Isoelectric focusing of unconcentrated cerebrospinal fluid: Applications to ultrasensitive analysis of oligoclonal immunoglobulin G

The application of isoelectric focusing (IEF), immunoglobulin G (IgG) immunofixation and silver staining for the analyses of unconcentrated cerebrospinal fluids (CSF) and sera are described. We have standardized these methods, and applied them to IgG oligoclonal band analysis. The sensitivity of the procedure was 0.3 μg IgG. Optimum results were obtained with 0.5 μg IgG in 5–20 μl application volumes. Equal quantities of CSF and serum IgG analyzed by IEF in 55 normal individuals showed comparable intensities and isoelectric points and of these, four individuals (8%) had bands in CSF which were not detectable in serum. The CSF and sera from patients with multiple sclerosis, subacute sclerosing panencephalitis, Huntington's disease and Guillain‐Barré syndrome were also examined. Pathologic banding patterns can be classified into three categories: Bands present (1) exclusively in CSF, (2) more intense in CSF compared to serum, and (3) equally intense in CSF and serum. Oligoclonal IgG bands are defined as bands found exclusively or more intense in CSF compared to serum, and are indicative of intra‐blood‐brain‐barrier IgG synthesis.