IgG4- related disease as a rare cause of tubulointerstitial nephritis.

Isolated IgG4 tubulointerstitial nephritis (TIN) is a rare disorder characterized by raised serum IgG4 levels and histological findings of dense lymphoplasmacytic infiltrates rich in IgG4 positive plasma cells. We report a case of isolated IgG4 TIN that presented with acute kidney injury in an 84 year old man with a polyclonal increase in his total IgG and a raised IgE of 381 kUA/L but without evidence of systemic autoimmunity. We draw a parallel with IgG4-related autoimmune pancreatitis and show raised levels of circulating regulatory T cells. Importantly the plasma levels of the T regulatory cell cytokine, IL10, the TH1 cytokines IL12 and IFNγ, the proinflammatory TNF α and immune regulatory IL27 were all highly raised. Furthermore, the level of IL21 that promotes IgG4 production was also very significantly elevated. These results suggest efforts of the immune system to reduce inflammation and suppress an exaggerated Th2 response. A raised serum IgG in the setting of acute kidney injury and in the absence of autoimmunity and chronic infection should encourage an assessment of the IgG subclasses. Prompt steroid treatment of those with a raised IgG4 may reduce ongoing renal damage.