We have previously demonstrated the influence of the I-Abm12 gene mutation on the appearance of IgG anti-dsDNA antibodies when placed on an NZB genetic background. To further enhance our understanding of the interaction of the bm12 mutation on disease expression, lethally irradiated NZB.H-2bm12/b F1 mice were reconstituted with T-cell-depleted bone marrow cells from 3- to 6-week-old donors of four different congenic strains, NZB.H-2bm12, NZB.H-2b, B6.C-H-2bm12 and C57BL/6 (H-2b) mice. All animals when then serially followed for the appearance of IgM and IgG anti-ss and dsDNA antibodies. Significant alterations of T-cell subsets, high levels of IgG anti-dsDNA antibodies and proteinuria were found only in recipient NZB.H-2bm12/b F1 mice that were reconstituted with T-cell-depleted NZB.H-2bm12 bone marrow cells. Such activity was not found in F1 mice engrafted and fully reconstituted with NZB.H-2b, B6.C-H-2bm12 or C57BL/6 (H-2b) T-cell depleted bone marrow cells. Additionally, to evaluate the importance of the NZB background (non-H-2) genes, we transferred T-cell-depleted bone marrow cells from NZB.H-2bm12 mice into H-2 compatible B6.C-H-2bm12 mice and vice versa. Without NZB background genes, an increase in CD4- CD8- T cells, IgG anti-dsDNA, splenomegaly, and proteinuria were not observed. These data suggest that the H-2bm12 gene and the NZB background genes in bone marrow-derived cells are both necessary for the altered expression of T-cell subsets and anti-DNA production.(ABSTRACT TRUNCATED AT 250 WORDS)