Identification of CpG oligonucleotide sequences with high induction of IFN-alpha/beta in plasmacytoid dendritic cells

The immature plasmacytoid dendritic cell (PDC) is identical with the princi pal type I IFN-producing cell upon viral infection. Oligodeoxynucleotides w hich contain unmethylated CpG motifs (CpG ODN) are recognized by the verteb rate immune system. Previously, we described CpG ODN that strongly activate human B cells and human blood dendritic cells. Mere we describe distinct C pG-containing oligonucleotide sequences which, in contrast to previously de scribed CpG ODN, induced high amounts of IFN-cr and IFN-P in peripheral blo od mononuclear cells (PBMC). Intracellular staining for IFN-a revealed that within PBMC CpG ODN-induced IFN-alpha is produced exclusively by PDC. Unli ke IFN-cr, TNF-cr is upregulated in PDC by all CpG ODN tested. Purified PDC responded to CpG ODN, demonstrating direct activation of PDC by CpG ODN. T he most active sequence induced the production of up to 5 pg: IFN-alpha per single PDC, resulting in more than 400 ng/ml IFN-alpha in the supernatant of PBMC enriched; for PDC. The potency of CpG ODN to stimulate IFN-a correl ated with their ability to stimulate NK cell lytic activity, while purified NK cells did not respond. to CpG ODN. IFN-gamma production in PBMC was dep endent on CpG ODN-induced IFN-alpha/beta as demonstrated by IFN-alpha/beta blocking antibodies. IFN-alpha -inducing CpG ODN strongly supported IFN-gam ma production of TCR-triggered CD4 T cells but were less active than other CpG ODN in stimulating B cells. In conclusion our results demonstrate that particular CpG. ODN sequences exist which, due to high IFN-alpha/beta induc tion in PDC, induce a set of immune responses typical for viral infection.