FIG. 5.

Cell surface exposure of CRs and FPR in LPS-primed and unprimed neutrophils. Neutrophils were preincubated for 30 min in the presence or absence of LPS (10 μg/ml) at 4 or 37°C. Cell surface exposure of CR1 and CR3 as measured by fluorescence-activated cell sorting analysis and cell surface exposure of FPR as measured by binding of radiolabeled fMLF are shown. The data for each cell population, expressed as percentage of the value obtained with control cells (4°C; open bars), are given as mean + SD, n = 6 (CR1 and CR3) or n = 3 (FPR). The control value (100%) for the specific (total minus nonspecific) fMLF binding to FPR was 13.2 fmol/10⁶ cells. Nonspecific binding, measured in the presence of excess unlabeled fMLF, was 10 fmol/10⁶ under all conditions tested. CR1 is a marker for the plasma membrane and secretory vesicles; CR3 and FPR are present in the secretory vesicles as well as in the gelatinase and specific granules.