mAbs against human IL-8 receptor A (IL-8R-A) were generated by immunizing mice with either: 1) peptides corresponding to various extracellular domains of IL-8R-A or 2) transfected 293 cells expressing IL-8R-A (293-71 cells). Among the seven peptides used for immunization, only the peptide corresponding to residues 2-19 of IL-8R-A produced Abs capable of recognizing native IL-8R-A on 293-71 cells. We screened for hybridomas secreting mAbs capable of binding strongly to peptide 2-19 in an ELISA and capable of recognizing native IL-8R-A in flow cytometry experiments with 293-71 cells. Two clones secreting mAbs capable of recognizing native IL-8R-A were selected for further characterization. None of these mAbs were able to block the binding of 125I-IL-8 to 293-71 cells. We also screened hybridomas derived from mice immunized with the intact receptor expressed on transfected 293-71 cells and identified several clones secreting mAbs capable of recognizing native IL-8R-A in flow cytometry experiments. Two of these mAbs were capable of blocking the binding of 125I-IL-8 to 293-71 cells. The epitopes, recognized by these blocking mAbs and by the other nonblocking mAbs derived from the peptide immunization, mapped to the NH2-terminal region of IL-8R-A using an ELISA against synthetic peptides: the two blocking mAbs mapped to residues 2-14 of IL-8R-A, whereas the nonblocking mAbs mapped to residues 2-11. Furthermore, flow cytometry analysis of IL-8 receptor mutants showed that Asp6 plays an important role in the binding of the blocking mAbs but not in the binding of the nonblocking mAbs. Conversely, a mutation of Asp11 to Lys disrupts the binding of one of the nonblocking mAbs (4C8) but has no effect on recognition by others. Analysis of the affinity of these mAbs for IL-8R-A demonstrated that blocking mAbs have affinities at least sevenfold higher than the nonblocking mAbs.