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* Department of Microbiology, Immunology and Molecular Genetics, and
Graduate Center for Toxicology, University of Kentucky Medical Center, Lexington, KY 40536
Despite an immunosuppressive lung environment, alveolar macrophages (AM) retain the capacity to respond to microorganisms. This report demonstrates that IL-10, constitutively produced by normal alveolar epithelium, stimulates signal transduction through the IL-10R on AM and that IL-10R function can be inhibited by stimulation of Toll-like receptor (TLR) on AM. IL-10 mRNA and protein were constitutively expressed in normal alveolar epithelium of mice, and IL-10R were constitutively expressed on normal murine AM. Stimulation of AM through TLR2, TLR4, or TLR9 was sufficient to inhibit IL-10R signal transduction, including phosphorylation and nuclear translocation of STAT3 transcription factor. Inhibition of IL-10R function by TLRs was not associated with a decrease in IL-10R expression, but did require expression of the myeloid differentiation factor 88 adaptor protein. Continuous exposure of macrophages to IL-10 caused sustained expression of the chemokine receptors CCR1 and CCR5. However, the addition of TLR ligands inhibited IL-10-induced expression of CCR1 and CCR5. Finally, exposure of macrophages to TLR ligands blocked the ability of IL-10 to inhibit the induction of TNF-
by C2-ceramide. These findings demonstrate a novel regulatory mechanism that may allow AM to overcome inhibitory effects of constitutive IL-10 in the lungs that may permit a more effective response to pulmonary infections.
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