Flow cytometric analysis of isolated LP CD34⁺ cells from a representative experiment; two-color immunofluorescence staining with FITC-avidin-biotin-MIP-1 complex and PE-conjugated anti-CD34 monoclonal antibody. Control cells were stained with a nonspecific biotinylated protein (soybean trypsin inhibitor) and irrelevant mouse monoclonal conjugated to PE as described in Materials and Methods. Gates for the analysis of MIP-1 receptor expression on CD34⁺ are defined as shown: R1, lymphocyte gate (A); R2, CD34⁺ lymphocytes (B). MIP-1 receptor expression was assessed as mean fluorescence intensity (C) in R2 and percentage of positive cells (D). A negative control using a irrelevant biotinylated protein (shaded histogram) was used to set the quadrant such that at least 99% of the analyzed cells were negative for MIP-1 receptor. Sorting gates are indicated in (D): R3, CD34⁺MIP R⁻; R4, CD34⁺MIP R⁺, and were set to include a strongly negative and positive fraction, respectively.