The combined effects of endotoxin and dust on the lung.

Endotoxin, a common component of organic dusts in agriculture and in industrial environments such as waste treatment plants, and grain, cotton, and wool mills, has been implicated in the aetiology of respiratory diseases associated with the inhalation of such dusts. The inhalation of endotoxin can reproduce many of the symptoms seen in these diseases. However, some studies have been unable to correlate the endotoxin content of organic dusts with respiratory symptoms, and others have implicated other components of the dusts in the disease processes. Separating the relative contributions of endotoxin and dust to disease has, therefore, been extremely difficult.This project set out to study the interactive effects in the lungs of rats between lipopolysaccharide (LPS), the main active component of endotoxin, and a defined organic particulate (OVA-beads): polystyrene beads conjugated with ovalbumin to render them antigenic. In addition, we studied the effects of LPS on the lung responses to two inorganic dusts, the pathogenic quartz DQ12 and the relatively inert titanium dioxide (TiO.).Intratracheal instillation, of OVA-beads resulted in an inflammatory response, characterised .by increased total cell and neutrophil numbers recovered by bronchoalveolar lavage, which peaked within 24 hours and resolved by day 7 post-instillation. The percentage of lymphocytes recovered in lavage from these animals increased with time, peaking at day 35 post-instillation.The inclusion of 80 ug LPS in the inoculum of OVA-beads produced an enhanced, synergistic neutrophil recruitment, which had also largely resolved by day 7. The LPS co-treatment greatly enhanced the weak serum IgG antibody response to ovalbumin resulting from the lung instillation of OVA-beads.Intratracheal instillation of 0.01, 0.1, or 1 mg quantities of TiO2 or quartz also resulted in an initial dose-dependent inflammatory response which, with the exception of the 0.1 and 1 mg doses of quartz, also resolved within a few days. In animals receiving the two higher doses of quartz there was a slight reduction in cell numbers at day 3, from the initial peak at day 1, but macrophage and neutrophil numbers then increased through day 7 and remained greatly elevated in the 1 mg group and above normal levels in the 0.1 mg group. From earlier studies it is known that this chronic inflammation due to the 1 mg dose persists even at 3 months post-treatment. The inclusion of 10, 40, or 80 ug LPS to the 0.01 mg dust inocula resulted in enhanced, synergistic, but short-lived, inflammatory responses. Thus a strong acute response by the lung to an insult is not by itself sufficient to produce the-chronic inflammation seen with the;! mg-dose of quartz; a minimum amount of quartz is necessary to overload the lung’s clearance mechanisms. These results imply that, in this model, that minimum amount lies between 0.01 and 0.1 mg.Cells recovered by lavage from lungs instilled with the inorganic dusts were cultured overnight :for the. spontaneous production of the pro-inflammatory cytokine TNF. TNF activity peaked at day 3 for PBS and TiO_ groups and was still elevated at day 7 when inflammation had subsided. Cells from LPS or quartz-treated animals gave peak responses on day 7. However, activity was greatly reduced at day 21 in the 0.1 and 1 mg quartz animals, despite continuing inflammation. Co-instillation with LPS and the 0.01 mg doses of TiO_ or quartz reulted in peak TNF activity at day 7 but there was no synergistic effect. Thus the relationship between TNF production in vitro and inflammation in vivo is obviously a complex one.Although the inflammatory-enhancing effects of LPS were short-lived in our model, it is possible that in a working environment where people will be exposed on a regular basis, that the effects might have important, long-term-consequences. The overall conclusion of this study was that co-exposure of workers to endotoxin and dusts, whether organic or inorganic, could result in greater inflammatory reactions within the lung than would result from the dusts alone. Workers inhaling organic dusts containing antigenic material would be at further risk from endotoxin enhancement of potentially damaging immune responses.