As discussed in the following paragraph, LXR activation following the phagocytosis of apoptotic
cells could be involved in the generation and maintenance of tumor-specific T-cell tolerance (Fig. 1A) [20, 21]. LXR signaling has also been shown to maintain homeostatic levels of neutrophils. Indeed, aged neutrophils are cleared from the circulation Enzalutamide price by resident APCs through the transduction of “eat-me” signals that upregulate LXR-dependent transcription of Mertk and its partner Gas6 . Altogether, these results suggest that LXRα, LXRβ, or both isoforms control various biologic functions of mouse macrophages and DCs depending on the pathophysiologic context. For instance, the exposure of macrophages and DCs to oxysterols Sotrastaurin chemical structure concomitantly to the engagement of TLRs or the exposure to cytokines/growth factors seems to mainly induce an LXRα-mediated activity,
whereas in steady-state conditions, LXRα/β-mediated activity would take place [10, 17, 19]. LXRα has been implicated in the regulation of some functions of human monocyte-derived DCs. During the differentiation of human DCs from circulating monocytes there is a marked upregulation of LXRα transcripts, whereas LXRβ expression is maintained at very low levels . LXRα activation during the differentiation of monocyte-derived DCs blocks the expression of the actin-bundling protein fascin, thereby interfering with immune synapse formation .
This ultimately diminishes the T-cell stimulatory ability of maturing monocyte-derived DCs with activated LXRs. Similarly, LXRα activation during DC maturation inhibits the expression of the chemokine receptor CCR7 and, therefore, impairs Fluorometholone Acetate DC migration toward the chemokine CCL19 [10, 24, 25]. LXRα silencing in DCs partly abrogates CCR7 downregulation by oxysterols, indicating that in conditions where DCs are activated by inflammatory or bacterial-derived stimuli (i.e., LPS), oxysterols seem to mainly engage and activate DCs via the LXRα isoform. This has also been confirmed by a recent report demonstrating that Prostaglandin E2, which has been shown to license monocyte-derived DCs to express functional CCR7 receptors , downregulates LXRα but not LXRβ expression in monocyte-derived DCs as well as in ex vivo purified DCs, thus enhancing CCR7 expression and DC migration toward CCL21  and highlighting the context-dependent outcomes of LXRα and LXRβ activation. Interestingly, Feig et al. have recently shown that in a different stage of DC differentiation (i.e., immature DCs), LXR ligands induce CCR7 expression, a function dependent on the activation of both LXRα and -β isoforms . Therefore, oxysterols exert opposite effects on the expression of CCR7 depending on the stage of DC differentiation (immature versus maturing DCs), possibly through the differential activation of LXRα and/or LXRβ isoforms.