hemopoietic tissues, particularly epithelium and is specifically found at the fetal-maternal interface in placenta (Holmes et al. 1990 and Yang et al. 2009). Soluble forms of DAF are found, for example, in plasma, saliva and urine (Medof et al. 1987). The antigen on erythrocytes is pronase and chymotrypsin sensitive, but resistant to trypsin. Applications: Suitable for use in Immunohistochemistry and Western Blot. Not recommended for staining erythrocytes. Other applications not tested. Recommended Dilution: Immunohistochemistry: Frozen sections Optimal dilutions to be determined by the researcher. Positive Control: Human tonsil Storage and Stability: Store product at 4C if to be used immediately within two weeks. For long-term storage, aliquot to avoid repeated freezing and thawing and store at -20C. Aliquots are stable at -20C for 12 months after receipt. Dilute required amount only prior to immediate use. Further dilutions can be made in assay buffer. Note: Sodium azide is a potent inhibitor of peroxidase and should not be added to HRP conjugates. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Note: Applications are based on unconjugated antibody.
