2023 Cardiac Society of Australia and New Zealand Expert Position Statement on Catheter and Surgical Ablation for Atrial Fibrillation.

Catheter ablation for atrial fibrillation (AF) has increased exponentially in many developed countries, including Australia and New Zealand. This Expert Position Statement on Catheter and Surgical Ablation for Atrial Fibrillation from the Cardiac Society of Australia and New Zealand (CSANZ) recognises healthcare factors, expertise and expenditure relevant to the Australian and New Zealand healthcare environments including considerations of potential implications for First Nations Peoples. The statement is cognisant of international advice but tailored to local conditions and populations, and is intended to be used by electrophysiologists, cardiologists and general physicians across all disciplines caring for patients with AF. They are also intended to provide guidance to healthcare facilities seeking to establish or maintain catheter ablation for AF.

Activin-A: a novel dendritic cell-derived cytokine that potently attenuates CD40 ligand-specific cytokine and chemokine production.

Activin-A is a transforming growth factor-beta (TGF-beta) superfamily member that plays a pivotal role in many developmental and reproductive processes. It is also involved in neuroprotection, apoptosis of tumor and some immune cells, wound healing, and cancer. Its role as an immune-regulating protein has not previously been described. Here we demonstrate for the first time that activin-A has potent autocrine effects on the capacity of human dendritic cells (DCs) to stimulate immune responses. Human monocyte-derived DCs (MoDCs) and the CD1c(+) and CD123(+) peripheral blood DC populations express both activin-A and the type I and II activin receptors. Furthermore, MoDCs and CD1c(+) myeloid DCs rapidly secrete high levels of activin-A after exposure to bacteria, specific toll-like receptor (TLR) ligands, or CD40 ligand (CD40L). Blocking autocrine activin-A signaling in DCs using its antagonist, follistatin, enhanced DC cytokine (IL-6, IL-10, IL-12p70, and tumor necrosis factor-alpha [TNF-alpha]) and chemokine (IL-8, IP-10, RANTES, and MCP-1) production during CD40L stimulation, but not TLR-4 ligation. Moreover, antagonizing DC-derived activin-A resulted in significantly enhanced expansion of viral antigen-specific effector CD8(+) T cells. These findings establish an immune-regulatory role for activin-A in DCs, highlighting the potential of antagonizing activin-A signaling in vivo to enhance vaccine immunogenicity.

P2Y receptor signaling regulates phenotype and IFN-alpha secretion of human plasmacytoid dendritic cells.

Plasmacytoid dendritic cells (PDCs) play powerful regulatory roles in innate and adaptive immune responses and are a major source of type I interferon (IFN) following viral infection. During inflammation and mechanical stress, cells release nucleotides into the extracellular space where they act as signaling molecules via G protein-coupled P2Y receptors. We have previously reported on the regulation of myeloid dendritic cell (DC) function by nucleotides. Here, we report that human PDCs express several subtypes of P2Y receptors and mobilize intracellular calcium in response to nucleotide exposure. As a functional consequence, PDCs acquire a mature phenotype that is further enhanced in the context of CD40 ligation. Strikingly, nucleotides strongly inhibit IFN-alpha secretion induced by influenza virus or CpG-A. This effect is most pronounced for the uridine nucleotides UDP and UTP and the sugar nucleotide UDP-glucose, ligands of P2Y(6), P2Y(4), and P2Y(14), respectively. Nucleotide-induced inhibition of IFN-alpha production is blocked by suramin, a P2Y receptor antagonist. Pharmacological data point toward a role of protein kinase C in the negative regulation of type I IFN. Manipulating PDC function with P2Y receptor agonists may offer novel therapeutic strategies for autoimmune diseases or cancer.

Gene structure and transcript analysis of the human and mouse EGF-TM7 molecule, FIRE.

