Identification of human IgG autoantibodies specific for IL-10

Since autoantibodies to IL-1α, interferon-alpha (IFN-α) and IL-6 have been described, this study concentrated on the search for autoantibodies to hIL-10 using an assay based on the precipitation of ¹²⁵I-hIL-10 anti-IL-10 autoantibody complexes using Protein G-Sepharose. Among 1860 tested sera, only seven were found to specifically precipitate IL-10, thus indicating the rare occurrence of such autoantibodies. Four of those seven anti-IL-10 autoantibody sera were specific for hIL-10, two recognized both human and viral IL-10, while the last one recognized human, viral and murine IL-10, thus suggesting the existence of at least three different epitopic specificities. The purification of anti-IL-10 autoantibody from one serum demonstrated the existence of a single (IgG1, λ) autoantibody that neutralized IL-10 biological activity. Thus, autoantibodies to IL-10 may represent natural antagonists to IL-10.