A mechanism for sustained production of pathogenic autoantibody subsets in patients and mice with systemic lupus erythematosus may be centered on selective up-regulation of B cells bearing certain idiotypes. Public idiotypes are characteristic of some autoantibodies, including anti-DNA. Evidence is reviewed that suggests that immunoglobulins bearing certain public idiotypes, such as IdGN2, contain autoantibody subsets that are nephritogenic in human systemic lupus erythematosus and in New Zealand black/New Zealand white F1 mice. Up-regulation of such cells could promote development of nephritis. Work from several laboratories has shown that production of immunoglobulin G antibodies to DNA depends upon T cell help. In New Zealand black/New Zealand white F1 mice, cloned T cells are dominated by autoreactive cells that produce B cell growth factors. We suggest that this sustained release of B cell growth factors combined with selection by T helper cells for B cells bearing IdGN2 are a major mechanism for sustained up-regulation of nephritogenic subsets of autoantibodies.