IgG Autoantibodies against Interleukin 1α in Sera of Normal Individuals

Abstract

A pool of human sera from healthy blood donors was found to interfere competitively with the binding of ¹²⁵I-labelled human recombinant interleukin 1α (rIL-1α) to the murine T-cell line EL4. The interference was reversible at the cellular level, and direct binding of the ligand to serum factors was therefore investigated. After preincubation of [¹²⁵I]rIL-1α with pooled serum, the ¹²⁵I activity eluted in two peaks from a Sephadex G-75 column. The first was located in the void volume. The second eluted together with monomer rIL-1α. An almost complete displacement of the high molecular weight ¹²⁵I fraction was achieved with an excess of unlabelled rIL-1α but not with rIL-1β. The serum factors binding to [¹²⁵I]rIL-1α were located in the molecular weight range 100,000–200,000, judged by fractionation on a Sephacryl S-400 column, and the factors were bound to immobilized protein A. Furthermore, [¹²⁵I]rIL-1α preincubated with serum co-precipitated with a specific rabbit anti-human IgG antibody. Screening of 29 sera from normal individuals showed similar effects in three cases. We conclude that approximately 10% of normal human sera contains detectable IgG autoantibodies to IL-1α.