a) CCR1 variants containing different N- and/or C-terminal tags were stably transfected into mammalian cell systems (FlpIn/HEK293, T-Rex/HEK293, FlpIn/T-Rex/HEK293 and pACMV-TetO/HEK293). Where appropriate, cells were induced and cell surface receptor levels detected as described in the experimental procedures. b) Chemokine receptor variants CCR1, CCR2, CCR3 and CCR5 were transfected into HEK293 cells and expression levels of induced and un-induced cells were measured (n=4, shown as mean ± S.D.). Key: CCRXS: CCRX-StrepII, SCCRXH: StrepII-CCRX-His8, HACCRXH: Hemagglutinin-CCRX-His8.