Labeling of cerebral amyloid in vivo with a monoclonal antibody

Abstract

We assessed the ability of a murine monoclonal antibody to bind selectively to beta-amyloid in the brains of living nonhuman primates. To circumvent the blood-brain barrier, we injected unlabeled antibody 10D5 (murine whole IgG1 and/or Fab fragments) into the cerebrospinal fluid of the cisterna magna in three aged monkeys. A control animal was given an intracisternal injection of nonimmune mouse whole IgG plus Fab. Twenty-four hours later, the animals were perfused and prepared for immunohistochemical detection of bound murine immunoglobulin in brain. All three experimental animals showed selective binding of 10D5 to approximately 5-15% of amyloid deposits in cerebral cortex, primarily near the cortical surface. There was no labeling in the control animal. In vivo-labeled deposits were confirmed to be beta-amyloid by electron microscopy and by in vitro immunohistochemistry in adjacent sections. The animals tolerated the injection well, although some polymorphonuclear leukocytes infiltrated portions of the subarachnoid space and superficial neocortex. These results provide the first demonstration that it may be feasible to selectively direct a tagged monoclonal antibody to beta-amyloid in the brain for therapeutic or diagnostic purposes. With enhancement of labeling efficiency, the method also may be useful for studying the progression of beta-amyloidosis in experimental animals using emission tomography.

Figure 1.

Adjacent immunostained sections of frontal neocortex from the 34-year-old rhesus monkey showing in vivo-labeled Aβ (A) and in vitro-labeled Aβ (B). Note that in vivo labeling is relatively light and is restricted to a band of deposits near the cortical surface (arrows indicate surface). Bar = 200 μm.

Figure 2.

Aβ deposits in adjacent, in vitro- and in vivo-immunostained sections from the 18-year-old squirrel monkey (A, B) and the 34-year-old rhesus monkey (C, D). Deposits in A and C were stained by in vitro application of 10D5; B and D show the same deposits labeled by in vivo antibody in an adjacent section. Bars = 20 μm.

Figure 3.

High-resolution analysis of in vivo-labeled Aβ deposits in the 34-year-old rhesus monkey. A-C: In vivo-labeled plaque-like deposit at successively higher magnifications; arrow indicates the lightly labeled core, arrowhead indicates a collection of heavily labeled peripheral Aβ fibrils. A. Light micrograph of plaque in a 1-μm-thick section, toluidine blue counterstain. Bar = 10 μm. B. Low-magnification electron micrograph of plaque in A. C. High-magnification electron micrograph showing amyloid fibrils in a portion of the plaque core. D. Electron micrograph showing DAB-encrusted Aβ fibrils from another in vivo-labeled plaque. Bar = 0.5 μm.

Figure 4.

Schematic diagrams of in vitro- (A) and in vivo-immunolabeled (B) Aβ deposits in rostral telencephalon of the 18-year-old squirrel monkey. Note that in vivo-labeled deposits occur in superficial neocortex, primarily along the ventral surface of the brain. V Lat = lateral ventricles.

Figure 5.

Schematic diagrams of in vitro- (A) and in vivo-immunolabeled (B) Aβ deposits in prefrontal cortex of the 34-year-old rhesus monkey. The percentage of in vivo-labeled deposits was somewhat greater in the rhesus monkey than in the 18-year-old squirrel monkey. CS = cingulate sulcus; PS = principal sulcus.