The epidermal growth factor-transmembrane seven (EGF-TM7) family are proteins that express EGF-like domains at their extracellular N-terminus coupled to a classical seven transmembrane (TM7) cassette. Recently, we identified, in mice, a novel member of this family termed FIRE (EMR-4). Here, we present the structure of the mouse and human FIRE genes. The structures of the two genes are strikingly similar, with the positions of the introns, relative to the deduced protein sequences, highly conserved. Moreover, the gene structures are typical of other members of the EGF-TM7 family. Other researchers have identified a point deletion in exon eight of the human FIRE gene, which introduces a frame shift into the cDNA leading to a premature stop codon. Thus, human FIRE is predicted to be expressed only as a soluble protein; even though sequence potentially encoding the TM7 cassette is found in a separate open reading frame of the same mRNA transcript. We explored the possibility that a cell surface expressed form of human FIRE did exist, either as an allelic variant, or as an alternatively spliced transcript. Although, we did identify two alternatively spliced human FIRE transcripts, neither are predicted to express the TM7 cassette. Thus if human FIRE exists, it is likely to be expressed as a soluble secreted molecule.

Extracellular nucleotide signaling by P2 receptors inhibits IL-12 and enhances IL-23 expression in human dendritic cells: a novel role for the cAMP pathway.

The interleukin-12 (IL-12) cytokine family plays important roles in the orchestration of innate and adaptive immunity by dendritic cells (DCs). The regulation of IL-12 expression has been thoroughly studied, but little is known about factors governing the expression of IL-23 and IL-27, 2 novel IL-12 family members acting on memory and naive T cells, respectively. We report that the expression of these cytokines by DCs was critically dependent on the mode of activation. DC activation by CD40L predominantly induced IL-12. Ligands of the Toll-like receptor (TLR) 3 and TLR4 induced IL-12 and IL-27, whereas exposure to intact Escherichia coli resulted in high expression of IL-12, IL-27, and IL-23. The nucleotide adenosine triphosphate (ATP) has been shown to inhibit IL-12 production by P2 receptors. We found that ATP also inhibited IL-27 expression but enhanced IL-23 expression. Interestingly, the reciprocal regulation of IL-12/IL-27 and IL-23 by ATP was mediated by 2 distinct P2 receptors and was also induced by prostaglandin E(2) by cyclic adenosine monophosphate (cAMP)-elevating EP2/EP4 receptors. As a consequence, DCs were selectively impaired in their ability to induce interferon-gamma (IFN-gamma) in naive T cells but continued to promote IFN-gamma and IL-17 production in memory T cells. These studies identify P2 receptors as promising targets for the design of novel strategies to manipulate specific stages of T-cell responses and to treat IL-12- and IL-23-mediated disorders.

Tumor antigen processing and presentation depend critically on dendritic cell type and the mode of antigen delivery.

Dendritic cells (DCs) are being evaluated for cancer immunotherapy due to their unique ability to induce tumor-directed T-cell responses. Here we report that the type of human DC, the mode of activation, and the strategy for delivery of antigen are 3 critical factors for efficient stimulation of tumor-specific CD8+ and CD4+ T cells. Only CD1c+ blood DCs and monocyte-derived DCs (MoDCs) were capable of presenting epitopes of the full-length tumor antigen NY-ESO-1 on both major histocompatibility complex (MHC) class I (cross-presentation) and MHC II, whereas plasmacytoid DCs were limited to MHC II presentation. Cross-presentation was inefficient for soluble protein, but highly efficient for antigen-antibody immune complexes (NY-ESO-1/IC) and for protein formulated with ISCOMATRIX adjuvant (NY-ESO-1/IMX). DC activation with CD40L further enhanced cross-presentation efficiency. The mode of antigen delivery was found to be a determining factor for cytosolic proteolysis by DCs. Immune complexes (ICs) targeted a slow, proteasome-dependent cross-presentation pathway, whereas ISCOMATRIX (IMX) targeted a fast, proteasome-independent pathway. Both cross-presentation pathways resulted in a long-lived, T-cell stimulatory capacity, which was maintained for several days longer than for DCs pulsed with peptide. This may provide DCs with ample opportunities for sensitizing tumor-specific T cells against a broad array of tumor antigen epitopes in lymph nodes.

Role of adenosine receptors in regulating chemotaxis and cytokine production of plasmacytoid dendritic cells.

