BALB/c mice injected at birth with 10(8) semi-allogeneic (C57BL/6 x BALB.IgHb)F1 spleen cells develop a lupus-like syndrome in which autoantibodies bear exclusively the donor allotype. We have analyzed the evolution of donor B cell chimerism and the autoimmune manifestations during the first year of life in these mice. Anti-DNA, -histone, and -cardiolipin IgG antibodies as well as circulating immune complexes appeared in the second week of life, reached the highest values around the sixth week, and then progressively dropped to normal values after the sixth month in most mice. The kinetics of the evolution of the autoimmune manifestations, as well as the kinetics of serum donor Ig allotype, were parallel to the kinetics of donor B cell chimerism, which was particularly prominent in the spleens in early weeks of life, and progressively decreased after remission of the autoimmune syndrome. Membrane-proliferative glomerulonephritis, which was followed as the more representative histological abnormality in this model, was particularly evident after 10 weeks of life, but disappeared by the end of the follow-up. Interestingly, when mice with a self-limited disease were re-injected with 10(8) F1 spleen cells i.v., a flare in the serological manifestations was observed. In these re-injected mice a predominance of anti-DNA, IgG1 antibodies bearing exclusively the donor allotype was also observed, as in the early weeks of life.(ABSTRACT TRUNCATED AT 250 WORDS)