Pulmonary chemokine expression is coordinately regulated by STAT1, STAT6, and IFN-γ

The expression of distinct chemokines within the asthmatic lung suggests that specific regulatory mechanisms may mediate various stages of asthmatic disease. Global transcript expression profiling was used to define the spectrum and kinetics of chemokine involvement in an experimental murine model of asthma. Seventeen chemokines were induced in the lungs of allergen-inoculated mice, as compared with saline-treated mice. Two (CXCL13 and CCL9) of the 17 identified chemokines have not previously been associated with allergic airway disease. Seven (7 of 17; CCL2, CCL7, CCL9, CCL11, CXCL1, CXCL5, CXCL10) of the allergen-induced chemokines were induced early after allergen challenge and remained induced throughout the experimental period. Three chemokines (CXCL2, CCL3, and CCL17) were induced only during the early phase of the inflammatory response after the initial allergen challenge, while seven chemokines (CCL6, CCL8, CCL12, CCL22, CXCL9, CXCL12, and CXCL13) were increased only after a second allergen exposure. Unexpectedly, expression of only three chemokines, CCL11, CCL17, and CCL22, was STAT6 dependent, and many of the identified chemokines were overexpressed in STAT6-deficient mice, providing an explanation for the enhanced neutrophilic inflammation seen in these mice. Notably, IFN-γ and STAT1 were shown to contribute to the induction of two STAT6-independent chemokines, CXCL9 and CXCL10. Taken together, these results show that only a select panel of chemokines (those targeting Th2 cells and eosinophils) is positively regulated by STAT6; instead, many of the allergen-induced chemokines are negatively regulated by STAT6. Collectively, we demonstrate that allergen-induced inflammation involves coordinate regulation by STAT1, STAT6, and IFN-γ.