Presence of Immunoglobulins and Complements in the Amyloid Plaques in the Brain of Patients with Alzheimer’s Disease

Summary

The presence of immunoglobulins and complement factors in the amyloid in senile plaques in the brain of six patients with Alzheimer’s disease has been demonstrated by means of immunofluorescence, immunoperoxidase, or the avitin-biotin complex immunoperoxidase (ABC) method.

A positive immunohistochemical reaction of senile plaques was noted with anti-IgG antibody. Not all the senile plaques showed the positive reaction to anti-IgG antibody. The reason for the negative reactions is not known, but antigenic sites of immunoglobulins were probably partially masked by the subsequent activation of complement cascades. Immunohistochemistry revealed that the complements C1q, C4, and C3 were on the amyloid fibrils of senile plaques, but results for complements C5–C9 were consistently negative. Other serum components such as albumin, prealbumin, IgA, IgM, CRP (C-reactive protein), and β₂-microglobulin were not found in the amyloid of senile plaques, nor were other factors related to the immunological response of the central nervous system such as HLA, B cells, OKB2, granulocytes, leukocytes, or fibronectin.

If the presence of C1q and C3 in the amyloid of senile plaques is an immune reaction triggered by an immune complex, this might explain the tissue damage surrounding the amyloid fibrils, i.e., the senile plaque formation.