Solid-phase immunofluorometric assay for quantification of CSF immunoglobulins. Determination of normal reference...

Because a highly sensitive method is required to quantify low concentrations of immunoglobulin (Ig) classes in cerebrospinal fluid (CSF), there have been a few papers reporting normal values of CSF IgG, IgA and IgM determined in the same samples. Enzyme immunoassay (EIA) is most frequently used, but has such drawbacks as susceptibility of enzyme to inhibition and denaturation and the requirement for additional incubation with a substrate. Therefore, solid-phase immunofluorometric assay was evaluated for quantification of CSF IgG, IgA and IgM in the nanogram range. We found this to be rapid and reproducible. The mean (SD) values of normal CSF samples obtained from 22 subjects with tension headache were 23.9 (7.6) micrograms/ml for IgG, 2.00 (0.90) microgram/ml for IgA and 197 (87) ng/ml for IgM. The normal mean (SD) values of indexes were 0.51 (0.10) for IgG, 0.25 (0.05) for IgA and 0.044 (0.017) for IgM. These values agreed quite well with those determined by EIA. The values of CSF albumin correlated significantly with those of CSF IgG or IgA, but did not with those of CSF IgM. Levels of each of the three Ig classes in CSF and serum were significantly correlated. When CSF/serum ratio was introduced, a significant correlation between the albumin ratio and each Ig ratio was found. These results suggest that the Ig content of normal CSF may depend upon that of serum and upon the characteristics of the Ig molecule.