Immunoreactivities of amyloid beta peptide((1-42)) (Abeta42-IR) and total tau protein (TTIR) were measured in lumbar cerebrospinal fluid of 48 patients (12 patients in each group) with normal pressure hydrocephalus (NPH), vascular dementia (VD), Alzheimer's disease (AD), Parkinson's disease without dementia (PD) and 24 controls (CON) using sensitive and specific enzyme immunoassays. TTIR in NPH was not significantly changed compared with VD, PD and CON, while NPH-Abeta42-IR was significantly decreased compared with PD and CON. In AD, significant increases of TTIR and significant decreases of Abeta42-IR were found. Using a TTIR by Abeta42 plot, all NPH, PD, and CON samples were within the non-AD plot region. 92% of AD and VD samples were within the AD and non-AD area, respectively. We conclude that combined measurement of Abeta42-IR and TTIR contributes to the differential diagnosis of NPH vs. AD and of AD vs. VD, respectively.

Immunoreactivities of total apolipoprotein E (ApoE-IR), amyloid beta peptide(1-42) (Abeta42-IR), interleukin-6 (IL-6-IR), substance P (SPIR) and total tau protein (TTIR) were measured in lumbar cerebrospinal fluid samples of patients with Alzheimer's disease (AD), non-Alzheimer's dementias (NAD), neurological disorders without cognitive impairment (OND) and controls without central nervous system disease using sensitive and specific enzyme immunoassay methods. TTIR was highly significantly increased (P < 0,001) and Abeta42-IR was significantly decreased (P < 0,001 vs. OND/CO, P < 0,03 vs. NAD) in the AD cohort compared with the other diagnostic groups. Significant increases in AD were also found for ApoE-IR (P < 0,001) and IL-6 (P < 0,03), but there was a considerable overlap between groups. In the total AD cohort, SPIR was not significantly changed, but AD patients with late disease onset (>65 years) showed significantly higher values than both early onset patients (<65 years) and controls (P < 0,05). Discriminant function analysis showed that Abeta42-IR (cut-off value 375pg/ml) and TTIR (cut-off value 440 pg/ml) levels contributed most to the group classification of patients. At 85% sensitivity for AD and 100% specificity for controls, the combined evaluation of Abeta42-IR and TTIR in this cross-sectional study resulted in a graph separating AD from non-AD patients with increased specificity of 91% and 75% for AD versus OND and NAD, respectively.

We conclude that elevations of CSF IL-6-IR can not serve as a diagnostic marker of the disease, but, hypothetically, could reflect presence or activity of IL-6 mediated immunological phenomena in single AD patients.

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Using a specific enzyme linked immunosorbent assay (ELISA) method, total apolipoprotein E immunoreactivity (tApoE-