Molecular heterogeneity, detected by two electrophoretic micro procedures, of IgG in human cerebrospinal fluid (CSF)

Semi-automated electrophoretic procedures in the PhastSystem (Amersham Pharmacia Biotech) with micro polyacrylamide gels (PAGs) and SDS-PAG gradients were modified to analyze IgG in human cerebrospinal fluid (CSF) and matched serum samples with respect to the molecular IgG structure L-H-H-L. Isoelectric focusing (IEF) with specific immunofixation detected discrete IgG bands in CSF standing out against a polyclonal and monoclonal background pattern in CSF and serum; they were denoted oligoclonal bands (IgG OBs) (OB assay positive) indicating IgG synthesis in the central nervous system (CNS) of patients with subacute and chronic processes of inflammatory CNS disorders; assay was negative with identical (mirror) bands in CSF and serum for other CNS processes. IgG OBs were specified as lambda (kappa) IgG subfractions, precipitated with the anti-light (L) chains lambda (kappa) and anti-heavy (H) chain fragments (Fd, Fc, C(H)2) as well as with anti-F(ab')(2), and as duplex IgGs with kappa and lambda OBs at the same pI. With SDS-PAG gradient electrophoresis and specific immunofixation more than six IgG fractions were detected and classed according to apparent molecular weights of a S-sulfonated human IgG standard; they were characterized with the monospecific antibodies against the L and H chain fragments as 25, 50, 75, 100, 125 and 150 kD fractions containing combinations of L and H chains as well as mixtures of both L and H chain fragments of varying dimensions. Generally, this molecular IgG heterogeneity could not be connected with the IgG OB heterogeneity revealed by IEF; but single OBs in the strongly alkaline pH region of PAG may correspond to H fragments with basic pI. Nevertheless, evidence for the existence of both free L chains and the free H chain were revealed as specific OBs with IEF and with the anti-L and anti-H antibodies in the 25 kD and 50 kD fractions, respectively, of CSF samples of six patients with diverse CNS diseases. Further experiments are needed to elicit the origin of the molecular IgG heterogeneity during the immune response of subacute and chronic inflammatory processes in human CNS.