Binding of IL-1β to IL-1R type II at single cell level

To gain information on the possible biologic role of IL-1R type II (IL-1R_II), expression of the 68-kDa IL-1 binding protein on human lymphoblastoid B cells was investigated at single cell level. Binding of iodinated IL-1β was evaluated by autoradiography on cytosmears of IL-1R_II positive B cell lines RAJI, the RAJI clone 1H7, and STS 25. Results obtained suggest an heterogeneity of IL-1R_II expression within the B cell population, with only 5 to 16% of the cells able to bind IL-1β. Up-regulation of IL-1R_II expression by dexamethasone, evident in conventional binding assays, was achieved through both increase in the number of IL-1 binding cells (14-30%) and augmentation of receptor density on positive cells. By combining autoradiography with immunocytochemical staining, it could be shown that about 80% of IL-1R_II⁺ cells were negative for Ki67, a nuclear antigen expressed from late G₁ to M phase. Cell cycle dependent expression of IL-1R_II was confirmed on cells enriched in different phases of the cell cycle by counterflow centrifugal elutriation. It is thus proposed that IL-1R_II is associated to the cell cycle.