Seasonal and areal variability in PM2.5 poses differential degranulation and pro-inflammatory effects on RBL-2H3 cells

Abstract

PM2.5 pollution is a widespread environmental and health problem, particularly in China. Besides leading to well-known diseases in the respiratory system, PM2.5 can also alter immune function to induce or aggravate allergic diseases. To determine whether there are temporal and spatial differences in the allergic responses to PM2.5, monthly samples were collected from four regions (urban, industrial, suburban, and rural areas) through a whole year in Nanjing city, China. Inorganic chemical components (metals and water-soluble ions) of PM2.5 were analyzed, and the rat basophil cells (RBL-2H3) exposed to PM2.5 were assessed through quantitative measures of degranulation (β-hex and histamine) and pro-inflammation cytokine (IL-4 and TNF-α) expression. The highest levels of β-hex were measured in winter and spring PM2.5 from urban and industrial areas, or autumn PM2.5 from suburban and rural areas. With respect to histamine, autumn PM2.5 samples were most potent irrespective of the location. Autumn and winter PM2.5 induced higher levels of IL-4 than spring and summer samples. However, spring and autumn PM2.5 caused higher levels of TNF-α. The concentrations of water-soluble ions (NH4+, K+ and Cl−), as well as heavy metals (Pb and Cr), were directly and statistically correlated to the inflammation observed in vitro. In general, the differences between regional and seasonal PM2.5 in stimulating cell degranulation may depend on endotoxin and airborne allergen content of PM2.5. The heavy metals and water-soluble ions in PM2.5 were mostly anthropogenic, which increased the particles' mass-based cellular inflammatory potential, therefore, their health risks, e.g. from vehicular exhaust, coal, and biomass combustion, cannot be ignored.