Rat lung inflammatory responses after in vivo and in vitro exposure to various stone particles

Rat lung alveolar macrophages and type 2 cells were exposed for 20 h in vit ro to various stone particles with differing contents of metals and mineral s ( a type of mylonite, gabbro, feldspar, and quartz). The capability to in duce the release of the inflammatory cytokines interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-alpha), and macrophage inflammatory protein-2 ( MIP-2) was investigated. We found marked differences in potency between the various particles, with mylonite being most potent overall, followed by ga bbro, and with feldspar and quartz having an approximately similar order of lower potency. The results also demonstrated differences in cytokine relea se pattern between the two cell types. For all particle types including qua rtz, type 2 cells showed the most marked increase in MIP-2 and IL-6 secreti on, whereas the largest increase in TNF-alpha release was observed in macro phages. To investigate possible correlations between in vitro and in vivo i nflammatory responses, rats were instilled with the same types of particles and bronchoalveolar lavage ( BAL) fluid was collected after 20 h. The resu lts demonstrated a correlation between the in vitro cytokine responses and the number of neutrophilic cells in the BAL fluid. The BAL fluid also showe d a strong MIP-2 response to mylonite. However, this was the only particle type to give a significant cytokine response in the BAL fluid. We further e xamined whether a similar graded inflammatory response would be continued i n type 2 cells and alveolar macrophages isolated from the exposed animals. Again a differential cytokine release pattern was observed between type 2 c ells and macrophages, although the order of potency between particle types was altered. In conclusion, various stone particles caused differential inf lammatory responses after both in vitro and in vivo exposure, with mylonite being the most potent stone particle. The results suggest the alveolar typ e 2 cell to be an important participant in the inflammatory response follow ing exposure to particles.