LUNG EPITHELIAL-CELL (A549) INTERACTION WITH UNOPSONIZED ENVIRONMENTAL PARTICULATES - QUANTITATION OF PARTICLE-SPECIFIC BINDING AND IL-8 PRODUCTION

The A549 cell line was used to model in vitro the interaction of alveo lar epithelium with environmental particulates. Confocal and electron microscopy demonstrated A549 binding and internalization of titanium d ioxide (TiO2), iron oxide (Fe2O3), concentrated ambient air particulat es (CAPs), and the fibrogenic particle alpha-quartz. Flow cytometry al lowed quantitation of particle binding by measuring increased right an gle light scatter (RAS) (TiO2 [40 mu g/mL], Fe2O3 [100 mu g/mL], alpha -quartz [200 mu/mL], or CAPs [40 mu g/mL] fold increase RAS:8.1+/-0.9, 4.3+/-0.4, 2+/-0.1, 1.6+/-0.1, respectively). With this quantitative assay, binding of particles was found to be calcium-dependent for TiO2 and Fe2O3 (% inhibition, 61.0+/-1.9, 40.0+/-5.6, respectively), while alpha-quartz binding was calcium-independent. A panel of polyanionic ligands known to inhibit scavenger-type receptors was used to identify binding mechanisms for environmental particulates. Both heparin and p olyinosinic acid (polyl), but not the control polyanion chondroitin su lfate, caused marked inhibition of particulate binding by A549 cells ( e.g., TiO2 [40 mu g/mL] binding; polyl, heparin, and chondroitin sulfa te: 73.8+/-3.5, 75.5+/-6.0, 7.5+/-6.7% inhibition, respectively; mean/-SE, n greater than or equal to 4), indicating that scavenger recepto r(s), albeit those distinct from the heparin-insensitive acetylated-LD L receptor, mediate particulate binding. The particulates ability to s timulate interleukin (IL-8) production in A549 cells was also tested. alpha-quartz, but not TiO2 or CAPs, caused a dose-dependent production of IL-8 (range 1-6 ng/mL), demonstrating a particle-specific spectrum of epithelial cell cytokine (IL-8) response. The results suggest that lung epithelial cell interaction with environmental particles is medi ated by distinct receptors and can lead to particle-dependent cytokine responses.