Mediator protein levels in supernatants of AM and HBEC. GM-CSF, IL-6, MIP-1β, MCP-1, and M-CSF protein levels in supernatants of AM mono-cultures, HBEC mono-cultures and AM/HBEC co-cultures incubated for 24 h with medium alone (control; white bars) or 100 μg/ml of PM10 (black bars). GM-CSF and IL-6 production by AM mono-cultures and AM/HBEC co-cultures stimulated by PM10 increased significantly compared to controls. Exposure to PM10 also increased MIP-1β production by HBEC mono-cultures and AM/HBEC co-cultures and M-CSF production by AM/HBEC co-cultures. The GM-CSF, IL-6 and MIP-1β produced by exposed AM/HBEC co-cultures significantly exceeded the sum of those produced by AM and HBEC mono-cultures exposed separately. Values are means ± SE of five experiments. * p < 0.05 compared with control. † p < 0.05 for exposed AM/HBEC co-cultures compared to the sum of the exposed HBEC and AM mono-cultures.