ePoster Presentation 49th Annual Scientific Meeting of the Australian and New Zealand Society for Immunology 2021

The atypical chemokine receptor ACKR4 scavenges soluble and immobilised CCL21 to regulate peripheral dendritic cell migration (#276)

Cameron R Bastow 1 , Mark D Bunting 2 , Ervin E Kara 1 , Duncan R McKenzie 1 3 , Adriana Caon 1 , Sapna Devi 4 , Lynn Tolley 5 , Scott N Mueller 4 , Ian H Frazer 5 , Natasha Harvey 6 , Mark R Condina 7 , Clifford Young 7 , Peter Hoffman 7 , Shaun R McColl 1 , Iain Comerford 1
  1. Chemokine Biology Laboratory, University of Adelaide, Adelaide, South Australia, Australia
  2. Genome Editing Laboratory, University of Adelaide, Adelaide, SA, Australia
  3. Immunosurveillance Laboratory, The Francis Crick Institute, London, UK
  4. Department of Microbiology and Immunology, University of Melbourne, Melbourne, Victoria, Australia
  5. Diamantina Institute, University of Queensland, Woolloongabba, Queensland, Australia
  6. Centre for Cancer Biology, University of South Australia and SA Pathology, Adelaide, South Australia, Australia
  7. Future Industries Institute, University of South Australia, Mawson Lakes, South Australia, Australia

Directed migration of leukocytes mediated by chemokines underpins a multitude of processes required for the initiation, differentiation and effector phases of adaptive immune responses. In skin, a rising immobilized gradient of lymphatic endothelial cell-derived CCL21 guides CCR7-dependent haptotaxis of mature dendritic cells (DCs) into afferent lymphatic vessels to facilitate priming of immune responses in draining lymph nodes (LNs). The atypical chemokine receptor ACKR4 scavenges CCL21, is broadly expressed in barrier tissues and regulates DC trafficking during the steady-state, cutaneous inflammation and anti-tumour response. However, the mechanism by which ACKR4 regulates peripheral DC migration and the extent to which it regulates the abundance and distribution of CCL21 in peripheral tissues is unknown. Here, we reveal that full-length immobilized CCL21 and a cleaved, solubilized form of CCL21 are present in steady-state barrier tissues, both of which are regulated by ACKR4. In the absence of ACKR4, immobilized CCL21 gradients in the skin are saturated, non-functional, and impair DC homing towards lymphatic vessels and accumulation in LNs. Strikingly, dermal ACKR4 also restricted leaching and accrual of dermal, soluble CCL21 in draining LNs, independent of the ACKR4-scavenging activity previously reported in subcapsular sinus ceiling lymphatic endothelial cells. Dermal CCL21 regulation was dependent on ACKR4 function within radio-resistant cells, where dermal fibroblasts and keratinocytes exhibited the greatest ACKR4 expression. Current studies are focused on characterizing ACKR4 expression by stromal cells utilizing a new ACKR4TdTomato reporter strain in a variety of barrier tissues and organs where ACKR4 regulates CCL21 abundance. Collectively, this work identifies the mechanism through which ACKR4 controls DC migration in barrier tissues and reveals a complex mode of CCL21 regulation in vivo, enhancing our understanding of functional chemokine gradient formation and raising new questions regarding function of solubilized CCL21.