Liposomes are known to enhance the activity of K- (B-) type CpGs which trigger the production of IL-12. In the present invention, the surprising finding was made that liposomes also enhance the activity of D- (A-) type CpGs, leading to the production of IFNα in vivo. These findings are relevant for the humans situation, since IFNα rather than IL-12 is the key cytokine for the induction of Th1 responses and anti-viral protection in humans.