The importance to practicing nephrologists of lupus nephritis (1–3) is that, although rare, it is a serious disease whose prognosis can usually be improved dramatically by treatment, but for which the treatment is potentially toxic, prolonged, complex, and difficult to plan and carry out. Lupus is defined by its clinical picture, together with antibodies directed against one or more nuclear components, particularly anti-doublestranded DNA (dsDNA). It is best regarded as a syndrome, in which a variety of immunologic events may lead to a similar final common pathway, and thus present a similar clinical picture (4).

One important distortion that occurs through the usual style of reporting of lupus in the literature is that by defining “typical” or “core” patients with a positive antinuclear antibody and/or dsDNA antibodies, a considerable number of patients are excluded who belong to the lupus “family” of diseases, but do not satisfy current strict criteria. These patients are in practice as important to recognize and treat as those with “classical” lupus. Many with a clinical lupus syndrome but a negative antinuclear antibody have low titers of anti-Ro antibody; this subset of patients rarely has significant renal disease, but often has a high incidence of antiphospholipid antibodies and associated thromboses and abortions (see below), as well as inherited complement deficiencies.