Cytokine induction by carriers of Raf-1 or VEGFR2 siRNA in Balb/c mice. Several branched carriers that varied in their histidine and/or lysine content were examined for their ability to induce (a) IFN-α or (b) IL-6 in Balb/c mice. Six hours after the siRNA complexes were administered intravenously, serum cytokine levels were determined. Of the carriers of siRNA, H3K(+H)4b increased cytokine levels the least. Vehicle alone values: IFN-α, IL-6, not detectable. *P < 0.05, **P < 0.01, ***P < 0.001, H3K(+H)4b versus other HK, liposomal carriers of Raf-1 or VEGFR-2 siRNA (one-way analysis of variance with Bonferroni t-test). HK, histidine-lysine; IFN, interferon; IL, interleukin; siRNA, small interfering RNA; VEGFR2, vascular endothelial growth factor receptor-2.