Silver stain after isoelectric focusing of unconcentrated cerebrospinal fluid: Visualization of total protein and direct immunofixation of immunoglobulin G

A silver stain technique has been developed to study proteins in unconcentrated cerebrospinal fluid (CSF) after isoelectric focusing. This method is highly sensitive, and bands containing 25 to 50 ng protein can be clearly distinguished, so that small volumes (40 μl maximum) of native CSF can be used. Individual proteins (e. g., immunoglobulin G) can be detected easily by specific immunofixation. It is also possible to perform direct precipitation and direct specific immunofixation on a single gel in order to compare side by side the patterns of the whole and of specific proteins from different samples of CSF. The technique is simple and highly reproducible, and results are obtained 6 h after sample deposition (if immunofixation is used, a further 24 h washing is necessary). The sensitivity and versatility of this technique (immunofixation can be applied to the detection of any antigen) should permit its extension to other biological fluids with a low protein content.