The role of interleukin 2 (IL-2) and serum-soluble IL-2 receptor cells in idiopathic IgA nephropathy.

Interleukin 2 (IL-2) plays a central role in the immune response and may be involved in the derangement of cellular immunoregulation of idiopathic IgA nephropathy (IgAN). The aim of this study was to investigate the serum levels and production of IL-2 from peripheral blood mononuclear cells (PBMC) and the distribution of IL-2 receptor cells and serum-soluble IL-2 receptor cells (sIL-2R) in patients with IgAN. Twenty-four patients with IgA nephropathy and 11 healthy controls (age and sex matched) were studied during an infection-free period without signs of clinical activity at the moment of the study. Serum IL-2 concentrations did not differ between patients and controls. The supernatant levels of IL-2 taken from 24-hr cultures of PBMC stimulated with phytohemagglutinin or tumor necrosis factor increased significantly in the patients but not in the controls. The percentage of IL-2R positive cells (CD25+) was increased in patients compared with controls. Moreover, IgAN patients had increased activated CD4+ lymphocytes when compared with the controls. Serum levels of sIL-2R were significantly higher in patients than in controls. There were no correlations among renal function, serum IgA levels, and urinary findings with cellular subsets or with IL-2 levels. However, sIL-2R was higher in the subgroup of patients with episodic macrohematuria and was closely related with the presence of red blood cells in the urinary sediment. We conclude that PBMC of IgA nephropathy patients have an overproduction of IL-2 after mitogenic stimulation, an increased helper T cell activity, increased IL-2R+ cells, and elevated serum levels of sIL-2R. These alterations are present in periods of apparent clinical inactivity. Finally, sIL-2R is closely related with hematuria, providing a good marker for disease activity. Our results suggest a pivotal role of IL-2 in cellular immune responses with regard to T cell activation in patients with IgAN.