Immunostimulatory properties of genomic DNA from different bacterial species

Bacterial DNA has potent immunological properties because of its content of immunostimulatory sequences centering on CpG motifs. To investigate whethe r DNA from various bacterial species differ in these properties, the activi ty of a panel of DNA was assessed in in vitro cultures of murine spleen cel ls. This panel varied in base composition and included DNA from Clostridium perfringens (CP), Escherichia coli (EC), Micrococcus lysodeikticus (MC), S taphylococcus aureus (SA), and, as a mammalian DNA control, calf thymus (CT ) DNA. In assays of IL-12 and IFN-gamma production as well as B cell mitoge nesis, these DNA showed marked differences in their immunostimulatory activ ity. For both cytokine and B cell responses, EC DNA demonstrated the highes t activity while CP DNA had the lowest activity among the bacterial DNA. To determine whether differences in stimulatory capacity resulted from differ ences in cell uptake, the activity of DNA complexed with lipofectin was tes ted. While the addition of lipofectin to DNA increased stimulation by all D NA, it did not change the relative potency of the DNA tested. These results indicate that bacterial DNA differ in their immunostimulatory capacity, mo st likely reflecting their content of CpG motifs. These differences could a ffect the induction of innate immunity as well as the consequences of infec tion.