An immunostimulatory oligodeoxynucleotide containing a cytidine-guanosine motif protects senescence-accelerated mice from lethal influenza virus by augmenting the T helper type 1 response.

The SAM-P1 strain of senescence-accelerated model mice shows an impaired T helper type 1 (Th1) immune response upon infection with influenza virus, which results in high susceptibility to the virus. Treatment of spleen cells from SAM-P1 mice with an immunostimulatory oligodeoxynucleotide containing a cytidine-guanosine motif (CpG ODN) in vitro increased the ratio of the titre of IFN-gamma to that of IL-4. Administration of CpG ODN to SAM-P1 mice generated satisfactory virus-specific cytotoxic T-lymphocyte responses and natural killer cell activation and the virus-specific immunoglobulin (Ig) isotype switched from IgG1 to IgG2a. Virus growth in the lungs of CpG ODN-treated SAM-P1 mice was cleared quickly and mice survived the lethal influenza virus infection. It could be inferred that a possible mechanism of CpG ODN for normalization of senescence-associated dysregulation of the Th1/Th2 balance involves the upregulated expression of CD154 and CD40 molecules on immune-competent cells. These results suggest that CpG ODN could contribute to the development of a protective strategy against infectious diseases, especially among immunocompromised elderly persons, by stimulating Th1 immune responses.