Comparative airway inflammatory response of normal volunteers to ozone and lipopolysaccharide challenge

Abstract

Ozone and lipopolysaccharide (LPS) are environmental pollutants with adverse health effects noted in both healthy and asthmatic individuals. The authors and others have shown that inhalation of ozone and LPS both induce airway neutrophilia. Based on these similarities, the authors tested the hypothesis that common biological factors determine response to these two different agents. Fifteen healthy, nonasthmatic volunteers underwent a 0.4 part per million ozone exposure for 2 h while performing intermittent moderate exercise. These same subjects underwent an inhaled LPS challenge with 20,000 LPS units of Clinical Center Reference LPS, with a minimum of 1 month separating these two challenge sessions. Induced sputum was obtained 24 h before and 4-6 h after each exposure session. Sputum was assessed for total and differential cell counts and expression of cell surface proteins as measured by flow cytometry. Sputum supernatants were assayed for cytokine concentration. Both ozone and LPS challenge augmented sputum neutrophils and subjects' responses were significantly correlated (R = .73) with each other. Ozone had greater overall influence on cell surface proteins by modifying both monocytes (CD14, human leukocyte antigen [HLA]-DR, CD11b) and macrophages (CD11b, HLA-DR) versus LPS where CD14 and HLA-DR were modified only on monocytes. However, LPS significantly increased interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha, with no significant increases seen after ozone challenge. Ozone and LPS exposure in healthy volunteers induce similar neutrophil responses in the airways; however, downstream activation of innate immune responses differ, suggesting that oxidant versus bacterial air pollutants may be mediated by different mechanisms.

Figure 1

Neutrophil responses comparing O₃ and CCRE challenge. Baseline values are labeled as pre-O₃ and pre-LPS. O₃ and CCRE exposure both increased % neutrophils in induced sputum (A), whereas only ozone significantly increased neutrophils per milligram of sputum (B). (See colour version of this figure online at www.informahealthcare.com/ipi)

Figure 2

Cytokines from sputum supernatants comparing O₃ and CCRE challenge. Baseline values are labeled as pre- O₃ and pre-LPS. Only CCRE challenge significantly increased the concentration of IL-1β (A), IL-6 (B), and TNF-α (D). Neither O₃ nor CCRE challenge changed levels of IL-8 (C). (See colour version of this figure online at www.informahealthcare.com/ipi)

Figure 3

Cell surface markers of sputum monocytes comparing O₃ and CCRE challenge. Baseline values are labeled as pre-O₃ and pre-LPS. CD11b (A) was up-regulated by O₃ alone. CD14 (B) and HLA-DR (D) were up-regulated by O₃ and CCRE. Neither challenge modality up-regulated CD86 (C). CD11b n = 12 for O₃ and n = 12 for CCRE; CD14 n = 14 for O₃ and n = 12 for CCRE; CD86 n = 13 for O₃ and n = 11 for CCRE; and HLA-DR n = 13 for O₃ and n = 12 for CCRE. (See colour version of this figure online at www.informahealthcare.com/ipi)

Figure 4

Cell surface markers of sputum macrophages comparing O₃ and CCRE challenge. Baseline values are labeled as pre-O₃ and pre-LPS. CD11b (A) and HLA-DR (D) were up-regulated by O₃ alone, whereas CD14 (B) and CD86 (C) were not affected by O₃ or CCRE challenge. CD11b n = 11 for O₃ and n = 12 for CCRE; CD14 n = 12 for O₃ and n = 12 for CCRE; CD86 n = 11 for O₃ and n = 11 for CCRE; and HLA-DR n = 12 for O₃ and n = 12 for CCRE.(See colour version of this figure online at www.informahealthcare.com/ipi)

Figure 5

Correlation analysis comparing fold change from baseline % neutrophils in induced sputum. x-axis denotes O₃ challenge and y-axis denotes CCRE (LPS) challenge. N = 12 pairs to generate the linear regression line. A positive correlation was noted between ozone- and LPS-induced sputum neutrophilia (r = .73, p = .007). With inclusion of the outlier denoted by the open circle, r = .59, p = .03.