Oligoclonal Bands: Isoelectric Focusing and Immunoblotting, and Determination of κ Free Light Chains in the Cerebrospinal Fluid

Abstract

A variety of inflammatory diseases of the central nervous system ranging from an autoimmune to infectious pathophysiology are characterized by intrathecal B cell activity. Immunoglobulins (Ig) and free light chains (FLC) which are both secreted by terminally differentiated B cells can be detected in the cerebrospinal fluid (CSF). As these proteins are not only present in the CSF in case of intrathecal inflammation, but also derive from blood by diffusion across the blood–CSF barrier, methods for the detection of an intrathecal synthesis needs to take this into account. For the determination of an intrathecal IgG synthesis, isoelectric focusing followed by immunoblotting is the gold standard. This technique reveals oligoclonal bands (OCB) and depends on comparing paired CSF and blood samples of each individual patient. An intrathecal IgG synthesis is present if OCB are detected in CSF without corresponding bands in serum. For the determination of an intrathecal κ-FLC synthesis, first κ-FLC concentrations are measured in CSF and serum, usually by nephelometry using antibodies against κ-FLC-specific epitopes, and then referred to an upper normal limit. For this comparison, different approaches can be applied, among others the calculation of the κ-FLC index. In this chapter, we provide background information on OCB and κ-FLC, describe the technology used for their determination, discuss their applications in clinical practice and how to interpret the obtained results.