Expression of interleukin-21, interleukin-21 receptor alpha and related type I cytokines by intravascular graft leukocytes during acute renal allograft rejection

Interleukin-21 (IL-21), a member of the type 1 cytokine family, regulates central functions of immunity. Within this family, signaling is mediated via a receptor complex consisting of a high-affinity receptor chain and the common gamma-chain (IL-2R gamma, CD132). We analyze the mRNA expression of IL-21, IL-21 receptor-alpha (IL-21R alpha) and family members IL-15, IL-2R gamma, IL-21R alpha, IL-15R alpha, IL-2/15R beta, as well as IL-2R alpha (CD25) in leukocytes isolated by vascular perfusion of rat renal allografts. Mononuclear leukocytes expressed increased amounts of IL-21R alpha mRNA and protein during acute rejection. Most IL-21R alpha-positive cells were monocytes. Furthermore, IL-21 and IL-2Ra mRNA expression was strongly increased. No changes in IL-2R gamma, IL-2/15R beta, IL-15, and IL-15R alpha mRNA expression levels were seen. In conclusion, we demonstrate that IL-21Ra expression is induced in intravascular monocytes in vivo in response to allogeneic transplantation. The function of the IL-21/IL-21R system in monocytes and during acute allograft rejection remains to be established. (C) 2008 Elsevier GmbH. All rights reserved.