66 zyxwvutsrqponm K. Fredriksen, zyxwvutsrqp A. Osei, A. Sundsfjord et al. Eur. J. Immunol. 1994. zyx 24: 66-70 Knut Fredriksen., Awuku Osei., Arnfinn Sundsfjord., Terje Traavik. and Ole Petter RekvigA Department of Virology., Institute of Medical Biology, University of Tromse and Department of Immunology and Transfusion MedicineA, University Hospital of Tromse. Tronse On the biological origin of anti-double-stranded (ds)DNA antibodies: systemic lupus erythematosus-relat ed anti-dsDNA antibodies are induced by polyomavirus BK in lupus-prone (NZBxNZW) F1 hybrids, but not in normal mice* We have recently demonstrated that polyomavirus BK and isolated BK double-stranded (ds)DNA have a strong potential for induction of anti-dsDNA antibodies. Here, data are presented that demonstrate that normal mice (a term used in this report for mice not predisposed to a lupus-like syndrome) of four different strains responded to both BK virus and BK dsDNA by producing transient antibodies binding preferentially to the viral dsDNA itself. These antibodies did not bind in the Crithidia luciliae assay, and did not seem to be of pathogenic significance, as neither signs of proteinuria nor immunochemical signs of glomerulonephritis developed in these mice. In contrast, 5-week-old (NZBxNZW)Fl mice developed strong and persistent anti-dsDNA antibodies in response to BK virus and BK dsDNA, with similar features to those of anti-dsDNA antibodies from individuals with systemic lupus erythematosus: they reacted strongly in the Crithidia luciliae assay and cross-reacted with viral as well as with mammalian dsDNA. Furthermore, persistent proteinuria and glomeru- lonephritis, with demonstrable heavy mesangial deposits of immune complexes containing IgG anti-dsDNA antibodies, developed 2-3 months earlier than in spontaneously autoimmune control mice. The relevance of these observations to a viral origin of anti-dsDNA antibodies in lupus is discussed. 1 Introduction The origin and biological nature of the antigen(s) that induce antibodies to double-stranded (ds)DNA in SLE are still unknown [1]. However, several recent reports from our group 12-51 and from others [6] demonstrate that dsDNA itself may represent the selective stimulus for anti-dsDNA antibody formation. These reports are supported by gene- tical studies of autoimmune anti-dsDNA antibodies [7-91 that strongly indicate specific antigenic stimulation, and that suggest the stimulating antigen probably is dsDNA itself. The anti-dsDNA antibodies induced by immunizations were relatively specific for the inducing dsDNA antigen [4-61, and they did not, with few exceptions [2], bind the Crithidia kinetoplast, indicating that these antibodies have restricted specificities as compared to lupus-derived anti- bodies. Analogous experiments performed in the lupus- [I 120041 zyxwvu * This study was supported by the Norwegian Research Council (NAVF). the Norwegian Cancer Society (DNK), Erna og Olav Aakre Foundation and the Birger Torsted Foundation. Correspondence: Knut Fredriksen, Department of Virology, Insti- tute of Medical Biology, University of Tromso, N-9037 Tromso, Norway (Fax: 47 77 62 63 04) Abbreviations: (NZBNV): (NZBxNZW)Fl mice dsDNA: Double-stranded DNA CT Calf thymus MBSA: Methylated BSA SP: Virus structural proteins Key words: Autoimmunity / Anti-DNA / Systemic lupus erythe- matosus / (NZBxNZW)F, mice / BK virus prone MRL mouse strain, using mammalian dsDNA as antigen [lo], did not result in significant anti-dsDNA antibodies, or in acceleration of disease development. In the present experiments we have immunized different mouse strains with BK virus or BK dsDNA, and analyzed the immune responses to dsDNA in mice not predisposed to a lupus-like syndrome zyxw vs. lupus-prone (NZB/W) mice. The induced antibodies from the NZB/W hybrids, but not those from the other strains, were positive in the Crithidia luciliae assay and induced immune complex glomerulo- nephritis, i.e. characteristics shared by the pathogenic lupus-like anti-dsDNA antibodies produced spontaneously later. 2 Materials and methods 2.1 Immunization of mice BK virus, BK dsDNA and calf thymus (CT) dsDNA was purified as described [3, 41. C57BL/6 and C3H mice were obtained from Charles River (FRG), and BALB/c, NZW/OLA/HSD (NZW) and NZB/W mice from Harlen Olac (GB). Fifty-one mice were immunized at the age of 5-6 weeks with either sterile PBS (four normal and five NZB/W mice), 100 pg pure methylated BSA (MBSA, Sigma; two C57BL/6 and four NZB/W mice), 100 pg protein-free BK dsDNA (four C57BL/6 and four NZB/W mice), 100 pg linear BK dsDNA complexed with 30 yg MBSA (nine normal and six NZB/W mice), or 100000 hemagglutination units of purified, infectious BK virus (eight normal and five NZB/W mice). Thus, mice of all strains and both sexes were included in all groups except for the groups receiving MBSA and protein-free BK dsDNA. 001 4-2980/94/01O1-0066$10.00 + .25/0 zyxwvuts 0 VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1994