A Novel Function of Phosphorothioate Oligodeoxynucleotides as Chemoattractants for Primary Macrophages

Phosphorothioate cytosine-guanine oligodeoxynucleotides (CpG PS-ODNs) has been reported to induce Th1 immune responses against coadministered Ags more efficiently than phosphodiester CpG ODNs (CpG PO-ODNs). Here, we demonstrated that PS-ODNs, but not PO-ODNs, have a chemotactic effect on primary macrophages, which is independent of the CpG motif. In addition, the conjugation of a hexameric dG run (dG(6) run) at the 3' terminus reduced the concentration required for the optimal chemotactic activity of PS-ODNs by approximately 10-fold. Endosomal maturation blockers, such as monensin and chloroquine, inhibited the chemotactic effect of PS-ODNs. The inhibition of the activities of p38 mitogen-activated protein (MAP) kinase, and extracellular signal-related kinases (ERKs) as well as phosphoinositide 3-kinase with their specific inhibitors also resulted in suppressing the chemotaxis of primary macrophages induced by PS-ODNs. These results indicate that the PS-ODN-mediated chemotaxis requires the activation of ERKs, p38 MAP kinase, and phosphoinositide 3-kinase as well as endosomal maturation. In addition, the phosphorylations of the p38 MAP kinase, ERKs, and protein kinase B, Akt, were induced by PS-ODN, which were further enhanced by the presence of both a dG(6) run and CpG motifs. Our findings suggest that the chemotactic activity of PS-ODNs may be one of the mechanisms by which PS-ODNs exhibit stronger immunomodulatory activities than PO-ODNs in vivo.