Detection of oligoclonal bands in the cerebrospinal fluid and serum
The clinical diagnosis of multiple sclerosis can be supported by analysis of cerebrospinal fluid (CSF). In a very high proportion of patients with multiple sclerosis (>90%) the CSF contains oligoclonal bands that are not present in the serum. Oligoclonal bands are IgG immunoglobulins secreted by plasma cells that are resident within the CNS in multiple sclerosis. They are secreted into the CSF and can be detected using isoelectric focusing (IEF) in combination with Western blotting. Serum immunoglobulins are also present in low concentration in the CSF and in order to reliably discriminate between locally (CNS) synthesised and systemically synthesised immunoglobulins it is necessary to analyse both serum and CSF collected from a patient at the same time. The oligoclonal bands resolved by IEF are visualized by IgG-specific antibody staining. The detection of CSF oligoclonal bands by isoelectric focusing is not absolutely specific for multiple sclerosis. It reaches its maximal value in the differential diagnosis only when other rare causes of CNS inflammation have been excluded. Isoelectric focusing (IEF) of CSF in agarose gels is followed by passive blotting onto nitrocellulose membrane, followed by immunostaining of IgG by double antibody, using horseradish peroxidase as a visualizing agent. Isoelectric focusing is a method of electrophoresis in a pH gradient established between two electrodes and stabilized by carrier ampholytes. In this technique proteins migrate until they align themselves at their isolelectric point (pI), the point at which a protein possesses no net overall charge and will therefore cease migrating.. It is the electrophoretic technique of choice for detecting CSF immunoglobulin diversity with the highest resolution, in which component that differ by 0.001 of a pH unit can be resolved. For this assay 1ml of CSF and 1ml of serum are required. Smaller volumes can be analysed upon request. The assay is conducted twice a week and results are reported the following day.