Naturally occurring regulatory T cells (T reg cells) are a thymus-derived subset of T cells, which are crucial for the maintenance of peripheral tolerance by controlling potentially autoreactive T cells. However, the underlying molecular mechanisms of this strictly cell contact–dependent process are still elusive. Here we show that naturally occurring T reg cells harbor high levels of cyclic adenosine monophosphate (cAMP). This second messenger is known to be a potent inhibitor of proliferation and interleukin 2 synthesis in T cells. Upon coactivation with naturally occurring T reg cells the cAMP content of responder T cells is also strongly increased. Furthermore, we demonstrate that naturally occurring T reg cells and conventional T cells communicate via cell contact–dependent gap junction formation. The suppressive activity of naturally occurring T reg cells is abolished by a cAMP antagonist as well as by a gap junction inhibitor, which blocks the cell contact–dependent transfer of cAMP to responder T cells. Accordingly, our results suggest that cAMP is crucial for naturally occurring T reg cell–mediated suppression and traverses membranes via gap junctions. Hence, naturally occurring T reg cells unexpectedly may control the immune regulatory network by a well-known mechanism based on the intercellular transport of cAMP via gap junctions.

Background—: Angiotensin II (ATII), a potent vasoconstrictor, causes hypertension, promotes infiltration of myelomonocytic cells into the vessel wall, and stimulates both vascular and inflammatory cell NADPH oxidases. The predominant source of reactive oxygen species, eg, vascular (endothelial, smooth muscle, adventitial) versus phagocytic NADPH oxidase, and the role of myelomonocytic cells in mediating arterial hypertension have not been defined yet. Methods and Results—: Angiotensin II (1 mg · kg ⁻¹ · d ⁻¹ for 7 days) increased the number of both CD11b ⁺ Gr-1 ^low F4/80 ⁺ macrophages and CD11b ⁺ Gr-1 ^high F4/80 ⁻ neutrophils in mouse aorta (verified by flow cytometry). Selective ablation of lysozyme M-positive (LysM ⁺ ) myelomonocytic cells by low-dose diphtheria toxin in mice with inducible expression of the diphtheria toxin receptor (LysM ^iDTR mice) reduced the number of monocytes in the circulation and limited ATII-induced infiltration of these cells into the vascular wall, whereas the number of neutrophils was not reduced. Depletion of LysM ⁺ cells attenuated ATII-induced blood pressure increase (measured by radiotelemetry) and vascular endothelial and smooth muscle dysfunction (assessed by aortic ring relaxation studies) and reduced vascular superoxide formation (measured by chemiluminescence, cytochrome c assay, and oxidative fluorescence microtopography) and the expression of NADPH oxidase subunits gp91 ^phox and p67 ^phox (assessed by Western blot and mRNA reverse-transcription polymerase chain reaction). Adoptive transfer of wild-type CD11b ⁺ Gr-1 ⁺ monocytes into depleted LysM ^iDTR mice reestablished ATII-induced vascular dysfunction, oxidative stress, and arterial hypertension, whereas transfer of CD11b ⁺ Gr-1 ⁺ neutrophils or monocytes from gp91 ^phox or ATII receptor type 1 knockout mice did not. Conclusions—: Infiltrating monocytes with a proinflammatory phenotype and macrophages rather than neutrophils appear to be essential for ATII-induced vascular dysfunction and arterial hypertension.

Nucleotide signaling molecules contribute to the regulation of cellular pathways. In the immune system cAMP is well established as a potent regulator of innate and adaptive immune cell functions. Therapeutic strategies to interrupt or enhance cAMP generation or effects have immunoregulatory potential in autoimmune and inflammatory disorders. Here, we provide an overview of the cyclic AMP axis and its role as a regulator of immune functions and discuss the clinical and translational relevance of interventions with these processes.

CD4+CD25+Foxp3+ regulatory T cells (CD25+ Treg cells) direct the maintenance of immunological self-tolerance by active suppression of autoaggressive T-cell populations. However, the molecules mediating the anergic state and regulatory function of CD25+ Treg cells are still elusive. Using differential proteomics, we identified galectin-10, a member of the lectin family, as constitutively expressed in human CD25+ Treg cells, while they are nearly absent in resting and activated CD4+ T cells. These data were confirmed on the mRNA and protein levels. Single-cell staining and flow cytometry showed a strictly intracellular expression of galectin-10 in CD25+ Treg cells. Specific inhibition of galectin-10 restored the proliferative capacity of CD25+ Treg cells and abrogated their suppressive function. Notably, first identified here as expressed in human T lymphocytes, galectin-10 is essential for the functional properties of CD25+ Treg cells.

Objective—: Immune cells contribute to angiotensin II (ATII)–induced vascular dysfunction and inflammation. Interferon-γ (IFN-γ), an inflammatory cytokine exclusively produced by immune cells, seems to be involved in ATII-driven cardiovascular injury, but the actions and cellular source of IFN-γ remain incompletely understood. Approach and Results—: IFN-γ ^−/− and Tbx21 ^−/− mice were partially protected from ATII-induced (1 mg/kg per day of ATII, infused subcutaneously by miniosmotic pumps) vascular endothelial and smooth muscle dysfunction, whereas mice overexpressing IFN-γ showed constitutive vascular dysfunction. Absence of T-box expressed in T cells (T-bet), the IFN-γ transcription factor encoded by Tbx21, reduced vascular superoxide and peroxynitrite formation and attenuated expression of nicotinamide adenosine dinucleotide phosphate oxidase subunits as well as inducible NO synthase, monocyte chemoattractant protein 1, and interleukin-12 in aortas of ATII-infused mice. Compared with controls, IFN-γ ^−/− and Tbx21 ^−/− mice were characterized by reduced ATII-mediated vascular recruitment of both natural killer (NK)1.1 ⁺ NK-cells as the major producers of IFN-γ and CD11b ⁺ Gr-1 ^low interleukin-12 secreting monocytes. Selective depletion and adoptive transfer experiments identified NK-cells as essential contributors to vascular dysfunction and showed that T-bet ⁺ lysozyme M ⁺ myelomonocytic cells were required for NK-cell recruitment into vascular tissue and local IFN-γ production. Conclusions—: We provide first evidence that NK-cells play an essential role in ATII-induced vascular dysfunction. In addition, we disclose the T-bet-IFN-γ pathway and mutual monocyte–NK-cell activation as potential therapeutic targets in cardiovascular disease.