Toll‐like receptor 4 expression is increased in circulating mononuclear cells of patients with immunoglobulin A nephropathy

Summary We investigated Toll‐like receptors (TLR‐3, ‐4 and ‐7) expression in circulating mononuclear cells of patients with immunoglobulin A nephropathy (IgAN), a disease with debated relationships with mucosal immunity. TLR‐4 expression (detected by fluorescence activated cell sorter) and mRNA transcriptional levels ( Taq man) were significantly higher in patients with IgAN than in healthy controls ( P  = 0·00200 and P  = 0·0200). TLR‐3 and TLR‐7 were not modified significantly. In IgAN patients proteinuria was correlated significantly with TLR‐4 expression ( P  = 0·0312). In a group of nephrotic syndromes, TLR‐3, ‐4 and ‐7 expression was similar to healthy controls. A significant difference in TLR‐4 expression and mRNA levels was found between very active IgAN patients (proteinuria > 1 g/1·73 m 2 /day in association with severe microscopic haematuria) and inactive patients (proteinuria < 0·5 g/1·73 m 2 /day, with absent or minimal haematuria). No correlation with levels of aberrantly glycosylated IgA1, age, renal biopsy features or therapy was found. This study shows for the first time an up‐regulation of TLR‐4 in circulating mononuclear cells of patients with IgAN, particularly in association with proteinuria and heavy microscopic haematuria.