Expression of CXC-chemokine receptors on PMN after pretreatment with NAP-2 or IL-8. Neutrophils were pretreated with various concentrations of NAP-2 (A) or IL-8 (B) or left unexposed for 10 minutes. Subsequently the surface expression of CXCR-1 (•) and CXCR-2 (○) was determined by means of two specific antibodies against each receptor type (MoAb RII115 and MoAb SE-2, respectively) and recorded by flow cytometry as median fluorescence intensity after staining with fluorescein-conjugated goat α-mouse IgG. Unspecific fluorescence of PMN as determined in the absence of receptor-specific antibodies was subtracted (the proportion of unspecific binding was as depicted in Fig 2). Data were calculated as the percentage of the controls that received no chemokine pretreatment and represent mean ± SD of four independent experiments.