Kinetics of the Different Susceptibilities of the Four Human Immunoglobulin G Subclasses to Proteolysis by Human Lysosomal Elastase

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Abstract
Human lysosomal elastase cleaves human monoclonal Ig[immunoglobulin]G into components that closely resemble the fragments produced by papain digestion. IgG1 produced Fab, Fc and Fab-Fc fragments; cleavage of IgG2 produced F(ab)2, Fab-Fc, Fab and Fc fragments; IgG3 gave rise to almost pure Fab and Fch (Fc covalently joined to the extended hinge region polypeptide to IgG3); from IgG4, F(ab)2, Fab and Fc fragments were recovered. The relative susceptibilities of the 4 human IgG subclasses to proteolytic attack by elastase were studied kinetically and showed the following decreasing order of susceptibility: IgG3 > IgG1 > IgG2 > IgG4. The Fab fragment from papain digestion of IgG1 and the corresponding fragment from elastase digestion showed indistinguishable MW and immunochemical identity.