Direct evidence of a heterotrimeric complex of human interleukin-4 with its receptors.

The mode of binding of interleukin-4 (IL-4) to its two known receptors, specific receptor IL-4R and a shared receptor gamma c, was investigated using gel filtration and gel electrophoresis. A ternary complex between IL-4 and the soluble domains of the two receptors was shown to exist in solution. The association constant between gamma c and the stable complex of IL-4/sIL-4R is in the millimolar range, making the ternary complex a feasible target for crystallization studies.