A comparative analysis on clinicopathological and immunohistological characteristics was performed of 205 cases with primary IgA nephritis and 35 with Schönlein-Henoch purpura nephritis (purpura nephritis). Diagnostic criteria for primary IgA nephritis were set out so that IgA was either the most prominent immunoglobulin or, at least, equal to IgG and/or IgM, if present, irrespective of mesangial or peripheral localization. In primary IgA nephritis, one half of the cases were discovered by asymptomatic proteinuria, and one-third presented recurrent upper respiratory tract infection and gross hematuria, one-fourth abdominal pain and a few cases joint pain, while purpura nephritis was associated with a significantly higher incidence of such systemic symptoms as abdominal and joint pains, in addition to purpura. Both diseases shared a tendency toward conspicuous hematuria in contrast to the modest proteinuria, with normal renal function in three-fourths to two-thirds. Moreover, four of 35 with purpura nephritis showed preceding proteinuria and had been regarded as primary IgA nephritis until purpura appeared. The glomerular pathology had a common feature in that there was frequent occurrence of mesangial proliferative and focal and segmental lesions. The immunohistology in the two diseases was indistinguishable with regard to the glomerular immunoglobulins and mediators, whether purpura was present or absent. Thus, we propose a unifying concept that, by analogy with SLE, primary IgA nephritis may be regarded as‘sine lupo,’lying on one side of the nosological spectrum with less systemic symptoms, whereas purpura nephritis may occupy the other side with more systemic aspects. Furthermore, we confirmed the epimembranous granular deposition of IgA in both diseases as the most characteristic morphological expression of circulating immune compl
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