adenosine-5--(n-ethylcarboxamide) and Autoimmune-Diseases

Adenosine is a key endogenous signaling molecule that regulates a wide range of physiological functions, including immune system function and inflammation. Studies have shown that adenosine receptor (AR) agonists can be either anti-inflammatory or proinflammatory in immune responses and in inflammation, and the clarification of the mechanisms causing these opposing effects should provide a better guide for therapeutic intervention. Whereas previous studies mostly examined the effects of AR agonists on Th1-type immune responses, in this study, we compared their effect on Th17 and Th1 autoimmune responses in experimental autoimmune uveitis, a mouse model of human uveitis induced by immunization with the human interphotoreceptor retinoid-binding protein peptides 1-20. We showed that injection of mice with a nonselective AR agonist, 5'-N-ethylcarboxamidoadenosine (NECA), at an early stage after immunization had an inhibitory effect on both Th1 and Th17 responses, whereas injection of the same amount of NECA at a late stage inhibited the Th1 response but had an enhancing effect on the Th17 response. We also showed that the effects of NECA on Th1 and Th17 responses were completely dissociated, that the enhancing effect of NECA on Th17 responses was modulated by γδ T cells, and that the response of γδ T cells to NECA was determined by their activation status. We conclude that the inflammatory environment has a strong impact on converting the effect of AR agonist on the Th17 autoimmune response from anti-inflammatory to proinflammatory. Our observation should help in the designing of better AR-targeted therapies.

Topics: Adenosine-5'-(N-ethylcarboxamide); Animals; Anti-Inflammatory Agents; Autoantigens; Autoimmune Diseases; Cells, Cultured; Eye Proteins; Female; Humans; Immunomodulation; Inflammation Mediators; Lymphocyte Activation; Mice; Mice, Inbred C57BL; Mice, Knockout; Models, Animal; Peptide Fragments; Purinergic P1 Receptor Agonists; Receptors, Antigen, T-Cell, gamma-delta; Retinol-Binding Proteins; Th1 Cells; Th17 Cells; Uveitis

We conducted the present study to investigate protein expression and functioning of A2A and A2B adenosine receptors (ARs) in neutrophils of patients affected by systemic sclerosis (SSc). The presence of A2A and A2B ARs was assessed by immunoblotting using specific antibodies. Equilibrium A2A and A2B ARs binding parameters were evaluated by radioligand binding assay. Functional studies were conducted to investigate coupling of the A2B AR to the adenylyl cyclase pathway. This is the first report of the use of Western blot analysis to confirm the presence of A2A and A2B ARs in human neutrophils. No significant changes in A2A AR binding parameters or expression levels were detected between SSc patients and healthy control individuals. A significant decrease (65%) in the maximum density of A2B AR binding sites occurred in SSc neutrophils, whereas no changes in the affinity constant values were found. Moreover, a decrease in A2B AR mediated adenylyl cyclase activity was observed in patients with SSc. Our findings demonstrate the occurrence of selective alterations in A2B AR density and signalling in SSc.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Adenylyl Cyclases; Adult; Aged; Autoimmune Diseases; Blotting, Western; Cyclic AMP; Female; Humans; Male; Middle Aged; Neutrophils; Phenethylamines; Radioligand Assay; Receptor, Adenosine A2A; Receptor, Adenosine A2B; Receptors, G-Protein-Coupled; Scleroderma, Systemic; Signal Transduction

Anti-neutrophil cytoplasm antibodies (ANCA) with specificity for myeloperoxidase (MPO) are implicated as pathogenic agents in pauci-immune systemic vasculitis. In agreement with previously published observations we show that human neutrophils incubated with an MPO-specific IgG class monoclonal antibody are pro-adhesive and undergo apoptosis more readily in vitro. If apoptotic neutrophils are incubated with this antibody they are readily phagocytosed by macrophages and we show that 'blocking' antibodies to FcgammaRIIa (CD32) on the macrophage inhibit this process. We also examined the effect of E3MPO, a monoclonal anti-MPO antibody derived from a patient with severe systemic vasculitis. E3MPO is closely related to the cold-agglutinins and bears an epitope recognized by the monoclonal antibody 9G4 which is expressed on antibodies derived from the V4-34 germ-line immunoglobulin gene. In previous studies, we have shown that anti-MPO antibodies present in sera from patients with vasculitis often bear this epitope. In contrast to the IgG-class antibody, incubation of neutrophils with E3MPO inhibited neutrophil adhesion and apoptosis. Apoptotic neutrophils however were phagocytosed more readily by macrophages in the presence of E3MPO. The effects of E3MPO on neutrophil adhesion and apoptosis were inhibited by piceatannol, an inhibitor of Syk-family kinases; activation of which is associated with cross-linking of the beta(2)-integrins. We show that surface-expressed MPO co-localizes with these beta(2)-integrins and suggest that cross-linking of beta(2)-integrin-bound MPO by polyvalent antibodies could result in signaling through these receptors. We have demonstrated that there are different consequences of Fcgamma-receptor-dependent and -independent signaling mediated by ANCA.

Topics: Adenosine; Adenosine A1 Receptor Agonists; Adenosine-5'-(N-ethylcarboxamide); Animals; Antibodies, Antineutrophil Cytoplasmic; Antibodies, Monoclonal; Apoptosis; Autoantigens; Autoimmune Diseases; CD18 Antigens; Cell Adhesion; Enzyme Inhibitors; Enzyme Precursors; Humans; Hyaluronan Receptors; Immunoglobulin G; Immunoglobulin M; Intracellular Signaling Peptides and Proteins; Macrophages; Mice; Neutrophils; Opsonin Proteins; Peroxidase; Phagocytosis; Phenethylamines; Protein-Tyrosine Kinases; Receptors, IgG; Signal Transduction; Stilbenes; Syk Kinase; Vasculitis