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Identification of a novel dendritic cell surface antigen defined by carbohydrate specific CD24 antibody
L A Williams1, A D McLellan, K L Summers
1Haemetology Immunology Research Group, Christchurch School of Medicine, New Zealand.
Insights
CD24, a molecule studied in B-cells, is not found on human peripheral blood dendritic cells (DC). However, immature DC express a related antigen that decreases upon activation.
Area of Science:
- Immunology
- Cell Biology
Background:
- Dendritic cells (DC) are crucial leukocytes for initiating immune responses.
- The mouse heat stable antigen (HSA) is involved in T-lymphocyte co-stimulation and expressed by mouse DC.
- The human homologue of HSA, CD24, is mainly on B-lymphocytes and granulocytes, with limited study on DC.
Purpose of the Study:
- To investigate the expression of CD24 on human peripheral blood dendritic cell populations.
- To determine if CD24 plays a role in T-lymphocyte co-stimulation in humans.
Main Methods:
- Isolation of human peripheral blood dendritic cell populations.
- Analysis of CD24 expression using monoclonal antibodies (mAb) on DC.
- Assessment of CD24 expression on both freshly isolated and in vitro cultured DC.
Main Results:
- CD24 antigen was found to be absent on circulating human peripheral blood DC.
- Cross-reactive sialylated carbohydrate epitopes were detected on DC using certain CD24 mAb.
- These epitopes define a surface antigen present on immature/resting peripheral blood DC.
- Expression of this antigen was downregulated upon DC activation and differentiation in vitro.
Conclusions:
- Human peripheral blood dendritic cells do not express the CD24 protein.
- Immature or resting human dendritic cells express a CD24-related sialylated carbohydrate epitope.
- This epitope is downregulated during dendritic cell activation and maturation.
Abstract:
Dendritic cells (DC) are characterized as leucocytes that lack mature lineage specific markers and stimulate naive T-lymphocyte proliferation in vitro and in vivo. The mouse heat stable antigen (HSA) participates in T lymphocyte co-stimulation and is expressed by DC isolated from thymus, skin and spleen. The human HSA homologue, CD24, is predominantly expressed by B lymphocytes and granulocytes, but its expression on DC has not been studied in detail. CD24 clearly participates in B-lymphocyte signalling but co-stimulatory activity for T lymphocytes has not yet been described. We have examined the expression of CD24 on human peripheral blood DC populations isolated directly or following in vitro culture. The CD24 antigen was absent from blood DC however, cross-reactive sialylated carbohydrate epitopes were detected on DC with some CD24 monoclonal antibodies (mAb). These CD24 mAb define a protein surface antigen, which is expressed by an immature or resting subpopulation of peripheral blood DC and is down-regulated following activation differentiation in vitro.
