IDENTIFICATION OF A NOVEL DENDRITIC CELL-SURFACE ANTIGEN DEFINED BY CARBOHYDRATE SPECIFIC CD24 ANTIBODY CROSS-REACTIVITY

Dendritic cells (DC) are characterized as leucocytes that lack mature lineage specific markers and stimulate naive T-lymphocyte proliferatio n in vitro and in vivo. The mouse heat stable antigen (HSA) participat es in T lymphocyte co-stimulation and is expressed by DC isolated from thymus, skin and spleen. The human HSA homologue, CD24. is predominan tly expressed by B lymphocytes and granulocytes, but its expression on DC has not been studied in detail. CD24 clearly participates in B-lym phocyte signalling but co-stimulatory activity for T lymphocytes has n ot yet been described. We have examined the expression of CD24 on huma n peripheral blood DC populations isolated directly or following in vi tro culture. The CD24 antigen was absent from blood DC; however, cross -reactive, sialylated carbohydrate epitopes were detected on DC with s ome CD24 monoclonal antibodies (mAb). These CD24 mAb define a protein surface antigen, which is expressed by an immature or resting subpopul ation of peripheral blood DC and is downregulated following activation /differentiation in vitro.