Swine barn dust stimulates CCL9 expression in mouse monocytes through PKC-delta activation

Exposure to organic barn dusts has been shown to cause numerous lung problems to chronically exposed animal barn workers. Bacterial components in these dusts trigger innate immunity in the lungs that we are still trying to fully characterize. CCL9/MIP-1γ is constitutively expressed in high quantities in the mouse circulation, but at much lower levels in the lungs where it is inducible under certain circumstances. We show here that extracts from hog barn dusts (HDE) are capable of inducing significant increases of CCL9 mRNA and protein in RAW267.4 monocytic cells as well as in mouse lungs. We further show that incubation of CCL9 with HDE results in cleavage of CCL9, which others have shown to increase chemotactic signaling potential. Endotoxin and proteoglycan were determined to be the likely causes of this increase. We additionally present evidence for a role of PKC-delta in this activation. Addition of purified CCL9 protein to HDE treated cell culture resulted in a small, but significant reduction in KC production, suggesting a possible regulatory role for the chemokine.