CCL17 and CCL22 attenuate CCL5-induced mast cell migration M. Juremalm, N. Olsson and G. Nilsson Research Group on Mast Cell Biology, Department of Genetics and Pathology, The Rudbeck Laboratory, Uppsala University, Uppsala, Sweden Summary Background Mast cells (MCs) accumulate at sites of allergic mucosal inflammation where they act as central effectors and regulatory cells. Chemokines are believed to be crucial for the recruitment of MCs to sites of inflammation. We recently reported that human umbilical cord blood MCs (CBMCs) expresses the CC chemokine receptors, CCR1 and CCR4. We found a unique response profile to ligands of the respective receptors in which, of all tested ligands, only CCL5/RANTES-induced migration. Objective To further investigate the function of CCR4 in MCs. Methods CBMCs were used for competition binding experiments, migration, and intracellular calcium mobilization and release response studies. Results The natural ligands for CCR4, CCL17/TARC and CCL22/MDC could both compete for binding with radiolabelled CCL5. Further, both CCL17 and CCL22 act as CCR4 antagonists by inhibiting CCL5-induced migration. Although both CCL17 and CCL22 caused mobilization of intracellular calcium, none of them induced migration or histamine release. Conclusions These results suggest that CCL5-induced migration of MCs via CCR4 can be regulated by the natural agonists CCL17 and CCL22, which are up-regulated at sites of allergic inflammation. Keywords calcium flux, CCL5, CCL17, CCL22, CCR4, chemotaxis, mast cells Submitted 10 December 2003; revised 17 November 2004; accepted 17 December 2004 Background Mast cells (MCs) are of primary importance in many pathological inflammatory disorders such as allergy, asthma and arthritis [1, 2]. Mature MCs are normally found interspersed in the tissues, but are known to accumulate at sites of both acute and chronic inflammation where they can act as initial effector cells [3]. This relocalization of tissue MCs is believed to be mainly because of chemotactic factors such as chemokines. Until now, five CXC-chemokines, CXCL1, CXCL5, CXCL7, CXCL8 and CXCL12, but only two CC-chemokines, CCL5 and CCL11, have been reported as functional chemokines for human MCs [4–9]. We recently described the expression of two CC-chemokine binding receptors, CCR1 and CCR4, on human cord blood- derived MCs (CBMC) [10]. The migratory response of CBMC towards respective ligands of these receptors exhibited a very restricted and unique pattern. Of the five CCR1 ligands, CCL2, 3, 5, 7 and 14, only CCL5 induced migration. Surprisingly, CCL5 could also induce migration through CCR4, whereas the recognized CCR4 ligands, CCL17 and CCL22, did not. The expression of CCR4 on MCs is particularly interesting since recent reports claim that the CCR4 ligands CCL17 and CCL22 are up-regulated and play dominant roles in T helper 2-type disease conditions such as bronchial asthma [11–13]. The already complex chemokine system has been revealed to be even more intricate with reports of the antagonistic effects of chemokines [14]. In addition to their function as natural agonists, some chemokines have recently been described as natural antagonists, binding to receptors without inducing receptor activation. Subsequently, the binding of natural agonists is inhibited and cellular responses absent. The finding that CCL5 can act as an agonist for CCR4, inducing migration, and the lack of migratory response to CCL17 and CCL22, which are established ligands for CCR4 [15, 16], prompted further investigation of CCR4 expression and function in human MCs. In this study, we demonstrate that CCL17 and CCL22 can compete with CCL5 for binding to CCR4, thereby acting both as CCR4 antagonists for CCL5-induced migration, and as agonists inducing intracellular calcium mobilization but not migration. CCL5, CCL17 and CCL22 seem not to cause degranulation of CBMCs since no histamine release was detected after chemokine treatment. These results imply that CCL17 and CCL22 can fine-tune the migratory response of MCs to CCL5 at sites of allergic inflammation, in which CCL5, CCL17 and CCL22 are produced. Methods Cells Cord blood samples were aspirated into heparinized tubes from the umbilical vein at normal delivery. Fully informed consent was obtained from the mothers of all neonates before Correspondence: Dr Gunnar Nilsson, Department of Genetics and Pathology, Rudbeck Laboratory, Uppsala University, SE-751 85 Uppsala, Sweden. E-mail: Gunnar.Nilsson@genpat.uu.se Clin Exp Allergy 2005; 35:708–712 doi:10.1111/j.1365-2222.2005.02203.x r 2005 Blackwell Publishing Ltd 708