In vitro production of a biologically active Fab 2-like fragment by digestion of human IgM rheumatoid factor with human polymorphonuclear leukocyte elastase

Abstract

Experiments were performed to determine if IgM rheumatoid factors (RF) are digested by human polymorphonuclear leukocyte (PMN) elastase in a manner similar to other IgM proteins. As with the non-RF IgM(San), a fragment (P-fragment) with an estimated molecular weight of 120,000 daltons is produced by elastase digestion of IgM RF (Pom). Ouchterlony analysis with Fd- and IgM-specific antlsera demonstrated that P-fragment is Identical to the Fab 2-like fragment (Fragment A′) from elastase digestion of IgM (San). P-fragment agglutinates IgG-sensitized sheep erthrocytes in a modified Waaler-Rose assay. Taken together, those findings suggest that P-fragment represents a biologically active Fab 2 fragment.