Effect of DARC Arg89Cys substitution on the binding of anti-Fy antibodies and chemokine to COS-7 cell transfectants.COS-7 cells were transiently transfected by the pcDNA3 expression vector alone (▪) and the recombinant vectors containing the cDNA encoding the Fy^b (Arg⁸⁹) (▨), or Fy^x (Cys⁸⁹) (□) DARC protein. Transfectant cells were analyzed for Duffy antigen expression by flow cytometry with anti-Fy^b PoAb and anti-Fy3 and anti-Fy6 MoAbs and for chemokine binding with ¹²⁵I-IL-8, as described in Materials and Methods. Specific binding of ¹²⁵I-IL-8 yielded 100,000, 45,000, and 2,500 cpm with Fy^b, Fy^x, and mock transfectants, respectively.