Plasmacytoid dendritic cells (PDCs) are potent regulators of immune function and the major source of type I interferon (IFN) following viral infection. PDCs are found at sites of inflammation in allergic reactions, autoimmune disorders, and cancer, but the mechanisms leading to the recruitment of PDCs to these sites remain elusive. During inflammation, adenosine is released and functions as a signaling molecule via adenosine receptors. This study analyzes adenosine receptor expression and function in human PDCs. Adenosine was found to be a potent chemotactic stimulus for immature PDCs via an A(1) receptor-mediated mechanism. The migratory response toward adenosine was comparable to that seen with CXCL12 (stromal-derived factor-1 alpha [SDF-1 alpha), the most potent chemotactic stimulus identified thus far for immature PDCs. Upon maturation, PDCs down-regulate the A(1) receptor, resulting in a loss of migratory function. In contrast, mature PDCs up-regulate the A(2a) receptor, which is positively coupled to adenylyl cyclase and has been implicated in the down-regulation of DC cytokine-producing capacity. We show that in mature PDCs adenosine reduces interleukin-6 (IL-6), IL-12, and IFN-alpha production in response to CpG oligodeoxynucleotides (ODN). These findings indicate that adenosine may play a dual role in PDC-mediated immunity by initially recruiting immature PDCs to sites of inflammation and by subsequently limiting the extent of the inflammatory response induced by mature PDCs by inhibiting their cytokine-producing capacity.

Functional comparison of DCs generated in vivo with Flt3 ligand or in vitro from blood monocytes: differential regulation of function by specific classes of physiologic stimuli.

Dendritic cells (DCs) are a family of leukocytes that initiate T- and B-cell immunity against pathogens. Migration of antigen-loaded DCs from sites of infection into draining lymphoid tissues is fundamental to the priming of T-cell immune responses. In humans, the major peripheral blood DC (PBDC) types, CD1c+ DCs and interleukin 3 receptor-positive (IL-3R+) plasmacytoid DCs, are significantly expanded in vivo with the use of Flt3 ligand (FL). DC-like cells can also be generated from monocyte precursors (MoDCs). A detailed comparison of the functional potential of these types of DCs (in an autologous setting) has yet to be reported. Here, we compared the functional capacity of FL-expanded CD1c+ PBDCs with autologous MoDCs in response to 3 different classes of stimuli: (1) proinflammatory mediators, (2) soluble CD40 ligand trimer (CD40L), and (3) intact bacteria (Escherichia coli). Significant differences in functional capacities were found with respect to changes in phenotype, migratory capacity, cytokine secretion, and T-cell stimulation. MoDCs required specific stimuli for the expression of functions. They responded vigorously to CD40L or E coli, expressing cytokines known to regulate interferon-gamma (IFN-gamma) in T cells (IL-12p70, IL-18, and IL-23), but required prostaglandin E2 (PGE2) during stimulation to migrate to chemokines. In contrast, PBDCs matured in response to minimal stimulation, rapidly acquired migratory function in the absence of PGE2-containing stimuli, and were low cytokine producers. Interestingly, both types of DCs were equivalent with respect to stimulation of allogeneic T-cell proliferation and presentation of peptides to cytotoxic T lymphocyte (CTL) lines. These distinct differences are of particular importance when considering the choice of DC types for clinical applications.

ATP gradients inhibit the migratory capacity of specific human dendritic cell types: implications for P2Y11 receptor signaling.

Dendritic cells (DCs) are specialized antigen-presenting cells residing in tissues, from which they take up antigen. Activated DCs migrate through chemokine gradients from sites of inflammation to lymph nodes to stimulate T cells. At sites of inflammation, nucleotides, such as adenosine triphosphate (ATP), are released by activated or dying cells and can function as signaling molecules through P2 receptors (P2Rs). We investigated P2R expression in different DC populations and the effect of nucleotides on chemokine-directed migration. Exposure of monocyte-derived DCs (MoDCs) and CD1a+ dermal DCs to gradients of ATP inhibited their migratory capacity in a dose-dependent manner. Studies using P2R agonists and antagonists implicated signaling through the P2Y11R. On maturation, MoDCs down-regulated P2Y11R expression and were less sensitive to ATP-mediated inhibition of migration. In contrast, ATP did not inhibit the migration of CD1c+ peripheral blood (PB) DCs or interleukin-3 receptor-positive (IL-3R+) plasmacytoid DCs. Although all 4 DC populations expressed mRNA for P2Y11R, calcium-flux studies showed that blood DC types were unresponsive to P2Y11R agonists. In conclusion, DCs use distinct subtypes of P2R. The formation of ATP gradients at sites of inflammation may transiently inhibit the migration of local DCs, thus prolonging the time of antigen encounter. P2R inhibition may represent a new strategy to improve the migration of antigen-loaded DCs from the vaccination site to lymph nodes.

