CHARACTERIZATION AND COMPARISON OF THE INTERLEUKIN-13 RECEPTOR WITH THE INTERLEUKIN-4 RECEPTOR ON SEVERAL CELL-TYPES

We describe here the characterization of the interleukin (IL) 13 recep tor and a comparison with the IL-4 receptor on different cell types. S everal, but not all, of the IL-4 receptor-positive cells showed specif ic IL-13 binding, which was always completely displaced by IL-4. In th e IL-13 receptor-positive cells, the IL-13 either completely or partia lly displaced the labeled IL-4. Further characterization of the IL-13 receptor in two cell Lines, COS-3 and A431, representative of the grou ps of complete and partial displacement of IL-4 by IL-13, respectively , showed that the IL-13 binds with high affinity (K-d approximate to 3 00 pM) to both cells and that the number of binding sites is, in COS-3 cells, equivalent to that for IL-4 and, in A431 cells, is smaller tha n that for IL-4. Cross-linking of labeled IL-13 yielded, on COS-3 cell s, two affinity-labeled complexes of 220 and 70 kDa, and on A431 cells , one complex of 70 kDa; labeled IL-4 yielded on both cells the same p attern of three complexes of 220, 145, and 70 kDa. Altogether, these r esults suggest that the IL-13 receptor may be constituted by a subset of the IL-4 receptor complex associated with at least one additional p rotein.