Genes linked to the MHC class II contribute to human and murine lupus, but multiple genes are required to produce and upregulate pathogenic autoantibodies. In NZB/NZW mice, nephritogenic IgG anti-dsDNA is provided by NZW (H-2z), but the origin of the upregulating signals is unknown. They could be from NZB (H-2d) or NZW (H-2z) or require heterozygocity. Our aim was to determine whether NZW can provide upregulating signals for the nephritogenic autoantibody introduced to normal mice via transgenes encoding a NZB/NZW IgG2a antibody to DNA. These transgenic mice spontaneously secrete serum IgG2a anti-DNA, some develop clinical nephritis with proteinuria and azotemia, but none die of fatal nephritis. We bred mice to produce offspring of H-2b/d, H-2b/b, H-2b/z and H-2d/z haplotypes (H-2b, H-2d and H-2z derived from C57BL/6, BALB/c and NZW, respectively). Transgenic H-2b/d mice had significantly higher levels of serum anti-DNA antibodies compared with H-2b/b haplotypes from 20 to 40 weeks of age (P < 0.05). However, unlike NZB/NZW mice, they did not show sustained upregulation of anti-DNA antibodies. The serum levels of IgG anti-DNA of transgenic mice declined after 30 weeks of age. In order to determine whether NZW can provide upregulating signals, we introduced the NZW background into transgenic H-2b/d mice in an attempt to increase both quantities of anti-DNA and prevalence of nephritis. However, serum levels of anti-DNA antibodies were similar in transgenic mice of H-2b/z and H-2d/z haplotypes. The anti-DNA levels declined with age in both groups. No mice developed fatal nephritis.(ABSTRACT TRUNCATED AT 250 WORDS)