Immunohistochemical staining of senile plaques.

Immunohistochemical staining of serum proteins, including immunoglobulins, was carried out on formalin-fixed cerebral tissue from 24 autopsy cases (twenty dements, four controls) and fifteen biopsy cases (ten dements, five controls). Sixteen of the autopsy cases showed focal regions where there was staining of globulins and other serum proteins within senile plaque 'cores', nerve cell perikarya and astrocytes. This pattern of staining, generally, occurred either in relation to areas of cerebral infarction or in the neighbourhood of small arteries displaying arteriosclerotic changes. In tissue areas, distant from these vascular alterations, no staining occurred. Furthermore, none of the biopsy cases showed any such areas of staining. These findings indicate that the positive immunohistochemical reactions demonstrated within senile plaques (and other tissue components) are more likely to result from leakage of serum proteins, including immunoglobulins out of damaged vessels and into the brain parenchyma, rather than being indicative of the involvement of immunological mechanisms in the aetiology of plaques, as has been suggested by other workers.