Regulation of innate immunity by the nucleotide pathway in children with idiopathic nephrotic syndrome

Abstract

Summary Activation of the oxidative burst and failure of CD4+CD25+ cell regulation have been implicated in idiopathic nephrotic syndrome (iNS). The intimate mechanism is, however, unknown and requires specifically focused studies. We investigated reactive oxygen species (ROS) generation [di-chlorofluorescein-diacetate (DCFDA)] fluorescence assay and the regulatory adenosine 5′-triphosphate (ATP) pathways in the blood of 41 children with iNS, utilizing several agonists and antagonists of nucleotide/nucleoside receptors, including the addition of soluble apyrase. The CD4+CD25+CD39+/CD73+ expression was determined in vivo in parallel during disease activity. Overall, we found that the percentage of CD39+CD4+CD25+ was reduced markedly in iNS by 80% (3·43 ± 0·04% versus 13·14 ± 0·07% of total lymphocytes, P < 0·001). In these patients, reactive oxygen species (ROS) generation by polymorphonuclear neutrophils (PMN) at rest was a function of apyrase (CD39) expressed by CD4+CD25+, with higher rates in patients with very low CD39+CD4+CD25+ levels (< 7·5%). Addition of apyrase reduced ROS generation by 40% in both iNS and controls and was mainly effective in patients. The quota of ROS surviving ATP elimination was higher still in iNS. In vitro studies to limit ROS generation with adenosine analogues (2′-chloroadenosine and 5′-N-ethylcarboxamidoadenosine) produced minor effects. At variance, antagonizing ATP efflux with carbenoxolone or by antagonizing ATP effects (Brilliant Blue G, KN62 and A437089) reduced ROS generation comparable to apyrase. These results confirm a key role of ATP in the regulation of innate immunity and minimize the effect of adenosine. Decreased CD39+CD4+CD25+ expression in iNS highlights an impairment of ATP degradation in this pathology. However, high ROS surviving ATP consumption implies a major role of other regulatory pathways.