A biochemical and kinetic analysis of the interleukin-1 receptor. Evidence for differences in molecular properties of IL-1 receptors.

This study describes the biochemical characterization and kinetic analysis of the interleukin-1 (IL-1) receptor in Raji human B-lymphoma and EL4 murine T-lymphoma cells. The internalization of 125I-IL-1 was studied in both cell types by an acid extraction technique which removes surface bound ligand. At 37 degrees C, binding to Raji IL-1 receptors was almost entirely cell surface (91%). EL4 cells, in contrast, internalized 59% of ligand at this temperature and this was almost totally inhibited by sodium azide. Receptor binding studies showed that the B-cells had a lower binding affinity but much higher receptor density per cell (KD = 2.1 nM, Ro = 7709) than the T-cells (KD = 0.4 nM, Ro = 241). The receptor binding affinity of two IL-1 analogs, Glu-4 and clone 18, was determined in competitive binding studies. In the B-cells the analogs had binding affinities of 25 and 90%, respectively, whereas in the T-cells the affinities were 0.2 and 200%, respectively. Chemical cross-linking studies showed that the IL-1 receptor in B-cells had a lower molecular weight than that in T-cells (68 kDa compared to 80 kDa). In summary these studies demonstrate that structural differences exist between IL-1 receptors in Raji and EL4 cells.