Competitive Inhibition of Reagin-Mediated Histamine Release by a Human IgG2 Myeloma Protein

Abstract

Two human IgG myeloma proteins were isolated from other serum proteins based upon their fixation to monkey lung tissue. Electrophoretic and subclass studies revealed that the slow (<i>γ</i><sub>2</sub>) migrating protein belonged to the IgG1 subclass, and the fast (<i>γ</i><sub>1</sub>) migrating protein belonged to the IgG2 subclass. Competition experiments showed that the IgG2 myeloma protein competes for the same tissue-binding sites as human reagin. In addition, the IgG2 myeloma protein (1) loses its tissue-binding properties upon heating at 56 °C and treatment with mercaptoethanol, (2) gives reverse histamine release from monkey lung tissue challenged with rhesus antihuman IgG, and (3) fixes to monkey skin for at least 3 days. On the other hand, the IgG1 myeloma protein does not compete with human reagin for tissue-binding sites but apparently binds at separate, distinct receptor sites on monkey lung tissue.