Tissues obtained from 34 human renal allografts by biopsy, 1 to 31 months after transplantation, were studied by histologic, immunofluorescence, and immunoferritin techniques. Our purpose was to gain more precise information concerning the localization of immunoglobulins and complement in glomeruli and to describe the associated tubular and vascular changes.
Localization of fluorescein-labeled antibodies (Fl-Abs) to IgG, IgM, β1C, and C′1q was seen in glomeruli from 25 allografts and showed the following distribution of patterns: (a) diffuse linear, four; (b) diffuse granular, four; (c) focal linear, six; (d) focal granular, six; and (e) indeterminate, five. Ferritin-conjugated antibodies (Fer-Abs) localized in 21 allografts. Electron microscopic findings correlated with the foregoing immunofluorescence patterns. (a) Fer-Abs were bound on the endothelial side of the glomerular basement membrane and in the subendothelial space. (b) Fer-Abs were bound in subendothelial and subepithelial deposits similar to those seen in experimental acute or chronic serum sickness. (c and d) Fer-Abs were seen in the subendothelial space and mesangial matrix. Deposits were present in these areas and some bound Fer-Abs. The two groups were not readily separable on the basis of immunopathologic data. (e) Fer-Abs were mostly seen in the mesangial area.
Nine allografts displaying little or no binding of Fl-Abs failed to bind Fer-Abs.
Small amounts of fibrinogen were found in only six allografts, three of which showed diffuse granular fluorescence.
In 12 allografts either Fl-Abs or Fer-Abs or both were bound in walls of blood vessels. The position of these reactants was in foreign deposits and in basement membranes of arteries and veins.
The immunopathologic findings seem to support best the hypothesis that damage to allografts is associated with deposition, in glomerular and vascular structures, of circulating antigen-antibody complexes which might contain, in part, transplantation antigens.