Efficient Renal Recruitment of Macrophages and T Cells in Mice Lacking the Duffy Antigen/Receptor for Chemokines

The Duffy antigen/receptor for chemokines (DARC) is a chemokine-binding protein that is expressed on erythrocytes and renal endothelial cells. DARC-mediated endothelial transcytosis of chemokines may facilitate the renal recruitment of macrophages and T cells, as has been suggested for neutrophils. We studied the role of Darc in two mouse models of prolonged renal inflammation, one that primarily involves the tubulointerstitium (unilateral ureteral obstruction), and one that requires an adaptive immune response that leads to glomerulonephritis (accelerated nephrotoxic nephritis). Renal expression of Darc and its ligands was increased in both models. Leukocytes effectively infiltrated obstructed kidneys in Darc-deficient mice with pronounced T-cell infiltration at early time points. Development of interstitial fibrosis was comparable in both genotypes. Nephrotoxic nephritis was inducible in Darc-deficient mice, with both an increased humoral immune response and functional impairment during the early phase of disease. Leukocytes efficiently infiltrated kidneys of Darc-deficient mice, with increased cell numbers at early but not late time points. Taken together, renal inflammation developed more rapidly in DARC-deficient mice, without affecting the extent of renal injury at later time points. Thus, genetic elimination of Darc in mice does not prevent the development of renal infiltrates and may even enhance such development during the early phases of interstitial and glomerular diseases in mouse models of prolonged renal inflammation.Chemokines orchestrate the recruitment of inflammatory cells to specific microenvironments in both lymphoid tissue and the sites of inflammation, like the injured kidney.^1,2,3 The Duffy antigen/receptor for chemokines (DARC) is a seven-transmembrane-spanning protein, which binds various inflammatory chemokines of different chemokine subgroups.^1,4,5 It was initially identified as a blood group, the Duffy antigen, involved in rare transfusion reactions. In addition DARC serves as the cellular receptor for invasion of erythrocytes by the malaria parasite Plasmodium vivax.^4,6 DARC is also expressed on endothelium of high endothelial venules in lymphoid tissue and peritubular capillaries in the kidney, where recirculation and extravasation of inflammatory cells takes place.^7,8 The expression of DARC on endothelial cells can be regulated as we demonstrated an increased number of DARC-positive peritubular vessels in biopsies from various forms of human allograft rejection and from glomerulonephritis.^9,10,11 Furthermore, the number of CCR5 positive cells (a receptor for the chemokine CCL5/RANTES) correlated positively with the number of DARC positive vessels, suggesting a potential role of DARC in inflammatory cell recruitment.¹¹However, a functional role for DARC in renal inflammation remains hypothetical, and might depend on the time point and exact inflammatory microenvironment. DARC could function as a chemokine sink on erythrocytes. Darc deficiency might result in an increased inflammatory response, as it has been demonstrated in Darc-deficient mice.^6,12 On the other hand, on endothelial cells DARC is involved in chemokine transcytosis and apical retention, and therefore it might have pro-inflammatory functions.^5,13,14,15 Zarbock et al¹⁶ used two neutrophil-dependent models, ie, ischemia-reperfusion and lipopolysaccharide (LPS)-induced acute renal injury to examine the role of Darc. Darc-deficient mice were protected from renal injury in both models with no renal dysfunction during ischemia-reperfusion injury and only mild renal dysfunction in LPS-induced injury.¹⁶ Neutrophil recruitment to the postischemic kidney was significantly reduced.¹⁶Currently, there is no published evidence for DARC being involved in macrophage or T cell recruitment into diseased kidneys. These cell types are involved in progressive renal diseases. We therefore used two models of renal injury characterized by prominent renal macrophage and T cell accumulation to investigate a potential role of Darc for mediating their renal recruitment. In obstructive nephropathy induced by unilateral ureteral obstruction (UUO) infiltrating macrophages have been identified as mediators of interstitial injury and fibrosis.^17,18 In the nephrotoxic nephritis (NTN) model a T-cell-dependent adaptive immune response leads to immune complex-mediated glomerular and secondary tubulointerstitial injury. This is driven by both macrophages and T cells accumulating in nephritic kidneys.^19,20,21 Here, we show that in both models macrophages and T cells efficiently infiltrate the injured renal tissue in a Darc-independent manner, arguing against a major role for Darc in T cell and monocyte extravasation in these models. Moreover, we demonstrate that renal inflammation developed more rapidly in Darc-deficient mice, without affecting the extent of renal injury at later time points.