IL-4 Pretreatment Selectively Enhances Cytokine and Chemokine Production in Lipopolysaccharide-Stimulated Mouse Peritoneal Macrophages

Abstract Although well recognized for its anti-inflammatory effect on gene expression in stimulated monocytes and macrophages, IL-4 is a pleiotropic cytokine that has also been shown to enhance TNF-α and IL-12 production in response to stimulation with LPS. In the present study we expand these prior studies in three areas. First, the potentiating effect of IL-4 pretreatment is both stimulus and gene selective. Pretreatment of mouse macrophages with IL-4 for a minimum of 6 h produces a 2- to 4-fold enhancement of LPS-induced expression of several cytokines and chemokines, including TNF-α, IL-1α, macrophage-inflammatory protein-2, and KC, but inhibits the production of IL-12p40. In addition, the production of TNF-α by macrophages stimulated with IFN-γ and IL-2 is inhibited by IL-4 pretreatment, while responses to both LPS and dsRNA are enhanced. Second, the ability of IL-4 to potentiate LPS-stimulated cytokine production appears to require new IL-4-stimulated gene expression, because it is time dependent, requires the activation of STAT6, and is blocked by the reversible protein synthesis inhibitor cycloheximide during the IL-4 pretreatment period. Finally, IL-4-mediated potentiation of TNF-α production involves specific enhancement of mRNA translation. Although TNF-α protein is increased in IL-4-pretreated cells, the level of mRNA remains unchanged. Furthermore, LPS-stimulated TNF-α mRNA is selectively enriched in actively translating large polyribosomes in IL-4-pretreated cells compared with cells stimulated with LPS alone.