Green fluorescent protein modified to bind DNA initiates production of anti-DNA antibodies when expressed in vivo

Abstract

Studies have clearly demonstrated that DNA itself is not or scarcely immunogenic in experimental animals. We have previously demonstrated that linking human polyomavirus large T-antigen to DNA rendered DNA immunogenic irrespective of the source or the structure of DNA. As an alternative to this artificial system, in vivo expression of the DNA binding protein large T-antigen of human polyomaviruses also resulted in the production of anti-DNA antibodies. This observation demonstrates that the large T-antigen concept is operational in vivo and supports the idea that complex formation between a non-self DNA-binding protein and DNA renders DNA immunogenic in analogy to a hapten-carrier model. To further investigate this model, the DNA binding domain (DBD) of a self-protein (glucocorticoid receptor) was linked to a non-DNA binding non-self protein, the green fluorescent protein (GFP). Immunization of mice with an expression plasmid for this fusion protein resulted in the production of anti-DNA antibodies, while mice inoculated with either a plasmid encoding the GFP or a plasmid encoding the DBD of the glucocorticoid receptor failed to produce anti-DNA antibodies. These results demonstrate that DNA may become immunogenic through in vivo association with any non-self DNA binding protein. Considering these data in context of results obtained with the polyomavirus large T-antigen, one may conclude that viral DNA-binding proteins may affect the regulation of immune tolerance to DNA and nucleosomes in vivo.