Characterization of oak and birch dust-induced expression of cytokines and chemokines in mouse macrophage RAW 264.7 cells

Occupational exposure to wood dust is related to several respiratory diseases, such as allergic rhinitis, chronic bronchitis, and asthma. However, virtually nothing is known about molecular mechanisms behind wood dust-induced pulmonary inflammation. To elucidate the effects of wood dust exposure on cytokine and chemokine expression in murine macrophage cell line cells, mouse RAW 264.7 cells were exposed to two selected hardwood dusts, oak and birch. TiO2 and LPS were used as controls. Expression patterns of several cytokines, chemokines, and chemokine receptors were assessed by real-time quantitative PCR system and by ELISA. Exposure to birch dust caused a major increase in TNF-alpha and IL-6 protein levels whereas a weaker induction of TNF-alpha protein was found after exposure to oak dust. Inorganic TiO2 dust did not induce significant cytokine expression. With respect to the chemokines, a dose-dependent, about 10-fold induction of CCL2 mRNA and protein was found after exposure to birch dust. Oak dust induced weakly CCL2 protein. Similarly, birch dust induced a strong expression of CCL3, CCL4, and CXCL2/3 mRNA whereas only moderate levels of these chemokine mRNAs were detected after oak dust exposure. In contrast, expression of CCL24 mRNA was inhibited by more than 40-fold by both oak and birch dusts. TiO2 dust induced about five-fold expression of CCL3 and CCL4 mRNA but did not affect significantly other chemokines. These results suggest that exposure to birch or oak dusts may influence the development of the inflammatory process in the airways by modulating the expression of macrophage-derived cytokines and chemokines.