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Interstitial immune complex nephritis in patients with systemic lupus erythematosus (SLE). Renal tissues from 45 patients with SLE nephritis, 34 patients with idiopathic membranous nephropathy (IMN) and 77 patients with minimal glomerular disease (MGD) were studied by light, immunofluorescence and electron microscopy. Interstitial nephritis characterized by focal or diffuse infiltration of inflammatory cells, tubular damage and interstitial fibrosis was observed in 66% of SLE patients. Fluorescein-conjugated antibodies to immunoglobulins or complement or both were bound to peritubular capillaries, interstitium and tubular basement membranes (TBM) in 53% of patients with a granular pattern corresponding to opaque deposits seen by light or electron microscopy or both. Antibodies reactive with thymidine or cytosine or both were bound to interstitial structures in 19% of patients tested and showed the same granular distribution. Interstitial cellular infiltration was rare and deposits of immunoglobulins and complement were rare or absent in IMN and MGD, whereas deposits of DNA products were never observed. The findings are consistent with the interpretation that in patients with SLE nephritis immune deposits, presumably containing DNA-anti-DNA complexes, localize in peritublular capillaries, TBM and interstitum, thereby producing an inflammatory reaction which contributes to development and evolution of renal diseases.

Light and ultrastructural features of a cerebellar hemangioblastoma in a 56-year-old man are described in detail. The neoplasm was composed of three major cell types: endothelial cells, pericytes, and stromal cells. The endothelial cells lined the fenestrated vascular channels. The pericytes were ensheathed by their own basal lamina which separated them from the basal lamina covering the endothelium. The stromal cells contained, in addition to the conventional organelles, numerous membrane-bound lipid inclusions, annulate lamellae, and nuclear bodies. There were also present transitional cells which shared the fine structure of all the three major cell types. Histogenetically, the tumor was considered to be of vascular origin. The stromal cells represented the stem cells which, under the neoplastic influence, continued to proliferate and differentiate into "vasoformative" elements (pericytes and endothelium) which formed new blood vessels. The transitional forms between the stromal cells and the "vasoformative" elements suggested that the cellular components of a hemangioblastoma shared a common ancestry, most likely of an angioblastic lineage.