A novel methodology for defining stromal expression of atypical chemokine receptors in vivo

Analysis of chemokine receptor, and atypical chemokine receptor, expression is frequently hampered by the lack of availability of high-quality antibodies and the species-specificity of those that are available. We have previously described methodology utilising Alexa-Fluor labelled chemokine ligands as versatile reagents to detect receptor expression. Previously this has been limited to haematopoietic cells and methodology for assessing expression of receptors on stromal cells has been lacking. Amongst chemokine receptors the ones most frequently expressed on stromal cells belong to the atypical chemokine receptor subfamily. These receptors do not signal in the classic sense in response to ligand but scavenge their ligands and degrade them and thus sculpt in vivo chemokine gradients. Here we demonstrate the ability to use either intratracheal, or intravenous, Alexa-Fluor labelled chemokine administration to detect stromal cell populations expressing the atypical chemokine receptor ACKR2. Using this methodology we demonstrate, for the first time, expression of ACKR2 on blood endothelial cells. This observation sets the lung aside from other tissues in which ACKR2 is exclusively expressed on lymphatic endothelial cells. In summary therefore we described a novel method for the in situ labelling of atypical chemokine receptor expressing cells appropriate for subsequent flow cytometric analysis. We propose that this methodology will work in a range of species and for a range of receptors and therefore will have significant versatility