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

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 (