TNFα and IL-6 Responses to Particulate Matter in Vitro: Variation According to PM Size, Season, and Polycyclic Aromatic Hydrocarbon and Soil Content

BACKGROUND: Observed seasonal differences in particulate matter (PM) associations with human health may be due to their composition and to toxicity-related seasonal interactions. OBJECTIVES: We assessed seasonality in PM composition and in vitro PM pro-inflammatory potential using multiple PM samples. METHODS: We collected 90 weekly PM10 and PM2.5 samples during the rainy-warm and dry-cold seasons in five urban areas with different pollution sources. The elements, polycyclic aromatic hydrocarbons (PAHs), and endotoxins identified in the samples were subjected to principal component analysis (PCA). We tested the potential of the PM to induce tumor necrosis factor alpha (TNF alpha) and interleukin 6 (IL-6) secretion in cultured human monocytes (THP-1), and we modeled pro-inflammatory responses using the component scores. RESULTS: PM composition varied by size and by season. PCA identified two main components that varied by season. Combustion-related constituents (e.g., vanadium, benzo[a] pyrene, benzo[a] anthracene) mainly comprised component 1 (C-1). Soil-related constituents (e.g., endotoxins, silicon, aluminum) mainly comprised component 2 (C-2). PM from the rainy-warm season was high in C-2. PM (particularly PM2.5) from the dry-cold season was rich in C-1. Elevated levels of cytokine production were associated with PM10 and C-2 (rainy-warm season), whereas reduced levels of cytokine production were associated with PM2.5 and C1 (dry-cold season). TNFa secretion was increased following exposure to PM with high (vs. low) C-2 content, but TNFa secretion in response to PM was decreased following exposure to samples containing >= 0.1% of C-1-related PAHs, regardless of C-2 content. The results of the IL-6 assays suggested more complex interactions between PM components and particle size. CONCLUSIONS: Variations in PM soil and PAH content underlie seasonal and PM size-related patterns in TNFa secretion. These results suggest that the mixture of components in PM explains some seasonal differences in associations between health outcomes and PM in epidemiologic studies.