Slowly Sedimenting Mercaptoethanol-resistant Antinuclear Factors Related Antigenically to M Immunoglobulins (γ1M-Globulin) in Patients with Systemic Lupus Erythematosus *

Abstract

The human immunoglobulins currently recog- nized can be divided into three major classes: the 7 S y2-globulins (G immunoglobulins, IgG); the ylM-globulins (M immunoglobulins, IgM); and the 'ylA-globulins (A immunoglobulins, IgA) 1 (2). These proteins can be readily distinguished from each other with specific antisera directed against the antigenic determinants associated with the heavy chains characteristic of each class. In addition, M immunoglobulins have a sedimentation coefficient of 19 S (mol wt of about 1,000,000), and their antibody activity is destroyed by treat- ment with 2-mercaptoethanol or other thiol com- pounds, whereas G immunoglobulins have a sedi- mentation coefficient of 7 S (mol wt of about 160,-000), and their antibody activity is not significantly affected by treatment with thiol compounds. Most A immunoglobulins sediment with the IgG