The role of the atypical chemokine receptor CCX-CKR in thymocyte development and its influence on the link between innate and adaptive immunity through regulation of dendritic cell migration.

The significance of chemokines in directing cell migration both during homeostasis and immune responses has been appreciated for some time. However, the mechanisms in place to post-translationally regulate cell migration through chemokine modulation are only recently becoming clear. CCX-CKR is a receptor that can scavenge and degrade the ligands of CCR7 and CCR9, two receptors that are crucial during instruction of T cell development in the thymus and dendritic cell migration for initiation of adaptive immune responses. Within the thymus CCL19, CCL21 and CCL25 direct CCR7- and CCR9-expressing thymocytes through distinct thymic compartments, enabling development of a self-MHC restricted and self-tolerant peripheral T cell repertoire. Yet mechanisms outside of transcriptional control that are involved in thymic chemokine regulation have not been well characterised. The aim of this study was to thoroughly investigate the role of CCX-CKR expression on chemokine regulation in the thymus and thymocyte development. Expression of CCX-CKR was detected primarily in cortical thymic epithelial cells, with modest contributions from other thymic stromal populations. Deletion of CCX-CKR led to thymic architecture alterations, reduced levels of CCL19 and CCL25 and a profound decrease in CCL25 (protein) within the cortex. These alterations in chemokine levels and distribution were associated with several defects in the frequency and localisation of thymocyte precursors. Specifically, in CCX-CKR⁻/⁻ thymi, precursor double-negative 2 (DN2) cells accumulated in the medulla and reduced frequencies of DN3 cells were apparent, coincident with reduced numbers of DN3 cells in the cortex. These observations are likely to be the combined outcome of impaired expansion of cortical thymic epithelial cells and reduced outward migration signals in CCX-CKR⁻/⁻ thymi. Additionally, CCXCKR ⁻/⁻ thymi contain increased numbers of CD4⁺CD8⁺ double-positive, CD4⁺ singlepositive and CD8⁺ single-positive cells. Together, these thymic defects were associated with enhanced incidence of inflammatory pathology resembling Sjögren’s syndrome, characterised by lymphocytic infiltrates in salivary glands and liver of 8-10 month old CCX-CKR⁻/⁻ mice. Previous work has implicated CCX-CKR as an important regulator of CCL19 and CCL21 in vivo and deletion of CCX-CKR led to early onset of experimental autoimmune encephalomyelitis (EAE), a T cell mediated autoimmune disease. CCX-CKR was also implicated in promoting effective induction of adaptive immune responses in the LN as evidenced by abrogated T cell proliferation. An important component of both peripheral tolerance induction and initiation of adaptive immune responses is CCR7-dependent migration of antigen-loaded peripheral dendritic cells and naïve T cells to secondary lymphoid organs where antigen presentation to T cells occurs. The contribution of CCXCKR to these processes was investigated in CCX-CKR⁻/⁻ mice. Short-term homing of CD4⁺ T cells to the lymph nodes of CCX-CKR⁻/⁻ mice was impaired yet homeostatic maintenance of T and B cells remained undisturbed. CD207⁺ skin-derived DCs were significantly less abundant in the lymph nodes of CCX-CKR⁻/⁻ mice during both steadystate and inflammation which was associated with reduced numbers of CD207⁺ dermal dendritic cells and increased levels of CCL21 in the skin. Furthermore, during CFAinduced inflammation, both migratory and lymph node-resident dendritic cell numbers were abrogated in the lymph nodes, but not spleen, of CCX-CKR⁻/⁻ mice. Together, these data identify a novel role for CCX-CKR in maintenance of the thymic cortical compartment that is associated with effective thymocyte development. Moreover, CCX-CKR is required to maintain the homeostatic and inflammatory migration of tolerogenic and activating dendritic cells, respectively, to the lymph nodes. Thus, the combination of thymic and skin/LN associated CCX-CKR establishes optimal conditions for central and peripheral tolerance induction leading to the development of self-tolerant adaptive immune responses.

Author dc:creator

• Bunting, Mark Daniel

Advisor dc:contributor.advisor

• McColl, Shaun Reuss

Handle dc:identifier.uri

http://hdl.handle.net/2440/81780

OAI identifier oai:identifier

oai:digital.library.adelaide.edu.au:2440/81780