Interleukin 6 is a potent pleiotropic cytokine that regulates cell growth and differentiation and plays an important role in the immune response. IL6Ra is a part of the receptor for interleukin 6 cytokine. IL6Ra binds to IL6 with low affinity, but does not transduce a signal. Signal activation necessitates an association with IL6ST. Activation may lead to the regulation of the immune response, acute-phase reactions and hematopoiesis. Low concentration of a soluble form of IL6 receptor acts as an agonist of IL6 activity. Dysregulated production of IL6 and this receptor are implicated in the pathogenesis of many diseases, such as multiple myeloma, autoimmune diseases and prostate cancer.