Isoelectric focusing description

The most characteristic abnormality in patients with multiple sclerosis is certainly the intrathecal synthesis of IgG. It can be demonstrated—with different sensitivity— by various methods, which can be divided into qualitative and quantitative methods. The gold standard for the demonstration of intrathecal synthesis of IgG is the detection of oligoclonal bands, which are not present in CSF, in the appropriately diluted serum (i.e., to the same concentration of IgG) by isoelectric focusing. This is a qualitative method and the description of its different modifications and interpretations goes beyond the scope of this chapter. This method is by far the most sensitive, and its sensitivity is reported between 90 and 100%. Here it is suitable to repeat that the detection of plasmocytic forms in cerebrospinal fluid may also be regarded as qualitative proof of intrathecal synthesis of immunoglobulins— although in this case the proof is obviously not specific for IgG from the theoretical point of view. 

Isoelectric focusing was developed to separate proteins on the basis of differences in their pi values. The mechanism of IEF can be treated mathematically and the classical analysis is presented in the Appendix. On the other hand, the mechanism of IEF is relatively easy to conceptualize and lends itself to a simple description. The historical, theoretical, and practical aspects of IEF are well documented. Many experimental details can be found in several monographs and review articles.1,2,8-17 Refs. 1 and 2 are particularly recommended. They provide valuable insights from one of the pioneers in the field. 

The five major formats of the CE experiment are capillary zone electrophoresis (CZE), micellar electrokinetic chromatography (MEKC), capillary gel electrophoresis (CGE), capillary isoelectric focusing (CIEF) and capillary iso-tachophoresis (CITP). The following gives a brief description of the mode of separation, and some examples of analyses which can be performed employing such separation strategies. 

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