Cloning of a human IgM autoantibody bearing a cross-reactive idiotype in a lambda expression vector: a new approach to studying autoantibodies

Abstract

The monoclonal antibody 4B4 is a human IgM,kappa which expresses a cross-reactive lupus-associated idiotype and has anti-Sm binding activity. We find that the VL nucleotide sequence of 4B4, like the 4B4 VH region, is encoded by unmutated germline genes. The 4B4 VH and VL were cloned into the ImmunoZap lambda expression vector to produce three recombinant immunoglobulin polypeptides. These recombinant polypeptides expressed, respectively, either the 4B4 VH or VL alone or a VH/VL heterodimer. ELISA showed that the VH/VL heterodimer retained anti-Sm antibody activity. The 4B4 idiotype was found predominantly on the VH. This report describes: (i) a method for producing recombinant immunoglobulin molecules from an IgM-secreting B cell line and (ii) the ability of recombinant antibody fragments expressed in Escherichia coli to retain the structural and antigenic properties of the native molecule.