HETEROGENEITY OF TYPE-II INTERLEUKIN-1 RECEPTORS - HETEROGENEITY OF B-CELL INTERLEUKIN-1 BINDING CREATED BY DIMERIZATION OF TYPE-II INTERLEUKIN-1 RECEPTORS

The binding of IL-1alpha and IL-1beta to two human lymphoblastoid B-cell lines, Raji and RPMI 1788, was compared with binding to the murine T-cell line, EL4. Dramatic differences in IL-1 binding were observed. Both human B-cell lines bound much less IL-1alpha than IL-1beta, expressed 5-10 times more receptors per cell for IL-1beta than did the EL4 cell line, and demonstrated a large difference in the ability of IL-1alpha to compete with IL-1beta for binding. The B-cell lines demonstrated a low number of high-affinity IL-1alpha receptors and a large number of IL-1alpha receptors with a much lower affinity. Inhibition studies demonstrated that only IL-1beta could compete for the binding of radiolabeled IL-1beta to the B-cell IL-1R. Furthermore, SDS-PAGE analyses of lysates of the B-cell lines that had been affinity cross-linked with I-125-IL-1alpha revealed two bands corresponding to IL-IR structures of 60 and 110 kD. These results coupled with a nonequilibrium binding study suggested a dimerization of a common type-II IL-IR polypeptide, the dimer being responsible for the high-affinity IL-1alpha-binding site of the B-cell lines.