Fig. 4.

Nearly-free silanols (NFS) determine the proinflammatory activity of quartz particles in vitro. (A) Release of IL-1β from and (B) cell viability of differentiated THP-1 macrophages 24 h after exposure to vehicle (Ctl) or quartz particles enriched or depleted in NFS, i.e., gQ, gQ-f (10 cm²/mL), mQ-f, mQ-f 800 °C (5 cm²/mL), Min-U-Sil 5 as positive reference quartz (5 cm²/mL), and WC as negative reference particle (5 cm²/mL). Wedges illustrate relative content of NFS. Data are mean ± SEM of three independent experiments. Each dot represents the average of four technical replicates for each independent experiment. For IL-1β values (A), one-way ANOVA with Dunnett’s post hoc test was applied to compare treated groups vs. Ctl; ***P < 0.001. IL-1β values were also compared with a two-tailed Student’s t test: gQ vs. gQ-f: P = 0.007; mQ-f vs. mQ-f 800 °C: P < 0.001. For cell viability (B), one-way ANOVA was n.s.