The majority of interleukin cytokines can be divided into molecule families based on structure and function. For example, IL-3 and IL-5 receptors are comprised of a cytokine-specific alpha chain, and a common beta chain. In contrast, IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21 exert their cellular actions following interaction with the common gamma chain of the IL-2 receptor. On the other hand, inclusion in the IL-6 family (IL-6, IL-11, IL-31) is based on a helical cytokine structure, shared receptor subunit makeup and activation of the signal transducing receptor protein glycoprotein 130 (gp130). Equally, cytokines included in the IL-17 family are secreted proteins that share a conserved cysteine-knot structure. R&D Systems also offers products for interleukin molecules which are not currently included within a larger family group (IL-13, IL-16, IL-32, and IL-34).