Daniele D'Ambrosio

Beta2-agonists prevent Th1 development by selective inhibition of interleukin 12.

Interleukin 12 (IL-12) plays a central role in the immune system by skewing the immune response towards T helper 1 (Th1) type responses which are characterized by high interferon-gamma and low IL-4 production. In this report we present evidence that beta2-agonists inhibit IL-12 production by both human monocytes in response to lipopolysaccharide (LPS) and dendritic cells stimulated via CD40. Inhibition of IL-12 production is selective, as other cytokines produced by monocytes are unaffected. IL-12 inhibition is dependent on beta2-adrenoceptor stimulation and correlates with increased levels of intracellular cAMP. In conjunction with their ability to suppress IL-12 production, when beta2-agonists are added at priming of neonatal T lymphocytes, they inhibit the development of Th1-type cells, while promoting T helper 2 (Th2) cell differentiation. Further, the in vivo administration of a therapeutic dose of salbutamol results in the selective inhibition of IL-12 production by whole blood lymphocytes stimulated in vitro with LPS. These findings provide new insight into the immunological consequences of the clinical use of beta2-agonists and may suggest new approaches for the treatment of Th1-mediated diseases.

Fractalkine (CX3CL1) as an amplification circuit of polarized Th1 responses

Fractalkine (FKN, CX3CL1) is a membrane-bound CX3C chemokine induced by primary proinflammatory signals in vascular endothelial cells (ECs). Here we examined the role of FKN in polarized Th1 or Th2 responses. Proinflammatory signals, including LPS, IL-1, TNF, and CD40 ligand, induced FKN, as did IFN-gamma, which had synergistic activity with TNF. IL-4 and IL-13 did not stimulate the expression of FKN and markedly reduced induction by TNF and IFN-gamma. TNF alone or combined with IFN-gamma also induced release of soluble FKN, which was inhibited by IL-4 and IL-13. In light of this differential regulation of FKN by the master cytokines that control polarized responses, we analyzed the interaction of FKN with natural killer (NK) cells and polarized T-cell populations. NK cells expressed high levels of the FKN receptor CX3CR1 and responded to FKN. CX3CR1 was preferentially expressed in Th1 compared with Th2 cells. Th1 but not Th2 cells responded to FKN. By immunohistochemistry, FKN was expressed on ECs in psoriasis, a Th1-dominated skin disorder, but not in Th2-driven atopic dermatitis. Similarly, ECs in Mycobacterium tuberculosis granulomatous lymphadenitis, but not those in reactive lymph node hyperplasia or in Castelmans disease, showed immunoreactive FKN. These results indicate that regulated expression of FKN in ECs participates in an amplification circuit of polarized type I responses.

Regulation of the IL-12/IL-12R axis: a critical step in T-helper cell differentiation and effector function

Summary: Interleukin (IL)‐12 is required for the development of T‐helper (Th)1 cells, which have been shown to be important for protective cell‐mediated immune responses against a variety of intracellular pathogens. Recent studies have clarified the sources and the regulation ofIL‐12 production leading to Th1 development against microbes. Expression of IL‐12R is necessary for maintaining IL‐12 responsiveness and controlling Thl lineage commitment. Advances in this area have included a broader understanding of the factors involved in the regulation of the IL‐12Rβ2 signaling component. Expression of this receptor subunit in humans is critically influenced by IL‐12 and type I interferons. IL‐12 signaling results in STAT4 activation and interferon (IFN)‐γ production. Recent evidence suggests that IL‐12 also modulates a number of genes involved in leukocyte trafficking. Thus, IL‐12 is not only an important proinflammatory cytokine, which induces production of IFN‐γ and subsequent activation of phago‐cytic cells but also plays a major role in regulating the migration and proper positioning of effector cells.

Inhibition by IL-12 and IFN-α of I-309 and macrophage-derived chemokine production upon TCR triggering of human Th1 cells

Th1 and Th2 cells, which produce distinct sets of cytokines, differentially express several chemokine receptors that may regulate their tissue‐specific localization. Although the expression pattern and regulation of chemokines are likely to play a critical role in many immunopathological processes, they remain largely unknown. Here, we investigated the requirements for Th1 and Th2 cells to produce the Th2 cell‐attracting chemokines thymus and activation‐regulated chemokine (TARC), macrophage‐derived chemokine (MDC) and I‐309. TCR triggering of Th1 and Th2 cells leads to production of MDC and I‐309 (CCR4 and CCR8 ligands, respectively), whereas TARC (CCR4 ligand) is selectively produced by Th2 cells. Secretion of these chemokines appears to be independent of endogenous production of IL‐4 and IFN‐γ. IL‐12 and IFN‐α, cytokines that promote the differentiation of human Th1 cells, selectively inhibit secretion and mRNA expression of MDC and I‐309 by Th1 cells. Suppression of I‐309 secretion results in a decreased chemotactic effect on L1.2 cells transfected with human CCR8, indicating that IL‐12 and IFN‐α may inhibit the recruitment of CCR8‐expressing cells such as Th2 cells. The inhibition of Th2 cell‐attracting chemokines MDC and I‐309 illustrates a novel mechanism by which IL‐12 and IFN‐α could promote and maintain an ongoing Th1 response.

Chemokines Fail to Up-Regulate β1 Integrin-Dependent Adhesion in Human Th2 T Lymphocytes

Th1 and Th2 cells are functionally distinct subsets of CD4+ T lymphocytes whose tissue-specific homing to sites of inflammation is regulated in part by the differential expression of P- and E-selectin ligands and selected chemokine receptors. Here we investigated the expression and function of β1 integrins in Th1 and Th2 cells polarized in vitro. Th1 lymphocytes adhere transiently to the extracellular matrix ligands laminin 1 and fibronectin in response to chemokines such as RANTES and stromal cell-derived factor-1, and this process is paralleled by the activation of the Rac1 GTPase and by a rapid burst of actin polymerization. Selective inhibitors of phosphoinositide-3 kinase prevent efficiently all of the above processes, whereas the protein kinase C inhibitor bisindolylmaleimide prevents chemokine-induced adhesion without affecting Rac1 activation and actin polymerization. Notably, chemokine-induced adhesion to β1 integrin ligands is markedly reduced in Th2 cells. Such a defect cannot be explained by a reduced sensitivity to chemokine stimulation in this T cell subset, nor by a defective activation of the signaling cascade involving phosphoinositide-3 kinase, Rac1, and actin turnover, as all these processes are activated at comparable levels by chemokines in the two subsets. We propose that reduced β1 integrin-mediated adhesion in Th2 cells may restrain their ability to invade and/or reside in sites of chronic inflammation, which are characterized by thickening of basement membranes and extensive fibrosis, requiring efficient interaction with organized extracellular matrices.