Functionally distinct dendritic cell (DC) populations induced by physiologic stimuli: prostaglandin E(2) regulates the migratory capacity of specific DC subsets.

Migration of antigen (Ag)-loaded dendritic cells (DCs) from sites of infection into draining lymphoid tissues is fundamental to the priming of T-cell immune responses. We evaluated monocyte-derived DCs (MoDCs) and peripheral blood DCs (PBDCs) to respond to proinflammatory mediators, CD40L, and intact bacteria. All classes of stimuli induced DC phenotypic maturation. However, for MoDCs, only prostaglandin E(2) (PGE(2))-containing stimuli induced migratory-type DCs. Thus, immature MoDCs that encountered proinflammatory cytokines or CD40L or intact bacteria in the presence of PGE(2) acquired migratory capacity but secreted low levels of cytokines. Conversely, MoDCs that encountered pathogens or CD40L alone become nonmigratory cytokine-secreting cells (proinflammatory type). Interestingly, both migratory- and proinflammatory-type DCs expressed equivalent levels of chemokine receptors, suggesting that the role of PGE(2) was to switch on migratory function. We demonstrate that PGE(2) induces migration via the E-prostanoid 2/E-prostanoid 4 (EP(2)/EP(4)) receptors and the cAMP pathway. Finally, migratory-type MoDCs stimulated T-cell proliferation and predominantly IL-2 secretion, whereas proinflammatory-type MoDCs induced IFN-gamma production. In contrast, CD1b/c(+) PBDC rapidly acquired migratory capacity irrespective of the class of stimulus encountered and secreted low levels of cytokines. This suggests that not all mature stages of DCs are destined to migrate to lymphoid organs and that the sequence in which stimuli are encountered significantly affects which functions are expressed. Thus, certain immature DC subsets recruited from the resting precursor pool may have multiple functional fates that play distinct roles during the induction and effector phases of the immune response. These findings have important implications for the clinical utility of DCs in immunotherapy.

IFN-alpha enhances CD40 ligand-mediated activation of immature monocyte-derived dendritic cells.

Type I IFN are immune modulatory cytokines that are secreted during early stages of infection. Type I IFN bridge the innate and the adaptive immune system in humans and mice. We compared the capacity of type I and II IFN to induce the functional maturation of monocyte-derived dendritic cells (MoDC). Extending our earlier observation that type I IFN promote DC maturation, we report that these cytokines also enhance DC differentiation by augmenting CD40 ligand (CD40L)-induced cytokine secretion by MoDC. Type I IFN alone were poor inducers of MoDC maturation as compared with other stimuli. They up-regulated the expression of HLA-DR, CD80, CD86, partially CCR7 but not CD83, partially reduced antigen-uptake function, increased the levels of IL-12p35 mRNA, and prolonged surface expression of peptide-MHC class I complexes for presentation to cytotoxic T lymphocytes, but did not induce migration towards CCL21 chemokine. However, type I IFN were potent co-factors for CD40L-mediated function. Here, they enhanced CD40L-mediated IL-6, IL-10 and IL-12p70 secretion. Furthermore, when combined with IL-1beta and/or IL-4, IFN-alpha2a type I IFN increased CD40L-mediated IL-12p70 production by 2- to 3-fold, and biased the IL-12 p40/p70 ratio towards the IFN-gamma inducing p70 heterodimer, this correlating with higher levels of IFN-gamma secretion by allogeneic T cell subsets and NK cells. Our results suggest that the rapid expression of CD40L, IFN and IL-1beta at sites of infection and inflammation can act in concert on immature DC, thereby linking innate and adaptive immune responses. In this way, type I IFN play a dual role as DC maturation factors and enhancers of CD40L-mediated DC activation.