Cutting Edge: Scavenging of Inflammatory CC Chemokines by the Promiscuous Putatively Silent Chemokine Receptor D6

Abstract

In an effort to define the actual function of the promiscuous putatively silent chemokine receptor D6, transfectants were generated in different cell types. Engagement of D6 by inflammatory CC chemokines elicited no calcium response nor chemotaxis, but resulted in efficient agonist internalization and degradation. Also in lymphatic endothelium, where this receptor is expressed in vivo, D6 did not elicit cellular responses other than ligand internalization and degradation. In particular, no evidence was obtained for D6-mediated transcytosis of chemokines in the apical-to-basal or basal-to-apical directions. These results indicate that D6 acts as an inflammatory chemokine scavenging nonactivatory decoy receptors and suggest that in lymphatic vessels D6 may function as a gatekeeper for inflammatory CC chemokines, by clearing them and preventing excessive diffusion via afferent lymphatics to lymph nodes.

Increased inflammation in mice deficient for the chemokine decoy receptor D6

“…Previous studies reporting lack of signaling and decoy activity of D6 were focused on the human molecule [9,16]. It was therefore important to assess whether mouse D6 shares these key properties with its human orthologue.…”

“…3C). Since D6 is expressed on lymphatic endothelium in the skin [12], and it was suggested to act as a gatekeeper for inflammatory chemokine transfer to LN [7,16], it was important to investigate the LN reaction to CFA injection. In resting conditions, D6 -/-mice had normal LN histology (data not shown) and cellularity (4.07AE0.17 and 3.92AE0.19 Â 10 6 cells per LN in WT and D6 -/-mice, respectively).…”

“…Subsequently, decoy receptors have been identified in the IL-1, TNF, IL-10, IL-4/IL-13 and other receptor families [7,20]. On the basis of structural analysis [7] and in vitro data [16], D6 was suggested to act as a decoy and scavenger for inflammatory CC chemokines [16]. The results reported here, by demonstrating that the absence of D6 results in an anticipated and exacerbated local inflammation and enhanced LN reactivity, are entirely consistent with this hypothesis, and demonstrate that D6 is a unique 7-transmembranedomain decoy receptor, ideally adapted for chemokine scavenging and strategically located to tune inflammation in tissues and draining LN.…”

“…Chemokine scavenging was analyzed as previously described [13,16]. Briefly, cells (2Â10 5 ) were incubated at 37 C in 200 ll of binding buffer (RPMI-1640, 4 mM HEPES pH 7.4, 1% BSA) supplemented with 10 ng/ml of the indicated chemokines.…”

“…Differently from other chemokine receptors [11], D6 expression is restricted to non-hematopoietic cells such as endothelial cells lining afferent lymphatics of skin [12], and placenta [9]. D6 binds most inflammatory, but not homeostatic, CC chemokines [9,13], internalizes constitutively [14,15] and targets the ligand for degradation [16].…”