Mechanisms involved in pro-inflammatory responses to traffic-derived particulate matter (PM) in THP-1 macrophages compared to HBEC3-KT bronchial epithelial cells

The pro-inflammatory responses in THP-1-derived macrophages and human bronchial epithelial cells (HBEC3-KT) were examined after exposure to size-fractioned particulate matter (PM) sampled in two road tunnels. All tunnel PM samples induced release and expression of CXCL8 and IL-1β in THP-1 macrophages (50 µg/mL) and HBEC3-KT cells (100 µg/mL), but the potency of the samples differed between the cell types. The road tunnel PM induced pro-inflammatory responses in the macrophages to a much higher extent than diesel exhaust particles (DEP) and particles derived from the stone materials used in the asphalt. Tunnel PM induced a markedly higher increase in cytochrome P450 (CYP)1A1 expression in HBEC3-KT cells than in THP-1 macrophages. The content of organic carbon (OC) in PM correlated to the release of CXCL8 in HBEC3-KT cells, but not in THP-1 macrophages. Moreover, the aryl hydrocarbon receptor (AhR)-inhibitor CH223191 and the antioxidant N-acetyl cysteine (NAC) reduced the PM-induced cytokine release in the macrophages to a lower extent than in HBEC3-KT. In contrast, a toll-like receptor (TLR)2 antibody markedly reduced the PM-induced responses in THP-1 macrophages, but not in HBEC3-KT. A TLR4 antibody was without effect in both cell types. The levels of the microbial TLR2-ligand β-glucan in the PM samples were in a range that might be sufficient to induce pro-inflammatory responses. However, a microbial-independent mechanism could also be involved. In support of such a mechanism, the pro-inflammatory responses to a sample of α-quartz (Min-U-Sil 5), with low levels of β-glucan, were reduced by anti-TLR2. In conclusion, our results indicate that traffic-derived PM exert pro-inflammatory responses in THP-1 macrophages and HBEC3-KT cells via different PM constituents and mechanisms. OC/AhR-dependent mechanisms appeared to be important for PM-induced CXCL8 responses in HBEC3-KT cells, while the cytokine responses in THP-1 macrophages seemed to involve TLR2-mediated activation, either via β-glucan-dependent or -independent mechanisms.