Human Interleukin‐3 inhibits the binding of granulocyte‐macrophage colony‐stimulating factor and interleukin‐5 to basophils and strongly enhances their functional activity

Abstract

The human T cell-derived cytokines interleukin (IL)-3, granulocyte-macrophage colony-stimulating factor (CM-CSF), and IL-5 were examined for their ability to bind specifically to human basophils and to regulate their function. Scatchard analysis of equilibrium binding studies showed that IL-3 and GM-CSF, bound to basophils with apparent dissociation constants (K_D) = 8 × 10⁻¹¹M and 3.9 × 10⁻¹¹M, respectively. Specificity studies under conditions that prevent receptor internalization showed that the binding of IL-3, GM-CSF, and IL-5 was not inhibited by tumor necrosis factor (TNF)-α, IL-1β, interferon (IFN)-γ, or G-CSF. However, receptors for IL-3, GM-CSF, and IL-5 interacted with each other on the basophil membrane, showing a unique spectrum of cross-reactivity, with IL-3 competing for GM-CSF and IL-5 binding, whereas GM-CSF and IL-5 showed little or no competition for IL-3 binding. In order to relate the binding properties of these cytokines to function, they were tested for their ability to influence basophil histamine release in an IgE/anti-IgE-dependent system. We found a hierarchy in the stimulation of basophil with the order of potency being IL-3 >GM-CSF >IL-5. In addition, IL-3 stimulated larger amounts of histamine release than GM-CSF or IL-5. The observation that IL-3 interacts with receptors for GM-CSF and IL-5 may have a bearing on its stronger functional effects and suggests a major role for IL-3 in the pathogenesis of hypersensitivity syndromes.