Abstract
Precursors of dendritic cells (pre-DCs) arise in the bone marrow (BM), egress to the blood, and finally migrate to peripheral tissue, where they differentiate to conventional dendritic cells (cDCs). Upon their activation, antigen-bearing cDCs migrate from peripheral tissue to regional lymph nodes (LNs) in a manner dependent on the chemokine receptor, CCR7. To maintain immune homeostasis, these departing cDCs must be replenished by new cDCs that develop from pre-DCs, but the molecular signals that direct pre-DC trafficking from the BM to the blood and peripheral tissues remain poorly understood. In the present study, we found that pre-DCs express the chemokine receptors CXCR4, CCR2, and CX3CR1, and that each of these receptors has a distinct role in pre-DC trafficking. Flow cytometric analysis of pre-DCs lacking CXCR4 revealed that this receptor is required for the retention of pre-DCs in the BM. Analyses of mice lacking CCR2 or CX3CR1, or both, revealed that they promote pre-DC migration to the lung at steady state. CCR2, but not CX3CR1, was required for pre-DC migration to the inflamed lung. Thus, these multiple chemokine receptors cooperate in a step-wise fashion to coordinate the trafficking of pre-DCs from the BM to the circulation and peripheral tissues.