The characterization of human anti-IgG autoantibodies by liquid isoelectric focussing.

A series of human anti-IgG autoantibodies (AGA) have been analyzed by liquid isoelectric focusing in order to a) determine their isoelectric points (pI) and b) assess their heterogeneity. The 13 AGA examined include five IgM, five IgA, and three three IgG AGA. All demonstrate a single major peak indicative of restricted heterogeneity and each is characterized by an acidic pI. This anodal pI is distinct from other immunoglobulins isolated from the same serum that do not exhibit anti-IgG activity. It is speculated that the acidic pI is the result of acidic amino acid substitutions in the variable regions of immunoglobulin chains. The restricted heterogeneity and distinctive pI of the AGA suggest the selection of structurally similar antibody molecules from the large repertoire available in the human genome.