Repetitive organic dust exposure in vitro impairs macrophage differentiation and function

Abstract

Organic dust exposure in the agricultural industry results in significant airway disease and lung function decrease. Mononuclear phagocytes are key cells that mediate the inflammatory and innate immune response after dust exposure. We sought to investigate the effect of organic dust extract (ODE) from modern swine operations on monocyte-derived macrophage (MDM) phenotype and function. Peripheral blood monocytes were obtained by means of elutriation methodology (>99% CD14(+)) and differentiated into macrophages in the presence of GM-CSF (1 week) with and without ODE (0.1%). At 1 week, cells were analyzed by means of flow cytometry for cell-surface marker expression (HLA-DR, CD80, CD86, Toll-like receptor 2, Toll-like receptor 4, mCD14, and CD16), phagocytosis (IgG-opsonized zymosan particles), and intracellular killing of Streptococcus pneumoniae. At 1 week, MDMs were rechallenged with high-dose ODE (1%), LPS, and peptidoglycan (PGN), and cytokine levels (TNF-alpha, IL-6, IL-10, and CXCL8/IL-8) were measured. Comparisons were made to MDMs conditioned with heat-inactivated dust, endotoxin-depleted dust, LPS, and PGN to elucidate ODE-associated factors. Expression of HLA-DR, CD80, and CD86; phagocytosis; and intracellular bacterial killing were significantly decreased with ODE-challenged versus control MDMs. Responses were retained after marked depletion of endotoxin. PGN, LPS, and PGN plus LPS significantly reduced MDM surface marker expression and, except for LPS alone, also reduced phagocytosis. ODE-challenged MDMs had significantly diminished cytokine responses (TNF-alpha, IL-6, and IL-10) after repeat challenge with high-dose ODE. Cross-tolerant cytokine responses were also observed. Repetitive organic dust exposure significantly decreases markers of antigen presentation and host defense function in MDMs. Bacterial cell components appear to be driving these impaired responses.