Cleavage of human IgM with human lysosomal elastase

Human lysosomal elastase, a serine proteinase stored in the azurophil granules of polymorphonuclear leucocytes, cleaves human monoclonal IgM producing two fragments and dialyzable peptides. An F(ab)₂μ-like fragment, called IgMe in this report, retains some reactivity with an anti-Fcμ-antiserum and is antigenically deficient with respect to both the subunit (IgMs) produced by reduction and alkylation of IgM and the similar fragment (IgMp) produced by papain digestion. The other fragment is very similar to Fabμ generated by papain digestion, as indicated by immunochemical identity and a similar molecular weight.