Differential binding of IL‐ 1α and IL‐ 1β to receptors on B and T cells

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Abstract
The interleukin 1 receptors (IL‐1R) on the human B lymphoma RAJI and on the murine thymoma EL4‐6.1 have been characterized. Equilibrium binding analysis using both 125I‐labeled IL‐1α and IL‐1β showed that RAJI cells have a higher number of binding sites/cell for IL‐1β (2400, K d 2.2 nM) than for IL‐1α (316, K d 0.13 nM). On the other hand, EL4‐6.1 cells have more receptors/cell for IL‐1α (22 656, K d 1 nM) than for IL‐1β (2988, K d 0.36 nM). Dexamethasone (DXM) induced on RAJI cells a time‐dependent increase in binding sites for both IL‐1β and IL‐1α without affecting their binding affinities. However, while receptor‐bound 125I‐IL‐1α was displaced with equal efficiency by both IL‐1 forms, only unlabeled IL‐1β could effectively displace 125I‐IL‐1β. Cross‐linking experiments indicated that RAJI cells have a predominant IL‐1R of about 68 kDa, while EL4‐6.1 cells have an IL‐1‐binding polypeptide of 80 kDa. These results suggest that B and T cells possess structurally different IL‐1R with distinct binding properties for IL‐1α and IL‐1β.