Effects of bacterial DNA on cytokine production by (NZB/NZW)F₁ mice

Microbial DNA has multiple immune effects including the Capacity to induce polyclonal B cell activation and cytokine production in normal mice. We recently described the accelerated induction of anti-DNA Abs in NZB/NZW mice immunized with Escherichia coli (EC) dsDNA; paradoxically these mice developed less renal disease than unimmunized mice or mice immunized with calf thymus DNA. We postulated that alterations in cytokine production induced by bacterial DNA may play a key role in renal protection. To determine the effect of bacterial DNA on cytokine production in NZB/NZW mice, we measured the serum cytokine levels, cell culture supernatant cytokine levels, and number of cytokine-producing splenocytes in NZB/NZW mice injected with EC DNA, calf thymus DNA, or an immune active oligonucleotide. There was a 10- to 25-fold increase in the number of cells secreting IFN-γ compared with IL-4 in mice immunized with EC DNA. IL-12-secreting cells were also increased by bacterial DNA immunization. In parallel with the increase in IFN-γ secreting cells, there was a significant rise in serum IFN-γ levels in mice receiving EC DNA. These results indicate that EC DNA modulates systemic cytokine levels in NZB/NZW mice, selectively increasing IL-12 and IFN-γ while decreasing IL-4 production. The cytokine response of NZB/NZW mice to bacterial DNA may be of significance in disease pathogenesis and relevant to the treatment of lupus-like disease.