Cytokines Use Different Intracellular Mechanisms To Upregulate The Membrane Expression Of Cx(3)Cr1 In Human Monocytes

Membrane expression of fractalkine (CX(3)CL1)-receptor (CX(3)CR1) is relevant in monocytes (Mo) because CX(3)CR1-CX(3)CL1 interactions might participate on both, homeostatic and pathologic conditions. We have previously demonstrated that CX(3)CR1 levels are decreased during culture and when Mo are differentiated into dendritic cells, but enhanced when differentiated into macrophages. Regarding soluble factors, lipopolysaccharide (LPS) accelerated the loss of CX(3)CR1, while interleukin (IL)-10 and Interferon-gamma (IFN-gamma) prevented it. However, the comprehensive knowledge about the intracellular pathways that underlay the level of CX(3)CR1 expression in Mo is still incomplete.In the current work, we studied the effect of anti-inflammatory cytokines (IL-4, IL-13, IL-10), alone or together with IFN- gamma on CX(3)CR1 expression. We found that only IL-10 and IFN-gamma separately were able to prevent CX(3)CR1 down-modulation during culture of human Mo. Besides, Mo incubated with IL-10 plus IFN-gamma showed the highest CX(3)CR1 expression by cell, suggesting cooperation between two different mechanism used by both cytokines. By studying intracellular mechanisms triggered by IL-10 and IFN-gamma, we demonstrated that they specifically induced PI3K-dependent serine-phosphorylation of signal transducer and activator of transcription (STAT)3 or STAT1, respectively. Moreover, chemical inhibitors of STAT1 or STAT3 abrogated IFN-gamma or IL-10 effects on CX(3)CR1 expression. Strikingly, only IL-10 increased CX(3)CR1 mRNA level, as consequence of augmenting mRNA stability. CX(3)CR1 mRNA increase was PI3K-dependent, supporting the causal link between the action of IL-10 at the CX(3)CR1 transcript and CX(3)CR1 protein level on Mo. Thus, both cytokines up-regulate CX(3)CR1 expression on human Mo by different intracellular mechanisms.