CSF in Alzheimer's disease. Studies on blood-brain barrier function and intrathecal protein synthesis

Serum and cerebrospinal fluid (CSF) from 22 ambulatory and 10 institutionalised patients with Alzheimer's disease (AD) and 22 age-matched controls were assayed nephelometrically for concentrations of IgG, IgA, IgM, haptoglobin, transferrin, prealbumin and albumin. The CSF/serum ratio and index were calculated for each protein. In the CSF of ambulatory patients IgG, transferrin and albumin were elevated while the institutionalised patients had higher IgG and IgA levels compared to the controls. The CSF haptoglobin was elevated in institutionalised AD patients compared to those who were ambulatory. The CSF/serum ratio for albumin was elevated in both groups. An increase in the IgG ratio was also found in both groups. The ratios for haptoglobin and prealbumin were markedly increased in the institutionalised patients. CSF indices gave no evidence for increased intrathecal synthesis of any of the proteins investigated. The increased CSF/serum ratios for IgG and albumin and also the higher CSF albumin in patients with AD suggest an increased blood-brain barrier permeability in this disease. The high prealbumin ratio may be related to amyloidogenesis often present in AD.