Interleukin (IL)-4 plays an important role in IgE synthesis in B cells and in Th2 differentiation in T cells. IL-4 conducts its biological activities through binding to the IL-4 receptor (IL-4R) on the surface of target cells. IL-4R are thought to be composed of the IL-4R a chain (IL-4R alpha) and either the IL-2R gamma chain or the IL-13R cc chain. We have previously shown that the membrane-proximal portion in the cytoplasmic domain of the human IL-4R alpha (hIL-4R alpha) is critical for proliferation, generation of germline epsilon transcript, and activation of STAT6, based on analyses of truncated hIL4R alpha s. In this study, we found that p47(phox), an activator of the phagocyte NADPH oxidase, binds to this portion by the two-hybrid system. Furthermore, we observed the association of p47(phox) with the hIL-4R alpha in B cells derived from a normal donor. These results suggest that p47(phox) is involved in the signal transduction of IL-4 in B cells. However, activation of STAT6, CD23 expression, and IgE synthesis induced by IL-4 were not affected in p47(phox)-deficient patients, which raises the possibility that p47(phox) may be important in other signaling activities as well in B cells. (C) 1999 Elsevier Science Ltd. All rights reserved.
