CCRL2 expression modulates the CXCR2 homodimeric conformation. (A) Membrane expression of CCRL2 in HEK293 T cells transiently cotransfected with empty pcDNA3.1 (lavender) or pcDNA3.1CCRL2+CXCR2-CFP/CXCR2-YFP (red line) at a ratio of ∼5 was determined by flow cytometry (stained with an anti-CCRL2 allophycocyanin [APC] conjugated Ab). CCRL2 expression is shown at a representative ratio of the curve and is maintained at all ratios tested. (B) HEK293 T cells were transiently transfected with pcDNA3.1 or pcDNA3.CCRL2. At 24 hours posttransfection, the cells were cotransfected with a constant amount of CXCR2-CFP and increasing amounts of CXCR2-YFP. A representative experiment is shown. (C) FRET_max and FRET₅₀ values were deduced from data analysis by using a nonlinear regression equation applied to a single binding site model and are representative of 4 independent experiments. Data are expressed as mean ± SEM. FRET₅₀ values from cells co-expressing CXCR2-CFP/CXCR2-YFP + CCRL2 were significantly decreased in the 4 experiments compared with CXCR2-CFP/CXCR2-YFP+pcDNA3.1. *P < .05 by Student t test.