Autoimmunogenicity of the helix-loop-helix DNA-binding domain.

Nonimmunogenic character of native DNA, and its high immunogenicity when presented in complex with the DNA-binding proteins indicate that the latter might contain molecular triggers of anti-DNA response. To find if this is the case, we have evaluated the autoimmunogenic potential of the main DNA-binding domain of HIV-1 reverse transcriptase that belongs to the canonical helix-loop-helix type. BALB/c mice were immunized with a peptide representing the domain, alone or in complex with the fragmented human DNA in the presence of an adjuvant. Mice were assessed for specific antibodies, autoantibodies against a panel of self-antigens; glomerular immunoglobulin deposition; and for the signs of autoimmune disease, such as proteinuria, and changes in the blood components. Immunization with the adjuvanted peptide-DNA complex induced autoantibodies against double-stranded DNA, histones, heterochromatin, and kidney proteins; glomerular IgG and IgA deposition; proteinuria; thrombocytopenia, and anemia. Altogether, this identifies the helix-loop-helix DNA-binding domain as one of the molecular triggers of autoimmunity to DNA and DNA-associated proteins. The experiments cast new light on the role of the DNA-binding retroviral proteins in the induction of autoimmunity, and on the origins of autoimmune complications in the microbial infections in general. It also implies that choosing the DNA-binding proteins as vaccine candidates should be done with precaution.