HUMAN T-LYMPHOCYTES AND HEMATOPOIETIC-CELL LINES EXPRESS CD24-ASSOCIATED CARBOHYDRATE EPITOPES IN THE ABSENCE OF CD24 MESSENGER-RNA OR PROTEIN

The CD24 surface antigen is a small glycophosphatidylinositol (GPI)-an chored glycoprotein found on human granulocytes and most B lymphocytes . Many CD24 monoclonal antibodies (MoAbs) have been described that ide ntify several epitopes, with the majority of them related to carbohydr ate structures associated with the CD24 molecule. Considerable variati on has been observed in the apparent tissue distribution of the CD24 a ntigen depending on the MoAb used, and hence the CD24 epitope studied. In this study, CD24 expression by human cell lines and normal hematop oietic cell populations was assessed using a panel of carbohydrate and protein core-specific CD24 MoAbs and reverse transcriptase polymerase chain reaction (RT-PCR) analysis. A number of CD24 carbohydrate epito pe-reactive MoAbs bound to both T lymphocytes and several hematopoieti c cell lines, despite the absence of concomitant CD24 mRNA or detectab le surface CD24 core protein in the same cells. This additional CD24 M oAb reactivity on T lymphocytes was, in common with that observed on g ranulocytes (CD24 protein(+)), specifically inhibited by the presence of both sialyllactose and mucin. Similarly, the binding of carbohydrat e epitope-reactive CD24 MoAb was reduced on both T lymphocytes and gra nulocytes by pretreatment with phospholipase C, pronase, or neuraminid ase. Together, the data indicate that a number of CD24-associated carb ohydrate epitopes have a broader tissue distribution than the CD24 pro tein and are expressed on additional GPI-linked molecule(s). These fin dings have immediate implications for both leukemia phenotyping and at tempts to examine CD24 function with CD24 MoAb. (C) 1996 by The Americ an Society of Hematology.