High- and low-affinity receptors for murine interleukin 6. distinct distribution on b and t cells

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Abstract
The distribution of the murine receptor for interleukin (IL)6 was examined on a variety of cells. Binding sites for IL6 were found on many cell lines including fibroblasts and bone marrow-derived macrophages. The highest density of binding sites was found on B cell hybridomas and plasmacytomas, irrespective of their IL6 dependence for growth. Scatchard analysis carried out with these cells identified about 1000 high-affinity sites (Kd = 25 pM) and 10000 low-affinity sites (Kd = 2.5 nM). The binding was specific for IL6 and led to the internalization of the ligand. Receptors for IL6 were also present on other B cell lines, but binding on normal resting or activated B cells was below the limit of detection (<3 molecules/cell). In contrast, receptors were found on mature thymocytes and on peripheral T cells. However, unlike plasmacytomas and hybridomas, T cells expressed only high-affinity binding sites. The difference in the relative numbers of high- and low-affinity receptors on different cells suggests that IL6 interacts with several proteins, the expression of which varies from one cell type to another.