Proteolytic cleavage of human IgG molecules by neutral proteases of polymorphonuclear leukocytes

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Abstract
The effect on human IgG of the elastase-like (ELP) and chymotrypsin-like (CLP) neutral proteases derived from human polymorphonuclear leukocytes was studied. By incubating ELP with monoclonal IgG proteins, two immunochemically and electrophoretically distinct components were formed which were similar, but not identical, to the Fc and Fab fragments produced by papain digestion. When an IgG protein was incubated under similar conditions with the CLP enzyme, no proteolysis was observed. IgG proteins differed in their susceptibility to proteolysis by ELP. These differences were related to the subclasses IgG1-IgG4. The IgG1 and IgG3 proteins were readily cleaved by ELP, but the IgG2 and IgG4 proteins were more resistant. Although free light chains differ in susceptibility to proteolysis by ELP, our studies showed that neither the type (K or λ) nor the subgroup of light chain affected the susceptibility of complete IgG molecules to cleavage by this enzyme.