Binding of cytokines to pharmaceutically prepared human immunoglobulin

Abstract

Pharmaceutically prepared IgG, pooled from sera of over 2,000 normal individuals, contained both monomeric and dimeric IgG. Each type of IgG bound 125I-labeled interleukin (IL)-1α, IL-1β, IL-6, and tumor necrosis factor (TNF)-α. Increased binding to IgG was observed if 125I-1L-1β was denatured by heating to 39°C. However, the binding of both nondenatured and denatured 125I-IL-1β was not inhibited by unlabeled IL-1β. In contrast, binding of 125I-IL-1α, 125I-IL-6, and 125I-TNFα was inhibited by the corresponding unlabeled cytokine. Papain-digestion of IgG abolished binding of 125I-TNFα but failed to influence the displaceable binding of 125I-IL-1α and 125I-IL-6. 125I-TNFα was a mixture of trimeric and monomeric forms, the latter being the predominant form at lower concentrations. The apparent saturability of 125I-TNFα was explained by a higher nonspecific binding of monomeric than of trimeric 125I-TNFα to IgG. The amounts of cytokine antibodies in IgG preparations would contribute ∼ 2 μg anti-IL-1αa IgG and 1 μg anti-IL-6 IgG per kg body wt during high dose immune globulin therapy. In conclusion, pharmaceutical preparations of human IgG contain specific and neutralizing, high affinity antibodies against IL-1α and IL-6, but not against TNFα or IL-1β. There are significant methodological pitfalls that hamper detection of IgG autoantibodies against cytokines.