Activation of granulocytes by direct interaction with dendritic cells

Granulocytes from human peripheral blood were co-cultured with conventional dendritic cells (cDC) or plasmacytoid DCs (pDC) to examine the effects of DCs on the activation or function of granulocytes. After co-culture of granulocytes with DCs, expression of the activation markers of granulocytes (CD63 and CD64) was up-regulated, and increased expression of CD50, the activation marker and ligand for CD209 (DC-SIGN) was also observed. The interaction of granulocytes with DCs was visualized as the cluster where DCs, especially cDCs, were surrounded by granulocytes to form a 'rosette'. After co-culture of granulocytes with cDCs, the secretion of elastase from granulocytes was enhanced significantly when examined cytohistochemically and by enzyme-linked immunosorbent assay. An increase in myeloperoxidase (another activation index of granulocytes) was also observed after co-culture with DCs. These findings suggest the functional and phenotypical activation of granulocytes by interaction with DCs. Furthermore, we examined the involvement of adhesion molecules in the granulocyte-DC interaction, and found that CD209 participates to some extent in this interaction.