Differential expression of SIRPα and SIRPβ on distinct subsets of primary DCs.

Cells from whole blood were stained with anti-ILT1 antibody followed by FITC-labeled goat antirat antibody. After washing, cells were labeled with PCy5-conjugated anti-CD3, -CD14, -CD16, -CD19, and -CD56 MoAb; PE-conjugated anti-ILT3 MoAb; and biotinylated MoAbs SE5A5 and B1D5 or a biotinylated control antibody. In the final step, streptavidin-allophycocyanin was added. Primary DCs in human PB are included within lineage (lin)⁻/low side-scatter cells (top left). Differential expression of ILT1 and ILT3 receptors on these cells allows the identification of 2 distinct subsets of primary DCs (top right). ILT3⁺ILT1⁻ cells correspond to plasmacytoid dendritic cells. ILT3⁺ILT1⁺ cells correspond to myeloid DCs. SIRPα (analyzed with MoAb SE5A5) is expressed on both subsets and is particularly bright on ILT3⁺ILT1⁺ DCs. SIRPβ (analyzed with MoAb B1D5) is expressed on a significant percentage of ILT3⁺ILT1⁺ DCs (30%-70% in different individuals) and only on few ILT3⁺ILT1⁻ DCs (5%-10%). Bars on the left of the histograms indicate the region in which 99% of the control cells stained with isotype-matched control antibodies were found.