THE PRIMARY BINDING SUBUNIT OF THE HUMAN INTERLEUKIN-4 RECEPTOR IS ALSO A COMPONENT OF THE INTERLEUKIN-13 RECEPTOR

Interleukin (IL)-13 elicits a subset of the biological activities of t he related IL-4. The basis of this functional similarity is that their specific cell-surface receptors (called IL-13R and IL-4R) are distinc t, yet are complex and share a common subunit(s). The IL-4R primary bi nding subunit (called IL-4R alpha) does not by itself bind IL-13. We s how that the ability of IL-13 to partially compete for IL-4 binding to some human cell types depended on co-expression of IL-4R and IL-13R. However, IL-13 binding was always associated with IL-4 binding. Hypere xpression of IL-4R alpha on cells expressing both IL-4R and IL-13R dec reased their binding affinity for IL-4, abrogated the ability of IL-13 to compete for IL-4 binding, and yet had no effect on IL-13R properti es. Anti-human IL-4R alpha monoclonal antibodies which blocked the bio logical function and binding of IL-4 also blocked the function and bin ding of IL-13. These data show that IL-4R alpha is a secondary compone nt of IL-13R.