Simple Method of Subtyping Human G-Myeloma Proteins based on Sensitivity to Pepsin Digestion

Abstract

HUMAN immunoglobulin G comprises four subclasses called IgG 1, IgG 2, IgG 3 and IgG 4. G-myeloma proteins result from the proliferation of a single clone of plasma cells and belong to only one of the four possible subclasses. At the present time such myeloma proteins represent the only readily available source of subclass specific protein and are increasingly in demand for both immunological investigations and protein sequence analysis. Subtyping of G-myeloma proteins may be achieved by immunological procedures using subclass specific antisera^1,2, by Gm typing³ or by chemical typing⁴. Early work with G-myeloma proteins of the four subclasses revealed striking differences in sensitivity to papain^5,6 and these observations have recently been extended by other groups^7,8 to provide a basis for subtyping. In a recent investigation of the Gm markers associated with the pFc′ fragments of different IgG subclasses⁹, differences were observed between the subclasses in their sensitivity to pepsin digestion and seemed to provide a further tool for subtyping myeloma proteins.