Immunologic dysfunction: simultaneous study of Alzheimer's and older Down's patients.

Peripheral blood lymphocytes from Alzheimer's disease patients, older patients (aged 25-59 years) with Down's syndrome and closely age-matched healthy controls were tested in vitro for DNA synthesis in response to stimulation by phytohemagglutinin, pokeweed mitogen and OKT3 monoclonal antibody to T3 antigen. All were significantly decreased in Down's and Alzheimer's patients relative to healthy controls. The autologous mixed lymphocyte reaction (AMLR), unstimulated or stimulated with anti-T3. in the 2 patient groups did not differ significantly from the healthy controls. We also quantified the proportions of the T cells staining positive for surface membrane orosomucoid, and found their levels to be either higher or lower than normal in Down's patients, but not in Alzheimer's patients. These results demonstrate the existence of defective cellular immune functions in both elderly Down's patients and Alzheimer's patients.