CD24 antigen is expressed throughout Bcell development and is downregulated as bone marrow progenitors mature. CD24 expression is lost when human B-cells become plasma cells. The cellular function for human CD24 is unknown so far. Diagnostically, it can serve as a marker for staging B-cell development, and it is expressed at high levels in small cell lung carcinoma. CD24 is a member of a family that also includes Heat Stable Antigen HSA and CD52. It is a glycosylphosphatidylinositol (GPI) anchored glycoprotein.Synonyms: HSA, Signal transducer CD24, Small cell lung carcinoma cluster 4 antigen, X62 heat stable antigen