RESUMEN
Sjögren's syndrome (SS) is a chronic autoimmune disease characterized by salivary and lacrimal gland dysfunction. Clinical observations and results from animal models of SS support the role of aberrant epithelial cell apoptosis and immune homeostasis loss in the glands as triggering factors for the autoimmune response. Vasoactive intestinal peptide (VIP) promotes potent anti-inflammatory effects in several inflammatory and autoimmune disease models, including the non-obese diabetic (NOD) mouse model of SS. With the knowledge that VIP modulates monocyte function through vasoactive intestinal peptide receptors (VPAC) and that immune homeostasis maintenance depends strongly upon a rapid and immunosuppressant apoptotic cell clearance by monocytes/macrophages, in this study we explored VPAC expression on monocytes from primary SS (pSS) patients and the ability of VIP to modulate apoptotic cell phagocytic function and cytokine profile. Monocytes isolated from individual pSS patients showed an increased expression of VPAC2 subtype of VIP receptors, absent in monocytes from control subjects, with no changes in VPAC1 expression. VPAC2 receptor expression could be induced further with lipopolysaccharide (LPS) in pSS monocytes and VIP inhibited the effect. Moreover, monocytes from pSS patients showed an impaired phagocytosis of apoptotic epithelial cells, as evidenced by reduced engulfment ability and the failure to promote an immunosuppressant cytokine profile. However, VIP neither modulated monocyte/macrophage phagocytic function nor did it reverse their inflammatory profile. We conclude that monocytes from pSS patients express high levels of VPAC2 and display a deficient clearance of apoptotic cells that is not modulated by VIP.
Asunto(s)
Apoptosis , Citofagocitosis/genética , Citofagocitosis/inmunología , Monocitos/inmunología , Monocitos/metabolismo , Receptores de Tipo II del Péptido Intestinal Vasoactivo/genética , Síndrome de Sjögren/genética , Síndrome de Sjögren/inmunología , Adulto , Anciano , Estudios de Casos y Controles , Citofagocitosis/efectos de los fármacos , Regulación de la Expresión Génica/efectos de los fármacos , Humanos , Lipopolisacáridos/inmunología , Persona de Mediana Edad , Monocitos/efectos de los fármacos , Receptores de Péptido Intestinal Vasoactivo , Péptido Intestinal Vasoactivo/farmacología , Adulto JovenRESUMEN
Phagocytosis plays an important role in controlling inflammation and antigen cross-presentation through the uptake of apoptotic bodies from dying cells. As dying cells are known to release nucleotides and other "danger signals", we investigated whether extracellular nucleotides may affect phagocytosis through binding to P2 purinergic receptors on phagocytic cells. We here show that the purinergic receptor agonists, ATP, ADP, α,ß-methylene ATP (α,ß-meATP), 3'-O-(4-benzoyl)benzoyl ATP, UTP and UDP, increased phagocytosis of latex beads, and some of them increased endocytosis and/or macropinocytosis of dextran by macrophages. The enhanced phagocytosis could be inhibited by pre-treatment with the P2X and P2Y antagonists, pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid and suramin, and the P2Y1-selective antagonist, MRS2179. The nucleotides induced upregulation in macrophages of the ß2 integrin CD11b/CD18 (Mac-1) and the vitronectin receptor (α(v)ß3, CD51/CD61), both of which are involved in recognition and internalization of apoptotic cells. In addition, ATP and α,ß-meATP increased adhesion of apoptotic cells to macrophages, both in vitro and in vivo, and α,ß-meATP had a small effect on adhesion of necrotic cells. The nucleotides had no effect on adhesion of viable cells. We propose that engagement of the P2 receptors (P2X1, or P2X3) by extracellular nucleotides released from dying cells increases the ability of macrophages to bind apoptotic bodies, thus enhancing their ability to internalize and present antigens from the dying cells.