Inhibition of JAKs in macrophages increases lipopolysaccharide-induced cytokine production by blocking IL-10-mediated feedback.

Macrophages are an important source of cytokines following infection. Stimulation of macrophages with TLR agonists results in the secretion of TNF-α, IL-6, and IL-12, and the production of these cytokines is controlled by multiple feedback pathways. Macrophages also produce IL-10, which acts to inhibit proinflammatory cytokine production by macrophages via a JAK/STAT3-dependent pathway. We show in this paper that, Ruxolitinib, a recently described selective inhibitor of JAKs, increases TNF, IL-6, and IL-12 secretion in mouse bone marrow-derived macrophages stimulated with LPS. This effect is largely due to its ability to block IL-10-mediated feedback inhibition on cytokine transcription in macrophages. Similar results were also obtained with a second structurally unrelated Jak inhibitor, Tofacitinib. In addition, LPS induced the production of IFN-β, which was then able to activate JAKs in macrophages, resulting in the stimulation of STAT1 phosphorylation. The initial induction of IL-10 was independent of JAK signaling; however, inhibition of JAKs did reduce IL-10 secretion at later time points. This reflected a requirement for the IFN-β feedback loop to sustain IL-10 transcription following LPS stimulation. In addition to IL-10, IFN-β also helped sustain IL-6 and IL-12 transcription. Overall, these results suggest that inhibition of JAKs may increase the inflammatory potential of macrophages stimulated with TLR4 agonists.